Patent Publication Number: US-2021169924-A1

Title: Prevention and treatment of ocular infection, composition and methods thereof

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 62/943,414 filed Dec. 4, 2019, which is incorporated by reference in its entirety. 
    
    
     1. FIELD 
     The present disclosure relates to a pharmaceutical composition and method of prevention and treatment of ocular infection. 
     SEQUENCE LISTING 
     The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Jan. 8, 2021, is named 10030_008239-US1 and is 5.22 KB in size. 
     2. BACKGROUND 
     Keratitis, inflammation of the cornea, is caused by both infectious and non-infectious agents. Infective keratitis, an ophthalmologic emergency that requires prompt diagnosis and expedient treatment so as to prevent visual loss, can be caused by bacteria, viruses, fungi, or parasites. Among the infectious agents, bacterial pathogens are responsible for the majority of microbial keratitis. Bacterial keratitis is often associated with wearing contact lenses or other microtrauma, such as trichiasis, to the epithelial surface of the cornea. Among the cases of bacterial keratitis of which an etiology can be identified, most are caused by  Staphylococcus aureus  and  Streptococcus pneumoniae.    
       Tsukamurella  are Gram-positive, aerobic and partially acid-fast bacteria. Traditionally, the most commonly reported  Tsukamurella  infections in human are indwelling device-related infections, such as catheter-related bacteremia and peritonitis associated with continuous ambulatory peritoneal dialysis 1-4 . 
     The optimal treatment and pathogenesis of  Tsukamurella  keratitis is largely unknown. Common contact lens disinfecting solutions were ineffective against  Tsukamurella . There is a need to develop a disinfection and treatment strategy against  Tsukamurella.    
     3. SUMMARY 
     Provided herein are compositions for the treating or preventing an ocular infection, for example, bacterial conjunctivitis caused by an antibiotic-resistant bacterium. A further feature of the present disclosure is to provide a composition that can provide an easy and non-toxic way to treat an ocular infection and/or the source of the ocular infection. In one embodiment, the infection is bacterial conjunctivitis. In one embodiment, the infection is bacterial keratitis. Provided herein is a method to reduce virulence of  Tsukamurella  comprising a step of decreasing the expression of tmytC gene wherein the reduction of the virulence is characterized by at least one of: (i) reduced biofilm formation; (ii) reduced adherence property; (iii) reduced polymorphonuclear leukocyte (“PMN”) infiltration; (iv) reduced epithelial damage; and (v) reduced corneal bacterial loads. 
     In one embodiment, the expression of tmytC gene is decreased by knock-out of the tmytC gene. 
     In one embodiment, the expression of tmytC gene is decreased by introducing a homologous recombination construct comprising: (i) a vector comprising a promoter expressing a marker; (ii) a 5′ flanking region of the tmytC gene; (iii) and a 3′ flanking region of the tmytC gene. 
     Provided herein is a homologous recombination construct comprising: (i) a vector comprising a promoter expressing a marker; (ii) a 5′ flanking region of the tmytC gene; (iii) and a 3′ flanking region of the tmytC gene. 
     Provided herein is a host cell comprising the homologous recombination construct comprising: (i) a vector comprising a promoter expressing a marker; (ii) a 5′ flanking region of the tmytC gene; (iii) and a 3′ flanking region of the tmytC gene. 
     Provided herein is a modified  Tsukamurella  that has a reduced expression of tmytC. In one embodiment, the modified  Tsukamurella  does not express tmytC. 
     Provided herein is a method of treating an ocular bacterial infection in a subject, said method comprises a step of administering to the subject a homologous recombination construct comprising: (i) a vector comprising a promoter expressing a marker; (ii) a 5′ flanking region of the tmytC gene; and (iii) a 3′ flanking region of the tmytC gene. 
     Provided herein is a method of treating or preventing ocular bacterial infection in a subject comprising a step of administering to the subject a composition comprising one or more  Tsukamurella  tmytC inhibitors. 
     In one embodiment, the ocular bacterial infection is treated or prevented as characterized by at least one of: (i) reduced biofilm formation; (ii) reduced adherence property of the bacteria; (iii) reduced PMN infiltration; (iii) reduced epithelial damage; and (iv) reduced corneal bacterial loads. 
     Provided herein is a method of preventing and treating ocular infection comprising a step of treating contact lens prior to wearing the contact lens by a subject with a composition comprising one or more tmytC inhibitors. 
     Also provided is an eye drop dispensing bottle comprising a composition for use in the treatment of prophylaxis of an ocular infection. 
    
    
     
       4. BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-D  Experimentally induced keratitis in NZW rabbits after intrastromal injection of  T. pulmonis -PW 1004.  FIG. 1A : Gross appearance of the rabbit eyes after  Tsukamurella  infection.  FIG. 1B : Mean bacterial load recovered from the cornea of rabbits infected with  T. pulmonis -PW 1004 and those of control rabbits at 24 h PI. Error bars indicated mean CFU/cornea ±SEM of 3 independent experiments.  FIG. 1C : Immunohistochemical staining of corneal sections using mouse anti- T. pulmonis -PW 1004 serum. The boxed area is further enlarged and shown in the right-hand panel of the corresponding image. Strong positive staining in brown color against  T. pulmonis  could be detected in corneal sections from rabbits infected with  T. pulmonis -PW 1004 (top) but not from the mock-infected control rabbits (bottom). The middle panel shows corneal sections from the infected rabbits stained with pre-immune control serum; corneal sections of infected rabbits showing large amount of inflammatory cell infiltration with hematoxylin counterstain (top and middle).  FIG. 1D : MPO activity (U/mg) of the corneal tissues harvested from rabbits. Error bars indicate mean±SEM of 3 independent experiments. 
         FIGS. 2A-C  Antimicrobial efficacies of commercially available contact lens solutions against  Tsukamurella .  FIG. 2A : Mean log reduction of 7 different  Tsukamurella  species and control strain  P. aeruginosa  after the minimum disinfecting time recommended by the corresponding manufacturer according to the test procedures described in the ISO14729 guideline.  FIG. 2B : Antimicrobial efficacies of various concentrations of PHMB (0, 0.0005, 0.001, 0.0025, and 0.005%) against  T. tyrosinosolvens  and  T. pulmonis .  FIG. 2C : Comparison of antimicrobial efficacies of the contact lens solutions of original and modified compositions with addition of PHMB to a final concentration of 0.0025% against 7 different  Tsukamurella  species and control strain  P. aeruginosa , respectively; The horizontal dashed line indicates 3-log reduction of bacteria, suggesting the antimicrobial efficacy of the contact lens solution is considered satisfactory according to the ISO14729 guideline. Error bars indicate means±SEM of 3 independent experiments. 
         FIGS. 3A-C  Treatment efficacy of PHMB in experimentally induced  Tsukamurella  keratitis in rabbits.  FIG. 3A : Representative photos showing the gross appearance of the rabbit eyes inoculated with  T. pulmonis -PW 1004 for 1 day followed by the treatment with 0.02% of PHMB (left) and sterile saline (right) for 3 days, respectively. Rabbit eyes treated with PHMB showed a lower degree of corneal neovascularization and opacity compared with the control rabbits treated with sterile saline.  FIG. 3B : Histological changes of corneal tissues harvested from rabbits treated with sterile saline (top) and PHMB (middle). PMN (shown in blue arrows) infiltration was less pronounced in the PHMB-treated group compared to the mock (saline)-treated group, where the former showed a lower number of neutrophils and capillary formation in the corneal stroma and the corneal epithelium. Corneal sections from rabbits (i.e., mock-infected and mock-treated) included for comparison (bottom).  FIG. 3C : Mean bacterial load recovered from the cornea of  T. pulmonis -PW1004-infected rabbits treated with sterile saline and PHMB, respectively. Error bars indicate mean CFU/cornea±SEM of 3 independent experiments. 
         FIG. 4  Characterization of the 3 tmyt homologs in  Tsukamurella . Locations of the tmytA, tmytB, and tmytC gene in the genome of  T. pulmonis -PW 1004 are indicated. Alignment of the tmyt homologs identified in  T. pulmonis -PW1004,  T. tyrosinosolvens -PW899,  M. tuberculosis  (GenBank accession numbers NP_218321, NP_216402, YP_177694 and YP_178017) and  C. glutamicum  (GenBank accession numbers AAAP23202-AAAP232007). The catalytic triad formed by functional residues Ser125, Asp/Glu229, and His261, which are important for mycolyltransferase activity, are indicated by black, gray, and dark gray boxes, respectively. 
         FIGS. 5A-C  TmytC is a virulence factor of  T. pulmonis .  FIG. 5A : Gross appearance of the rabbit eyes after intrastromal injection of the PW1004-WT and its derivative mutants. The symptoms of keratitis in rabbits infected with PW1004AtmytC appeared less severe with fewer purulent discharges compared to those infected with the PW1004-WT and PW1004-ΔtmytC/ptmytC mutant.  FIG. 5B : Representative images of H&amp;E staining of corneal sections of infected rabbits. PMN (shown in blue arrows) infiltration in corneal stroma and stromal edema was less prominent in PW1004ΔtmytC compared to the PW1004-WT and PW1004-ΔtmytC/ptmytC mutants, showing the disorderly arranged epithelial layer.  FIG. 5C : Mean bacterial load in cornea inoculated with the PW1004-WT, PW1004ΔtmytC, and PW1004-ΔtmytC/ptmytC at day 2 PI. Error bars indicate means±SEM of 3 independent experiments. 
         FIGS. 6A-D  Gross of appearance of rabbits from mock-infected group (i.e., inoculated with plain culture medium). No pathological sign was observed in rabbits inoculated with plain culture medium up to day 3 PI.  FIG. 6A : Day 0.  FIG. 6B : Day 1.  FIG. 6C : Day 2.  FIG. 6D : Day 3. 
         FIGS. 7A-D  Graphical circular maps of the genomes and the distributions of predicted coding sequence function according to COG and SEED subsystems.  FIG. 7A :  T. tyrosinosolvens -PW899.  FIG. 7B :  T. pulmonis -PW 1004. From outside to centre, ring 1 and 2 show protein coding genes on both the forward and reverse strand (colored by COG categories, respectively); ring 3 shows G+C % content plot, and ring 4 shows GC skew, purple indicating negative values and green, positive values; The columns indicate the number of proteins in different  FIG. 7C : COG and  FIG. 7D : SEED subsystems. 
         FIG. 8  Map of p2NIL-GalK 
         FIG. 9  Map of pΔtmytC 
         FIG. 10  Homologous recombination of tmytC using a knock-out construct. 
         FIGS. 11A-E  Characterization of the 3 tmyt homologs in  Tsukamurella .  FIG. 11A : Locations of the tmytA, tmytB, and tmytC gene in the genome of  T. pulmonis -PW1004 are indicated. Alignment of the tmyt homologs identified in  T. pulmonis -PW1004,  T. tyrosinosolvens -PW899 , M. tuberculosis  (GenBank accession numbers NP_218321, NP_216402, YP_177694 and YP_178017) and  C. glutamicum  (GenBank accession numbers AAAP23202-AAAP232007). The catalytic triad formed by functional residues Ser125, Asp/Glu229, and His261, which are important for mycolyltransferase activity, are indicated by black, gray, and dark gray boxes, respectively.  FIG. 11B : Biofilm formed by the PW1004-WT and its derivative mutants when they were cultured under static conditions for 3 days. With the exception of the PW1004ΔtmytC, dense and confluent biofilm was formed as a floating pellicle at the air-liquid interface in PW1004ΔtmytA, PW1004ΔtmytB, PW1004-WT, and tmytC complemented mutant (PW1004ΔtmytC/ptmytC).  FIG. 11C : Quantitation of the biofilm formed by the PW1004-WT and its derivative mutants using crystal violet staining method. The amount of biofilms was significantly reduced in PW1004ΔtmytC compared to the PW1004-WT (P&lt;0.01) and complemented mutant (P&lt;0.05).  FIG. 11D : SEM and  FIG. 11E : confocal microscopy analyses of  Tsukamurella  biofilms cultured under static conditions for 3 days. Representative SEM micrographs of the biofilm formed by the PW1004ΔtmytC was flattened and less structured compared to those formed by the PW1004-WT and complemented mutant. Likewise, biofilms were fixed and stained with SYTO 9 green fluorescent stain prior to confocal microscopy analysis. Representative micrographs comparing biofilm thickness of each  Tsukamurella  strain was measured in different points of each field. The means and standard deviations of 3 independent experiments are shown. 
         FIG. 12  Appearance of the liquid cultures of the PW1004-WT, tmytC knockout and complemented mutants after 48 h incubation at 37° C. in an aerobic environment. A ring of cells (boxed in yellow) adhering at the air-liquid interface was observed in the culture tubes of the PW1004-WT and PW1004ΔtmytC/ptmytC, but not those of PW1004ΔtmytC. In contrast, a large cell pellet (boxed in green) was observed in the culture tube of PW1004ΔtmytC, suggesting its weaker adhesion to plastics. 
         FIGS. 13A-B  Altered adherence to contact lens, biofilm hydrophobicity, and PHMB susceptibility of the tmytC knockout mutant.  FIG. 13A : Adherence of the wild-type and tymtC mutants to contact lenses in vitro as analyzed by CFU counting analysis. The number of bacteria recovered from the contact lenses inoculated with PW1004ΔtmytC was significantly lower compared to those inoculated with the PW1004-WT (P&lt;0.05) and the PW1004ΔtmytC/ptmytC (P&lt;0.05) mutants. Error bars indicated means±SEM of 3 independent experiments.  FIG. 13B : The PW1004ΔtmytC surface was more hydrophilic compared to the PW1004-WT. Droplets of oil or water containing trypan blue were applied to the surface of the biofilm lawn. In the PW1004-WT and tymtC complemented mutant, the oil spread into a thin film over the surface, suggesting that the cell surface was hydrophobic in nature. In contrast, the water droplet continued to spread (i.e., more hydrophilic) and the oil droplet spread less (i.e., less hydrophobic) in the tymtC knockout mutant. 
         FIGS. 14A-K . Structural analysis of mode of binding between ligands and their analogs with  Tsukamurella  tmytC (blue).  FIG. 14A : Phosphonate inhibitor 3a;  FIG. 14B : phosphonate inhibitor 4a;  FIG. 14C : phosphonate inhibitor 5a;  FIG. 14D : phosphonate inhibitor 6a;  FIG. 14E : trehalose;  FIG. 14F : trehalose analog 11a;  FIG. 14G : trehalose analog 15a;  FIG. 14H : trehalose analog 18a;  FIG. 14I : cyclipostins and cyclophostin analog CyC7β;  FIG. 14J : cyclipostins and cyclophostin analog CyC8β;  FIG. 14K : cyclipostins and cyclophostin analog CyC17. 
         FIGS. 15A-E   FIG. 15A : A map of one embodiment of a vector useful for the disclosure p2NIL-GALK vector.  FIGS. 15B-C : Nucleic acid sequence of p2NIL-GALK.  FIG. 15D : Nucleic acid sequence of hsp60 promoter.  FIG. 15E : Nucleic acid sequence of GalK. 
         FIGS. 16A-D   FIG. 16A : A map of one embodiment of the knock-out construct useful for the disclosure pΔtmytC.  FIGS. 16B-D : Nucleic acid sequence of pΔtmytC. 
         FIGS. 17A-B   FIG. 17A : Nucleic acid sequence of the upstream region of tmytC in pΔtmytC.  FIG. 17B : Nucleic acid sequence of a portion of the upstream region of tmytC. 
         FIGS. 18A-B   FIG. 18A : Nucleic acid sequence of the downstream region of tmytC in pΔtmytC.  FIG. 18B : Nucleic acid sequence of a portion of the downstream region of tmytC. 
     
    
    
     4.1 DEFINITIONS 
     As used herein, the term “about” refers to a range of +/−5% of the number that is being modified. 
     As used herein, the term “subject” or “patient” includes either a human or non-human animal, such as a mammal. By “subject” is meant any animal, including horses, dogs, cats, pigs, goats, rabbits, hamsters, monkeys, guinea pigs, rats, mice, lizards, snakes, sheep, cattle, fish, and birds. A human subject may be referred to as a patient. 
     As used herein the term “ocular surface” includes the wet-surfaced and glandular epithelia of the cornea, conjunctiva, lacrimal gland, accessory lacrimal glands, nasolacrimal duct and meibomian gland, and their apical and basal matrices, puncta and adjacent or related structures, including the eyelids linked as a functional system by both continuity of epithelia, by innervation, and the endocrine and immune systems. 
     The term “treat”, “treating”, or “treatment”, with reference to a certain disease condition in a mammal, refers causing a desirable or beneficial effect in the subject having the disease condition. The desirable or beneficial effect may include reduced frequency or severity of one or more symptoms of the disease, or arrest or inhibition of further development of the disease, condition, or disorder. Some laboratory signs that the clinician may observe for response to treatment include normalization of tests. 
     As used herein, “prevention” means that an inoculum of an ocular pathogen introduced to an eye does not develop into a symptomatic ocular infection when the eye is treated with the ophthalmic composition (either before or after introduction of the inoculum), whereas an eye not treated with the ophthalmic composition develops a symptomatic ocular infection. Prevention may be, for example, following surgery, after birth for the newborn, or from accidental contact with contaminating materials. 
     The term “vector” refers to a nucleic acid molecule capable of transporting a foreign nucleic acid molecule. The foreign nucleic acid molecule is linked to the vector nucleic acid molecule by a recombinant technique, such as ligation or recombination. This allows the foreign nucleic acid molecule to be multiplied, selected, further manipulated or expressed in a host cell or organism. A vector can be a plasmid, phage, transposon, cosmid, chromosome, virus, or virion. One type of vectors can be integrated into the genome of a host cell upon introduction into the host cell, and thereby are replicated along with the host genome. 
     As used herein, “virulence” is a pathogen&#39;s or microbe&#39;s ability to infect or caused a diseases state in a host. Virulent is measured by either disease severity or a pathogen&#39;s infectivity. 
     As used herein, “homologous recombination” is the exchange of DNA strands of similar, substantially identical or homologous nucleotide sequence which is one mode of genome modification. 
     As used herein, “homologous recombination construct” is a vector that comprises at least one homologous region that flank a target gene. 
     As used herein, “5′ flanking region” is a homologous sequence at the 5′ or upstream region of a target gene. 
     As used herein, ‘3’ flanking region” is a homologous sequence at the 3′ or downstream region of a target gene. 
     The terms “ocular infection” refers to an infection caused by a microorganism or microorganisms in or around an eye or the eye structure which include the eyelids and lacrimal apparatus, the conjunctiva, the cornea, the uvea, the vitreous body, the retina, and the optic nerve. Ocular infections include bacterial ophthalmic infections, fungal ophthalmic infections and viral ophthalmic infections. 
     The terms “homologous” as used herein denotes a characteristic of a nucleic acid sequence, wherein a nucleic acid sequence has at least about 85 percent to about 95 percent sequence identity, at least about 95 percent sequence identity to about 100 percent sequence identity, as compared to a reference sequence. The percentage of sequence identity is calculated excluding small deletions or additions which total less than 25 percent of the reference sequence. The reference sequence may be a subset of a larger sequence, such as a portion of a gene or flanking sequence, or a repetitive portion of a chromosome. Homologous sequences could be determined by hybridization in an experimental setting which is defined herein as the formation of hybrids between a targeting polynucleotide (e.g., a polynucleotide of the invention which may include substitutions, deletion, and/or additions as compared to the predetermined target DNA sequence) and a predetermined target DNA, wherein the targeting polynucleotide preferentially hybridizes to the predetermined target DNA such that, for example, at least one discrete band can be identified on a Southern blot of DNA prepared from target cells that contain the target DNA sequence, and/or a targeting polynucleotide in an intact nucleus localizes to a discrete chromosomal location characteristic of a unique or repetitive sequence. It is evident that optimal hybridization conditions will vary depending upon the sequence composition and length(s) of the targeting polynucleotide(s) and target(s), and the experimental method selected by the practitioner. Various guidelines may be used to select appropriate hybridization conditions (see, Maniatis et al., Molecular Cloning: A Laboratory Manual (1989), 2nd Ed., Cold Spring Harbor, N.Y. and Berger and Kimmel, Methods in Enzymology, Volume 152, Guide to Molecular Cloning Techniques (1987), Academic Press, Inc., San Diego, Calif., which are incorporated herein by reference. 
     As used herein, “inhibitors” of tmytC refer to modulatory molecules or compounds that, e.g., bind to, partially or totally block activity, decrease, prevent, delay activation, inactivate, desensitize, or down regulate the activity or expression of tmytC protein. In a specific embodiment, an inhibitor specifically inhibits the tmytC described herein. Inhibitors can include siRNA or antisense RNA, genetically modified versions of tmytC protein, e.g., versions with altered activity, as well as naturally occurring and synthetic tmytC antagonists, antibodies, small chemical molecules and the like. TmytC inhibitors for use in the invention can be screened using methods are known in the art. Assays for identifying tmytC inhibitors can be performed in vitro or in vivo, e.g., in cells, or cell membranes, by applying test inhibitor compounds, and then determining the functional effects on activity. 
     In some embodiments, samples or assays comprising tmytC proteins that are treated with a potential inhibitor are compared to control samples without the inhibitor, to examine the effect on activity. Typically, control samples, e.g., cells, that have a wild type tmytC are assigned a relative protein activity value of 100%. Inhibition of tmytC is achieved when the activity value relative to the control is changed at least about 20%, at least about 50%, at least about 75-100%, or more. 
     5.0 DETAILED DESCRIPTION 
       Tsukamurella  is a group of multi-drug resistant bacteria that is associated with various human infections. This previously lesser known group of bacteria has emerged in global scale in recent years and there are escalating cases of  Tsukamurella  infections reported in Europe, Asia, America and Africa.  Tsukamurella  species are commensal bacteria that are widespread in the environment and has been isolated from soil, arthropods, water, sludge foam and sponges. They are also opportunistic pathogens that can be spread through clinical instruments such as catheters.  Tsukamurella  is now increasingly recognized as a cause of bacterial conjunctivitis and keratitis. Moreover, our recent study, based on the largest number of  Tsukamurella  cases, showed that 40% of  Tsukamurella  isolates were recovered from ophthalmological specimens, much higher than that recovered from blood cultures. This indicates that ocular infections are the most important group of disease caused by  Tsukamurella . Notably, cases of  Tsukamurella  keratitis and conjunctivitis have most probably been overlooked in the past because diphtheroidal gram-positive rods recovered from corneal scrapings and eye swabs were either regarded as contaminants or misidentified as other bacteria, such as atypical mycobacteria. In fact, the cause of many cases of conjunctivitis is unknown, likely due to the difficulty in identifying and relating these cases to  Tsukamurella  infection. 
       Tsukamurella  keratitis is also associated with the wearing of contact lenses. As  Tsukamurella  is naturally found in the environment, even detected in drinking water supplies, there is a high risk of infection. However, we have found that common contact lens disinfecting solutions are ineffective against  Tsukamurella . Moreover, previous studies have reported that  Tsukamurella  species are generally resistant to commonly used antibiotic eye drops prescribed for patients with bacterial ocular infections, such as chloramphenicol and tetracycline. Although some strains of  Tsukamurella  are susceptible to levofloxacin, another common antibiotic used in eye drops, we showed, using our rabbit keratitis model, that perforations with severe discharges accompanied by behavioral abnormalities were evident after treatment. There was an increased incidence of corneal perforation in patients after topical fluoroquinolone treatment. Hence, the prevention and therapeutic options for  Tsukamurella -associated ocular infections are rather limited. Also, existing contact lens disinfecting solutions were not effective against many  Tsukamurella  species, such as T.  sinensis, T. hongkongensis, T. ocularis, T. hominis , and  T. spumae . and was unable to meet the ISO14729 stand-alone primary acceptance criteria for disinfecting solutions. 
     Provided herein is a method to reduce virulence of  Tsukamurella  comprising a step of decreasing the expression of tmytC gene wherein the reduction of the virulence is characterized by at least one of: (i) reduced biofilm formation; (ii) reduced adherence property; (iii) reduced polymorphonuclear leukocyte (“PMN”) infiltration; (iv) reduced epithelial damage; and (v) reduced corneal bacterial loads. 
     Genome modification methods are well known in the art. In one embodiment, the expression of tmytC gene is decreased by a knock-out of the tmytC gene. In certain embodiments, the expression of tmytC gene is decreased to 0%-10%, 10%-30%, 30%-50%, 50%-70%, or 70%-90% of the tmytC gene expression as compared to a wild-type  Tsukamurella  that is without genome modification of the tmytC gene. 
     In one embodiment, the expression of tmytC gene is decreased by introducing a construct comprising CRISPR associated system Cas9 nuclease (CRISPR/Cas9). 
     In one embodiment, the expression of tmytC gene is decreased by introducing a homologous recombination construct comprising: (i) a vector comprising a promoter expressing a marker; (ii) a 5′ flanking region of the tmytC gene; (iii) and a 3′ flanking region of the tmytC gene. 
     Provided herein is a homologous recombination construct comprising: (i) a vector comprising a promoter expressing a marker; (ii) a 5′ flanking region of the tmytC gene; (iii) and a 3′ flanking region of the tmytC gene. In one embodiment, the promoter is a hsp60 promoter. In one embodiment, the marker is GalK. In one embodiment, the vector is p2NIL-GalK. In one embodiment, the 5′ flanking region of the tmytC gene is about 200 bp-300 bp, 300 bp-500 bp, 500 bp-800 bp, 800 bp-1200 bp. In one embodiment, the 3′ flanking region of the tmytC gene is about 200 bp-300 bp, 300 bp-500 bp, 500 bp-800 bp, 800 bp-1200 bp. 
     In one embodiment, the construct is pΔtmytC. 
     Provided herein is a modified  Tsukamurella  that does not express tmytC. 
     Provided herein is a method of treating an ocular bacterial infection in a subject, said method comprises a step of administering to the subject a homologous recombination construct comprising: (i) a vector comprising a promoter expressing a marker; (ii) a 5′ flanking region of the tmytC gene; and (iii) a 3′ flanking region of the tmytC gene. 
     In one embodiment, the ocular infection is caused by a multi-drug resistant  Tsukamurella.    
     In one embodiment, the  Tsukamurella  infection is from  T. tyrosinosolvens, T. pulmonis, T. sinensis, T. hongkongensis, T. ocularis, T. hominis, T. spumae  or a combination thereof. 
     In one embodiment, the ocular infection is conjunctivitis, blepharitis and/or keratitis. 
     In one embodiment, the method provides at least a 3-log reduction in infection. 
     In one embodiment, the knock-out construct is pΔtmytC. 
     Provided herein is a method of treating or preventing ocular bacterial infection in a subject comprising a step of administering to the subject a composition comprising one or more tmytC inhibitors. 
     In one embodiment, the ocular bacterial infection is treated or prevented as characterized by at least one of: (i) reduced biofilm formation; (ii) reduced adherence property of the bacteria; (iii) reduced PMN infiltration; (iii) reduced epithelial damage; and (iv) reduced corneal bacterial loads. 
     In one embodiment, the ocular bacterial infection is treated or prevented by a combination therapy. In certain embodiments, the ocular infection may be treated with an anti-inflammatory agent. In certain embodiments, the anti-inflammatory agent comprises a steroidal anti-inflammatory or a non-steroidal anti-inflammatory agent or both. In certain embodiments, the anti-inflammatory agent comprises dexamethasone, diflurprednate, loteprednol, prednisolone acetate, ketotifen fumarate, diclofenac sodium, flurbiprofen sodium, ketorolac tromethamine, suprofen, celecoxib, naproxen, or rofecoxib, or a combination thereof. 
     In certain embodiments, an ophthalmic composition further comprises 0.0025%-0.08% of polyhexamethylene biguanide (“PHMB”), polyquaternium, myristamidopropyl dimethylamine or a combination thereof. In one embodiment, the bacterial infection is caused by a multi-drug resistant bacteria. In one embodiment, the bacterial infection is from  T. tyrosinosolvens, T. pulmonis, T. sinensis, T. hongkongensis, T. ocularis, T. hominis, T. spumae  or a combination thereof. In one embodiment, the bacterial infection is conjunctivitis and/or keratitis. In one embodiment, the method provides for at least a 3-log reduction in infection. The reduction in infection may be measured as disclosed in examples 6.1.2 and 6.4.9. 
     Provided herein is a method of preventing and treating ocular infection comprising a step of treating contact lens prior to wearing the contact lens by a subject with a composition comprising one or more tmytC inhibitors. 
     In one embodiment, the composition further comprises 0.0025%-0.08% of polyhexamethylene biguanide (“PHMB”), polyquaternium and/or myristamidopropyl dimethylamine or a combination thereof. 
     Provided herein is a pharmaceutical composition comprising one or more TmytC inhibitors; and optionally 0.0025%-0.08% of PHMB or myristamidopropyl dimethylamine or a combination thereof. 
     Also provided is an eye drop dispensing bottle comprising a composition for use in the treatment of prophylaxis of an ocular infection 
     Provided herein is a construct with specific 5′ (“upstream”) and 3′ (“downstream sequences”) flanking region of the tmytC gene, which is a  Tsukamurella  mycolyltransferase. The construct allows for the specific deletion of the mycolyltransferase by homologous recombination. The resulting mycolyltransferase deletion mutant is a strain of  Tsukamurella  with greatly reduced virulence. Provided herein is a strain of  Tsukamurella  that does not express tmytC. 
     It was found that the adherence property of  Tsukamurella  to contact lens and abiotic surfaces, such as plastic ware, was significantly reduced in the deletion mutant. The ability to adhere is a key characteristic in biofilm formation, which is an essential factor in the pathogenesis of opportunistic bacteria. Hence, the loss of the ability to form biofilm reduces the ability of the pathogen to cause disease. Secondly, using the rabbit keratitis model, the keratitis symptoms in rabbits infected with the mycolyltransferase deletion mutant was less severe with less purulent discharge compared to those infected with wild type  Tsukamurella . The rabbits infected with the deletion mutant also had a lower degree of PMN infiltration, reduced epithelial damage and significantly lower corneal bacterial loads, indicating greatly reduced virulence. Taken together, by knocking out  Tsukamurella  mycolyltransferase using the deletion construct, the virulence was significantly impacted. 
     Disclosed herein is a construct as a therapeutic strategy for the treatment of  Tsukamurella  keratitis that are important for specialists of different fields including clinicians, biochemists and chemists, ophthalmologists, opticians and scientists. 
     In one aspect, the disclosure provides a method to delete a target gene. In one aspect, the target gene is deleted through homologous recombination. In one aspect, the deletion of the target gene utilizes a homologous recombination construct. In one aspect, the construct comprises two homologous sequences having a length of 100-300, 300-500, 500-800, 800-1,000, 1,000-1,200 nucleotides. The construct comprises a promoter functionally linked to a marker, homologous sequences that are 5′ flanking region and 3′ flanking region of the targeted gene. In one embodiment, the marker is galactokinase (GalK). Galactokinase is a key enzyme of galactose metabolism which phosphorylates D-galactose to generate galactose 1-phospate. The enzyme can also convert 2-deoxy-D-galactose into 2-deoxygalactose-1-phosphate, which is not further metabolized and is toxic to the cell. This marker has been found to be more suitable for  Actinomyces  than other selectable makers. It is noted that one skilled in the art using the disclosure herein could use other recombinant techniques such as CRISPR to delete the target gene. 
       Tsukamurella , a group of multi-drug resistant, Gram-positive, aerobic and partially acid-fast bacteria, are emerging causes of bacterial conjunctivitis and keratitis. We developed a rabbit model of  Tsukamurella  keratitis to dissect its pathogenesis mechanisms and design preventive and treatment strategies. Four common contact lens solutions with the disinfectant, polyhexamethylene biguanide (PHMB), at concentrations 0.0001-0.00013% were ineffective in killing  Tsukamurella , but increasing the concentration of PHMB to 0.0025% largely improved their antimicrobial efficacies against  Tsukamurella . Moreover, 0.02% PHMB was highly effective in treating  Tsukamurella  keratitis in the rabbit model. Using genome sequence data followed by gene deletion and complementation studies, tmytC, encoding a mycolyltransferase, was shown to have an important role in causing  Tsukamurella  keratitis in the rabbit model. This is also the first report demonstrating the novel role of mycolyltransferase in causing ocular infections. Specific inhibitors targeting TmytC, alone or in combination with PHMB, could serve as an armamentarium for the treatment of  Tsukamurella  infections. 
     In certain embodiments, the bacterial infection is caused by a multi-drug resistant and gram-positive, aerobic and partially acid-fact bacteria. In one embodiment, the bacteria is  Tsukamurella . In certain embodiments, the bacteria is  T. tyrosinosolvens -PW899 and  T. pulmonis  PW1004. 
     In certain embodiments, the ocular infection is mediated by mycolyltransferase C (“tmytC”). In certain embodiments, the method further comprises a step of treating the subject with one or more TmytC inhibitors. 
     In certain embodiments, the method provides at least a 3-log reduction of an infection. In certain embodiments, the method provides a 2-log to 3-log reduction of an infection. In certain embodiments, the method provides a 3-log to 4-log reduction of an infection. In certain embodiments, the method provides a 4-log to 5-log reduction of an infection. 
     In certain embodiments, the ophthalmic composition further comprises 0.0025%-0.02% of PHMB. In certain embodiments, the composition comprises 0.0025%-0.005% of PHMB. In certain embodiments, the composition comprises 0.0025-0.003%, 0.003%-0.004%, 0.004%-0.005% of PHMB. In one embodiment, the composition comprises 0.0025% of PHMB. In one embodiment, the composition comprises 0.02% of PHMB. In certain embodiments, the composition comprises 0.02%-0.08% of PHMB. In certain embodiments, the composition comprises 0.02%-0.03%, 0.03-0.04%, 0.04-0.05%, 0.05-0.06%, 0.06-0.07%, 0.07-0.08%, 0.08-0.09%, 0.08-0.1% of PHMB. In certain embodiments, the composition comprises 0.0025%-0.08% of PHMB. 
     In certain embodiments, the composition is administered for 1-2 days, 2-3 days, 3-4 days, 4-5 days, 5-7 days to the subject. 
     In certain embodiments, the ocular disease or infection is of bacterial, mycobacterial, fungal, viral, or amoebal origin. In one embodiment, the infection is caused by  Acanthamoeba.    
     In one embodiment, the composition does not contain levofloxacin. 
     In one embodiment, the composition is a contact lens solution. 
     5.1 Pharmaceutical Composition 
     Pharmaceutically acceptable carrier refers to a pharmaceutically acceptable material, formulation or vehicle, such as a liquid or solid filler, diluent, excipient, solvent or encapsulating material, involved in carrying or transporting the active compound from one organ or portion of the body, to another organ or portion of the body. Each carrier must be “acceptable” in the sense of being compatible with the other components of the composition (e.g., synthetic compound) and not injurious to the subject. Lyophilized compositions, which may be reconstituted and administered, are also within the scope of the present disclosure. 
     Ophthalmic composition may be formulated in any manner suitable for topical administration to an eye of a patient. Numerous suitable topical ophthalmic drug forms are well-known (see, e.g. Baranowski et al., The Scientific World Journal, Vol. 2014, Article ID 861904, incorporated herein by reference). The ophthalmic composition may further comprising an excipient that is a polyvinyl alcohol, polypropylene glycol, a carbomer, polycarbophil, a polyoxyethlene-polyoxypropylene block copolymer, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hyaluronic acid, dextran, chondroitin sulfate, gellan gum, xanthan gum, guar gum, trehalose, tamarind seed polysaccharide, or a cyclodextrin, or any combinations of any two or more of the foregoing excipients. 
     Pharmaceutically acceptable carriers may be, for example, excipients, vehicles, diluents, and combinations thereof. For example, where the compositions are to be administered orally, they may be formulated as tablets, capsules, granules, powders, or syrups; or for parenteral administration, they may be formulated as injections (intramuscular, subcutaneous, intramedullary, intrathecal, intraventricular, intravenous, intravitreal), drop infusion preparations, or suppositories. For application by the ophthalmic mucous membrane route, they may be formulated as eye drops or eye ointments. These compositions can be prepared by conventional means, and, if desired, the active compound may be mixed with any conventional additive, such as an excipient, a binder, a disintegrating agent, a lubricant, a corrigent, a solubilizing agent, a suspension aid, an emulsifying agent, a coating agent, or combinations thereof. 
     It should be understood that the pharmaceutical compositions of the present disclosure can further include additional known therapeutic agents, drugs, modifications of the synthetic compounds into prodrugs, and the like for alleviating, mediating, preventing, and treating the diseases, disorders, and conditions described herein. 
     In one embodiment, the compositions are provided in an aqueous delivery system. Aqueous delivery systems are water-based systems, which can be instilled directly in the eye, or may be used to condition, store, or clean ophthalmic devices which are placed in the ocular environment. Examples of aqueous delivery systems can include one or more of the following: packing solutions, storing solutions, cleaning and care solutions, multipurpose solutions, conditioning solution and ophthalmic drops. The aqueous delivery systems may also include known components, such as one or more of emulsifiers, chelating agents, or stabilizers, surfactants, wetting agents, antioxidants, tonicity adjusting agents, preservatives, osmoprotection agents, combinations thereof, and the like. In certain embodiments, the compositions may be formulated as 0.01 to 2.0 percent by weight solutions in water at a pH of 4.5 to 8.0. 
     The packaging solution may be any water-based solution including that which is used for the storage of contact lenses. The compositions are dispersed in the packaging solution. Typical solutions include, without limitation, saline solutions, other buffered solutions, and deionized water. The preferred aqueous solution is saline solution containing salts including, without limitation, sodium chloride, sodium borate, sodium phosphate, sodium hydrogenphosphate, sodium dihydrogenphosphate, or the corresponding potassium salts of the same. These ingredients are generally combined to form buffered solutions that include an acid and its conjugate base, so that addition of acids and bases cause only a relatively small change in pH. The buffered solutions may additionally include citric acid, sodium citrate, sodium carbonate, sodium bicarbonate, acetic acid, sodium acetate, and the like and combinations thereof. Preferably, the solution is a borate buffered or phosphate buffered saline solution. 
     To form the packaging solution, at least one surfactant or emulsifier along with any additional ingredients are combined with the water-based solution, stirred, and dissolved or dispersed. The pH of the solution preferably is adjusted to about 6.2 to about 7.5. The lens to be stored in the packaging solution of the invention is immersed in the solution and the solution and lens placed in the package in which the lens is to be stored. Alternatively, the solution may be placed into the package and the lens then placed into the solution. Typically, the package is then sealed by any convenient method, such as by heat sealing, and undergoes a suitable sterilization procedure. 
     The surfactants suitable for use in the disclosure are of any suitable molecular weight, preferably about 200 to about 1,000,000, more preferably about 1000 to about 18,000. Useful surfactants have a hydrophile-lipophile balance (“HLB”) of about 10 to about 30, preferably about 15 to about 25, more preferably about 15 to about 23. 
     Any of the known surfactants fitting the aforementioned criteria may be used provided that the surfactant is compatible, in terms of solubility, in the solution with which it is used. Thus, suitable surfactants include, without limitation, cationic, ionic, non-ionic surfactants, and combinations thereof. However, the use of a lens packaging solution containing cationic and ionic surfactants may cause eye irritation. 
     Suitable non-ionic surfactants include, without limitation, polyethylene glycol esters of fatty acids, such as polysorbate 20, 60 or 80, all available as TWEEN® surfactants, alkanolamides, amine oxides, ethoxylated alcohols and acids, and surfactants having one or more poly(oxyalkylene) chains, such as poloxamine surfactants (a surface-active agent that removes lipid and environmental debris from the lenses; polyalkoxylated block polymers of ethylene diamine) or poloxamer surfactants (any of a series of nonionic surfactants of the polyoxypropylene-polyoxyethylene copolymer type, used as surfactants, emulsifiers, stabilizers, and food additives), and the like, and combinations thereof. 
     The surfactant may be combined with any known active and carrier components useful for lens packaging solution or for a rewetting drop. Suitable active ingredients for lens packaging solutions include, without limitation, antibacterial agents, anti-dryness agents, such as polyvinyl alcohol, polyvinylpyrrolidone, and dextran, tonicity agents, and the like, and combinations thereof. 
     Suitable wetting agents, along with viscosity enhancers include, without limitation: methyl gluceth-20 (sold under the trade name, for example, Glucam E20), carboxymethylcellulose, dextran 70, gelatin, hydroxymethylcellulose, hydroxypropyl methylcellulose, hydroxypropylethylcellulose, hydroxypropyl cellulose, methylcellulose, PEG, propylene glycol, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), Carbomer, polymethylvinylethermaleic anhydride, hyaluronic acid, xanthan gum, and polyacrylicacid. 
     Suitable antioxidants used in this disclosure include, without limitation, hindered phenols, catechols, tocopherols, carotenoids, hyaluronic acid, lutein, or any species that can scavenge free radicals. Antioxidants are molecular species that inhibit oxidative damage of other chemicals through redox chemical reactions. These reactions typically transfer electrons for a molecule species to an oxidant molecule. These can include free radicals, which can cause chain reactions. In simplest terms, antioxidants are reducing agents. Examples of antioxidants include, without limitation: Vitamin E, Vitamin C, beta carotene (which is converted to Vitamin A), and peroxidases, and other agents which can inhibit the formation of free radicals, e.g., chelating agent, EDTA, diethylene triamine pentaacetic acid (DTPA), N, N-bis[carboxymethyl]glycine (NTA), and the like. 
     In some embodiments, Vitamin E is added to a composition. In one embodiment, the compositions are hydrolytically stable at neutral pH, and do not hydrolyze during storage in the pH neutral ophthalmic composition and sterile preparations. This means that the ophthalmic solutions and sterile preparations do not cause stinging when instilled in the eye. In some embodiments, the topical application of a composition comprising is an effective therapeutic strategy to decrease ocular surface infection. As discussed herein the infection of the ocular surface can be seen in, for example, both anterior segment/front of the eye conditions and back of the eye conditions. In one embodiment, the disclosed method improves the interaction between the lens and the tear film and/or the lids. 
     5.2 Effective Dose 
     A therapeutically effective amount of the composition disclosed herein is an amount effective to produce a clinically recognizable favorable change in the pathology of the disease or condition being treated. A therapeutically effective amount includes those effective to treat, reduce, alleviate, ameliorate, mitigate, eliminate or prevent one or more symptoms of the ocular conditions sought to be treated or the condition sought to be avoided or treated. One of skill in the art would readily be able to determine what is a therapeutically effective amount or an effective amount. Suitable dosages of the composition for use in the methods of the present disclosure will depend upon a number of factors including, for example, age and weight of an individual, severity of ocular disease, specific composition to be used, nature of a composition, route of administration and combinations thereof. Ultimately, a suitable dosage can be readily determined by one skilled in the art such as, for example, a physician, a veterinarian, a scientist, and other medical and research professionals. For example, one skilled in the art can begin with a low dosage that can be increased until reaching the desired treatment outcome or result. Alternatively, one skilled in the art can begin with a high dosage that can be decreased until reaching a minimum dosage needed to achieve the desired treatment outcome or result. 
     In one particularly suitable embodiment, the composition is administered in a dosage ranging from about 0.1 μg to about 300 mg. In one particularly suitable embodiment, the composition is administered oral as a tablet or capsule once a day. Administration of an effective amount of the composition may be by a single dose, multiple doses, as part of a dosage regimen, and combinations thereof as determined by those skilled in the art for the relevant mechanism or process. The dosage regimen may vary depending on the symptoms, age and body weight of the subject, the nature and severity of the disorder to be treated or prevented, the route of administration and the form of the drug. In one embodiment, the composition is administered via intravitreal injection to the subject and is administered once a month. In another embodiment, the composition is administered via eye drop or eye ointment to the subject and is administered once a day. In yet another embodiment, the composition is administered via eye drop or eye ointment to the subject and is administered twice a day. 
     In certain embodiments, the compositions of the present disclosure may be administered topically on the eye. The dosage range may be about 0.001 mg to about 5.0 mg/per eye. In one aspect, the dosage for one eye may be about one drop of solution which corresponds to about 50 μl to about 80 μl of solution. 
     In certain embodiments, the composition may be topically applied by placing one to two drops, or more, in each eye 1 to 24 times daily. For example, the composition may be applied 1, 2, 3, 4 or 8, 12, 18 or 24 times a day, or more. In an embodiment, a composition of the present disclosure is topically applied by placing one to two drops in each eye once or twice daily. 
     In certain embodiments, the ophthalmic compositions can also be tested in a selected animal model. 
     5.3 Methods of Treatment 
     The disclosed composition can also be administered to a subject that has been identified in need thereof as described herein. The subject can be suffering or having ocular infections. One in skill in the art would know how to identify the subject in need of a treatment for ocular infections. 
     Provided herein is a treatment of an ocular infection when the ophthalmic composition is administered to an eye of a subject, or the prevention of an ocular infection when the ophthalmic composition is administered to an eye of a patient before or after the introduction of an inoculum of an ocular pathogen. The method disclosed herein is effective to treat or prevent infection following an ophthalmic surgery or an ophthalmic procedure. 
     The present disclosure can also be administered to a subject to mitigate at least one sign and/or symptom of ocular infection. 
     When the disclosed composition is loaded onto a contact lens for delivery to the eye during contact lens wear, the composition can be held on to the eye via the contact lens long enough to be delivered efficiently to the eye in order provide relief to individuals suffering from ocular infection. 
     In one aspect of the disclosure, a method is provided for administering a nucleic acid to a pathogen that causes ocular infection in a subject. An amount of a composition is administered to an eye of the subject where the pathogen is present. The composition comprises a vehicle that carries the homologous recombination construct to reduces the expression of a gene in the pathogen. These aspects and others which will be apparent to those of skill in the art upon reading the specification provide the art with a method of treating ocular disorders without causing appreciable damage to the eye. 
     In one embodiment, the homologous recombination construct is delivered to the bacteria at the site of bacterial infection where the construct is packaged into a bacteriophage. The phage attaches to a bacterium and injects the genetic material into the bacterial cytoplasm. One skilled in the art knows the genome-editing potential of bacteriophage as described in Pennisi E. 2020 Science doi:10.1126/science “Microbes-mystery-dna-helps-defeat-viruses-and-has-genome-editing-potential”. The bacteriophage carrying the construct can be administered in the form of eye drops, contact lens solution or additive which may allow therapeutic and potential prophylactic uses of the phage against the bacteria. In one embodiment, the homologous recombination construct is delivered to the bacteria at the site of bacterial infection where the construct is packaged into a nanoparticle. 
     5.4 Genome Modification 
     Recent advances in genome engineering have enabled the manipulation and/or introduction of virtually any gene across a diverse range of cell types and organisms. In particular, the advent of site-specific designer nucleases has enabled site-specific genetic modifications by introducing targeted breaks into a host cell genome, i.e., genome editing. These nucleases include zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and clustered regulatory interspaced short palindromic repeats CRISPR/Cas (CRISPR-associated)-based RNA-guided endonucleases. ZFNs have been utilized, inter alia, to modify target loci in crops (Wright et al., Plant J 44:693-705 (2005)), to improve mammalian cell culture lines expressing therapeutic antibodies (Malphettes et al., Biotechnol Bioeng 106(5):774-783 (2010)), and to edit the human genome to evoke resistance to HIV (Urnov et al., Nat Rev Genet 11(9):636-646 (2010)). Similarly, TALENs have been utilized to modify a variety of genomes, including those of crop plants (Li, et al., Nat. Biotechnol. 30: 390-392 (2012)), human, cattle, and mouse (Xu et al., Molecular Therapy Nucleic Acids 2, el 12 (2013)). More recently, CRISPRs have been successfully utilized to edit the genomes of bacteria (e.g., Jiang et al., Nature Biotechnology 31(3):233-239 (2013); Qi et al., Cell, 5, 1173-1183 (2013); yeast (e.g., DiCarlo et al., Nucleic Acids Res., 7, 4336-4343 (2013)); zebrafish (e.g. Hwang et al., Nat. Biotechnol., 3, 227-229(2013)); fruit flies (e.g., Gratz et al., Genetics, 194, 1029-1035 (2013)); human cells (e.g., Cong et al., Science 6121, 819-823, (2013); Mali et al., Science, 6121, 823-826 (2013); Cho et al., Nat. Biotechnol., 3, 230-232 (2013)); and plants (e.g., Jiang et al., Nucleic Acids Research 41(20):e188 (2013)); Belhaj et al., Plant Methods 9(39) (2013)). 
     In one embodiment, the treatment and prevention of the ocular infection may be carried out using various gene targeting methods. In one embodiment, bacterial genome disclosed herein is modified by homologous recombination or knock-out which is the exchange of homologous segments along a length of two nucleic acid molecules. In one embodiment, provided herein are methods of integrating exogenous nucleic acids in the form of a construct with a selectable marker into a selected target sites of a host cell genome. In certain embodiments, the methods comprise contacting the host cell genome, e.g. bacterial host cell genome, with a construct comprising an exogenous nucleic acid to undergo a homologous recombination and further comprises selecting a host cell that expresses the selectable marker. This results in the target gene being knocked-out or rendered not functional. 
     The methods and techniques of the present disclosure are generally performed according to methods well known in the art and as described in various general and more specific references that are cited and discussed throughout the present specification unless otherwise indicated. Such references include, e.g., Sambrook and Russell, Molecular Cloning, A Laboratory Approach, Cold Spring Harbor Press, Cold Spring Harbor, N.Y. (2001), Ausubel et al., Current Protocols in Molecular Biology, John Wiley &amp; Sons, NY (2002), and Harlow and Lane Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (1990). Enzymatic reactions and purification techniques are performed according to manufacturer&#39;s specifications, as commonly accomplished in the art or as described herein. The nomenclatures used in connection with, and the laboratory procedures and techniques of, analytical chemistry, synthetic organic chemistry, and medicinal and pharmaceutical chemistry described herein are those well-known and commonly used in the art. Standard techniques are used for chemical syntheses, chemical analyses, pharmaceutical preparation, formulation, and delivery, and treatment of patients. 
     Various functions and advantages of these and other embodiments of the present disclosure will be more fully understood from the examples shown below. The examples are intended to illustrate the benefits of the present disclosure, but do not exemplify the full scope of the disclosure. 
     6. EXAMPLES 
     6.1 Results 
     6.1.1. Rabbit model of  Tsukamurella  keratitis. To understand the pathogenesis of  Tsukamurella  keratitis, we developed an eye infection model using New Zealand White (NZW) rabbits. We inoculated  T. pulmonis -PW 1004 at 10 6  colony-forming units (CFUs)/cornea by direct intrastromal injection and the pathological changes of the infected rabbit eyes were monitored daily. At 24 hours (h) post-infection (PI), the rabbit corneas started to develop gross pathological signs of infection, including severe iritis, ocular discharge, corneal infiltrate, corneal erosions and dense corneal opacity, with increasing severity observed over time ( FIG. 1A ). On the other hand, we did not observe any pathological signs in control rabbits injected with plain culture medium only (Supplementary  FIG. 1 ). At 24 h PI, pure cultures of  Tsukamurella  at 6.64±0.46 log CFU/cornea were recovered from the infected rabbits ( FIG. 1B ). Active infection was confirmed by the detection of  T. pulmonis -PW 1004 antigens by immunohistochemical staining using specific anti- T. pulmonis  antibodies. Strong staining against  T. pulmonis  could be detected in corneal sections from rabbits infected with  T. pulmonis -PW1004 (top,  FIG. 1C ) but not from the control rabbits (bottom,  FIG. 1C ). Specificity of the anti- T. pulmonis  antibodies was verified by staining the corneal sections using mouse pre-immune control serum (middle,  FIG. 1C ). Large amount of inflammatory cell infiltraiton was observed with the hematoxylin counterstain in the corneal sections from the  T. pulmonis -infected rabbits (top and middle,  FIG. 1C ). This was in line with the results of the myeloperoxidase (MPO) activity assay, which quantified tissue polymorphonuclear leukocyte (PMN) accumulation. MPO activities increased to 3.87±0.26 U/mg in the corneal homogenates from rabbits infected with  T. pulmonis -PW1004 compared to those from rabbits of the control group ( FIG. 1D ). To fulfill the Koch&#39;s postulates, we used  T. pulmonis -PW 1004 recovered from the cornea of a rabbit to infect other rabbits using the same route of inoculation. Results consistently showed that the infected rabbit developed similar signs and symptoms of keratitis and histopathological changes at 24 h PI. 
     6.1.2 Antimicrobial efficacies of contact lens solutions against  Tsukamurella . Contact lens wear is one of the leading risk factors for bacterial keratitis, and indeed some of the patients with  Tsukamurella  keratitis had histories of contact lens wear 5,11 . We attempted to examine the antimicrobial efficacies of contact lens solutions commonly available in the market against different clinically important  Tsukamurella  species ( T. tyrosinosolvens, T. pulmonis, T. sinensis, T. hongkongensis, T. ocularis, T. hominis , and  T. spumae ) (Table 1), based on the test procedures described in the International Organization for Standardization (ISO) 14729 guidelines 13 . According to the guideline, the contact lens solution is considered effective if it can reduce the starting concentration of bacteria by 3-log at the minimum disinfecting time recommended by the manufacturer (Table 1). Results showed that the 4 tested contact lens solutions demonstrated good efficacies (&gt;5-log reduction) against the control strain  P. aeruginosa  ATCC27853, but the solutions only achieved 0.27±0.16- to 1.34±0.01-log reductions for the  Tsukamurella  species ( FIG. 2A ). These results suggested that the formulation components of these contact lens solutions were not effective against  Tsukamurella  species and was unable to meet the ISO14729 stand-alone primary acceptance criteria for disinfecting solutions. 
     6.1.3 Antimicrobial efficacies of PHMB against  Tsukamurella . PHMB is one of the main antibacterial agents commonly found in contact lens solutions and has been successfully used for the treatment of  Nocardia  and  Acanthamoeba keratitis   14,15 . Three of the 4 contact lens solutions tested in the study also contained PHMB, with concentrations ranging from 0.0001 to 0.00013% (Table 1). We speculated that by increasing the amount of PHMB in these contact lens solutions, the efficacy of these solutions against  Tsukamurella  may be improved. Therefore, the in vitro susceptibility of  T. pulmonis -PW 1004 to a series of PHMB concentrations (0, 0.0005, 0.001, 0.0025, and 0.005%) was preliminary tested using the disk diffusion method. Zones of inhibition were evident at PHMB concentrations of 0.0025% and 0.005% (Table 2). This increased susceptibility of  Tsukamurella  to PHMB was further demonstrated using  T. pulmonis -PW1004 and  T. tyrosinosolvens -PW899. By performing in vitro susceptibility testing according to ISO14729, we found that 0.0025%, but not 0.0005% or 0.001%, of PHMB could achieve 3-log reductions in the 2  Tsukamurella  species ( FIG. 2B ). However, bacterial numbers could not be further reduced by increasing the concentration to 0.005% ( FIG. 2B ). Therefore, antimicrobial efficacy of the 4 contact lens solutions against  Tsukamurella  was tested again by adjusting the final concentrations of PHMB to 0.0025%. Results showed that all the solutions were capable of achieving 3-log reductions for all tested  Tsukamurella  strains ( FIG. 2C ), suggesting that 0.0025% PHMB may be the optimal concentration against  Tsukamurella  in vitro. 
     6.1.4 Treatment of experimental  Tsukamurella  keratitis using PHMB or levofloxacin in rabbits. Chloramphenicol and levofloxacin are common eye drops prescribed for patients with bacterial ocular infections. Since  Tsukamurella  species are generally resistant to chloramphenicol 3,12 , we attempted to study the treatment efficacy of 0.5% levofloxacin and 0.02% PHMB for  Tsukamurella  keratitis using the rabbit model. Twelve rabbits were divided into 3 groups, with each group containing 4 rabbits, and were infected intrastromally with  T. pulmonis -PW 1004 as described previously. Treatment was started at 24 h PI when the typical symptoms of keratitis, with stromal infiltrates on corneal surface, corneal neovascularization and opacity, and sticky yellowish-white discharges were evident. One group of rabbits was treated with sterile saline, while the other two groups were treated with 0.5% levofloxacin and 0.02% PHMB respectively, following the treatment regimens as described in previous studies 16,17 . For the rabbits treated with 0.5% levofloxacin, corneal perforations with severe discharges accompanied by behavioral abnormalities were evident after treatment for 2 days. The rabbits were sacrificed and the experiment discontinued. On the other hand, keratitis symptoms became less severe in rabbits after treatment with 0.02% PHMB for 3 days, with the gross appearance showing a lower degree of corneal neovascularization and opacity compared to control rabbits ( FIG. 3A ). Consistently, histological examination revealed a lower degree of stromal edema as well as capillary formation in the PHMB-treated rabbits ( FIG. 3B ). PMN infiltration was also less evident in this treatment group, in which the number of neutrophils was lower in the corneal stroma and the corneal epithelium ( FIG. 3B ). The number of bacteria recovered from rabbits treated with PHMB was significantly lower compared to the control rabbits treated with saline (3.58±0.49 log vs 1.05±0.07 log, P&lt;0.01,  FIG. 3C ). Unlike the rabbits treated with levofloxacin, we did not observe corneal perforation in rabbits treated with PHMB throughout the whole course of treatment. These results suggest that topical application of 0.02% PMHB demonstrated good efficacy against  Tsukamurella  keratitis without apparent toxicity, making it a potential choice for the treatment of this infection. 
     6.1.5 Genome sequencing and analysis of  T. tyrosinosolvens -PW899 and  T. pulmonis -PW1004. The present rabbit model confirmed the causal relationship between  Tsukamurella  and keratitis, yet the pathogenesis of  Tsukamurella  remained unknown. We attempted to sequence  Tsukamurella  genomes to identify potential virulence factors associated with  Tsukamurella -mediated ocular infections. The draft genomes of  T. tyrosinosolvens -PW899 and  T. pulmonis -PW1004, 2 strains previously isolated from patients with ocular infections 5,6 , were sequenced and assembled ( FIGS. 7A and 7B ). Sequencing generated 11-15 million paired-end reads per strain (estimated 410-540× coverage). After de novo assembly, the draft genome of  T. tyrosinosolvens -PW899 was 4.88 Mb in length distributed in 307 contigs (&gt;500 bp), and that of  T. pulmonis -PW1004 was 4.60 Mb in length distributed in 245 contigs (&gt;500 bp) (GenBank accession numbers of  T. tyrosinosolvens -PW899 and  T. pulmonis -PW1004 are QPKD00000000 and QQQF00000000, respectively) (Table 3). All contigs generated were submitted to the RAST version 2.0 (Rapid Annotation using Subsystem Technology) annotation server, resulting in 4,558 protein-coding sequences (CDSs), 3 rRNA operons and 49 tRNA-encoding genes for  T. tyrosinosolvens -PW899 and 4,241 CDSs, and 3 rRNA operons, and 47 tRNA-encoding genes for  T. pulmonis -PW 1004 (Table 3). Each CDS in the 2 genomes was further classified into different categories in Clusters of Orthologous Groups of proteins (COGs) ( FIG. 7C ) and subsystems in RAST ( FIG. 7D ) based on their predicted functional roles. Specifically, the two  Tsukamurella  genomes contained a number of putative genes that may be involved in pathogenesis (Table 4). Among these, 3 homologs of a gene encoding mycolyltransferase were identified in both genomes of  T. tyrosinosolvens -PW899 and  T. pulmonis -PW1004. Previous studies have shown that proteins which possess mycolyltransferase activities play significant roles in various important biological roles, in members of Corynebacteriales 18,19 . For this reason, we attempted to study the role of these homologs and in the pathogenesis of  Tsukamurella  keratitis. 
     The 3 mycolyltransferase-encoding homologs identified in both  Tsukamurella  genomes were designated as tmytA ( Tsukamurella  mycolyltransferase A), tmytB and tmytC respectively ( FIG. 4 ). The size of the 3 mycolyltransferase homologs varied from 963 to 1,632 bp, as a result of the lack of a C-terminal region in tmytB and tmytC. Their N-terminal regions in  T. tyrosinosolvens -PW899 and  T. pulmonis -PW1004 shared 38.1-68.9% and 38.9-69.6% amino acid (aa) identities respectively ( FIG. 4 ). Phylogenetically, they were most closely related to the mycolyltransferase of  Williamsia limnetica , also a member of Corynebacteriales, sharing 44-45% aa identities. Detailed annotation of the gene sequences revealed the presence of critical aa residues Ser-125, Asp/Glu-229 and His-261 in their N-terminal regions, which forms a catalytic triad ( FIG. 4 ). This is a typical feature of other characterized mycolyltransferases and is essential for mycolyltransferase activityl 9-22.  To further characterize the functional role of the mycolyltransferase homologs in  Tsukamurella , individual knockout mutant strains (PW1004ΔtmytA, PW1004ΔtmytB and PW1004ΔtmytC) were constructed respectively in  T. pulmonis -PW 1004. 
     6.1.6 Reduced virulence in tmytC knockout mutant in rabbits. We hypothesized that tmytC encoding protein is one of the major factors contributing to bacterial virulence in  Tsukamurella  keratitis. Therefore, we examined the importance of TmytC in the pathogenesis of  Tsukamurella  keratitis in vivo by inoculating rabbit corneas with PW1004-WT, PW1004ΔtmytC and PW1004ΔtmytC/ptmytC respectively via intrastromal injection. The keratitis symptoms in rabbits infected with PW1004ΔtmytC were less severe with less purulent discharge compared to those infected with PW1004-WT and PW1004ΔtmytC/ptmytC ( FIG. 5A ). On day 2 PI, the rabbits were sacrificed and their corneas harvested for histopathological studies and bacterial counts. Consistent to the gross appearance of the eyes ( FIG. 5A ), histopathological examination of the corneal tissues revealed a lower degree of polymorphonuclear leukocyte (“PMN”) infiltration in rabbits infected with PW1004ΔtmytC as compared to PW1004-WT and PW1004ΔtmytC/ptmytC, where PMN infiltration was apparent in corneal stroma and stromal edema was prominent ( FIG. 5B ). In addition, PW1004-WT and PW1004ΔtmytC/ptmytC showed a disordered arrangement of the epithelial layer with focal loss of superficial epithelial cells, and shrinkage of the Bowman&#39;s membrane ( FIG. 5B ). Such damages were minimally apparent in PW1004ΔtmytC and absent in the normal corneal sections ( FIG. 5B ). Moreover, the corneal bacterial loads of PW1004-WT and PW1004ΔtmytC/ptmytC were significantly higher than that of PW1004ΔtmytC (P&lt;0.05), which showed only about 5% recovery rate on day 2 PI ( FIG. 5C ). Taken together, these results suggested that TmytC contributes to the pathogenesis of  Tsukamurella  keratitis using in vivo rabbit model. 
     6.1.7 Identification of mycolyltransferase homologs. 
     The 3 mycolyltransferase-encoding homologs identified in both  Tsukamurella  genomes were designated as tmytA ( Tsukamurella  mycolyltransferase A), tmytB and tmytC respectively ( FIG. 11A ). The size of the 3 mycolyltransferase homologs varied from 963 to 1,632 bp, as a result of the lack of a C-terminal region in tmytB and tmytC. Their N-terminal regions in  T. tyrosinosolvens -PW899 and  T. pulmonis -PW1004 shared 38.1-68.9% and 38.9-69.6% amino acid (aa) identities respectively ( FIG. 11A ). Phylogenetically, they were most closely related to the mycolyltransferase of  Williamsia limnetica , also a member of Corynebacteriales, sharing 44-45% aa identities. Detailed annotation of the gene sequences revealed the presence of critical aa residues Ser-125, Asp/Glu-229 and His-261 in their N-terminal regions, which forms a catalytic triad ( FIG. 11A ). This is a typical feature of other characterized mycolyltransferases and is essential for mycolyltransferase activity. To further characterize the functional role of the mycolyltransferase homologs in  Tsukamurella , individual knockout mutant strains (PW1004ΔtmytA, PW1004ΔtmytB and PW1004ΔtmytC) were constructed respectively in  T. pulmonis -PW1004. Biofilm phenotypes in vitro and virulence in vivo of each mutant strain were studied and compared to those of wild-type and/or complemented strains. 
     6.1.8 Characterization of Biofilm Phenotypes in Wild-Type PW1004 and the 3 Tmyt Knockout Mutants 
     Non-polar deletions of tmytA, tmytB, and tmytC respectively were successfully constructed in  T. pulmonis -PW1004. We hypothesized that knockout of the tymt gene may impair biofilm formation in  Tsukamurella . To investigate this, the wild-type and 3 tymt knockout mutants of  T. pulmonis -PW1004 were cultured under static conditions to allow the formation of biofilms. Results showed that dense and confluent biofilms were formed as a floating pellicle at the air-liquid interface in PW1004ΔtmytA, PW1004ΔtmytB, and wild-type PW1004 (PW1004-WT), whereas less textured and reticulated biofilms were formed in PW1004ΔtmytC ( FIG. 11B ). Biofilm quantification using the crystal violet staining method showed that the amount of biofilms was significantly reduced in PW1004ΔtmytC compared to PW1004-WT (P&lt;0.01), while PW1004ΔtmytA and PW1004ΔtmytB produced similar levels of biofilm as PW1004-WT ( FIG. 11C ). To rule out the possibility that knockout of tmyt genes may alter growth kinetics and hence biofilm formation, we measured the growth kinetics of the wild-type and knockout mutants and found that there was no significant difference between the growth rates of the wild-type and knockout mutants. To confirm the importance of TmytC in  T. pulmonis  biofilm formation, we transformed a TmytC expression plasmid (pNV18-tmytC) into PW1004ΔtmytC and studied the subsequent biofilm characteristics. Results showed that PW1004ΔtmytC complemented with TmytC (PW1004ΔtmytC/ptmytC) restored the biofilm phenotype with biofilm quantity levels similar to that of PW1004-WT ( FIG. 11B , C). Independently, we performed a scanning electron microscopy (SEM) analysis to study the biofilm structure of WT, tmytC-knockout and complemented PW1004. Results showed that the biofilm formed by PW1004-WT was highly structured. Deletion of the tmytC gene, however, resulted in the formation of flatter and less structured biofilms (middle,  FIG. 11D ), whereas PW1004ΔtmytC/ptmytC complemented mutant displayed similar biofilm phenotypes as PW1004-WT. The results were further supported by confocal microscopy analysis, in which optical sectioning along the Z axis showed reduced biofilm formation with an average thickness of 20.63±3.00 μm in PW1004ΔtmytC compared to those of 31.17±4.33 μm and 28.08±3.25 μm in the wild-type and complemented mutant, respectively (P&lt;0.001), with no significant difference in the thickness of the biofilm formed between the wild-type and complemented mutant ( FIG. 11E ). Collectively, the results supported that deletion of tmytC gene, but not tmytA or tmytB genes, perturbed the biofilm-forming capacity of  T. pulmonis -PW1004, suggesting that mycolyltransferase contributes significantly to biofilm formation in  T. pulmonis.    
     6.1.9 Reduced Bacterial Adhesion on Contact Lens in tmytC Knockout Mutant 
     Adhesion ability is a key characteristic related to biofilm formation. Since there was an apparent change in the biofilm phenotypes and impaired biofilm formation capacity of PW1004ΔtmytC ( FIG. 1B-E ), we speculated that  Tsukamurella  adherence to abiotic materials, such as contact lenses, may also be altered. Therefore, the adhesion ability of PW1004-WT, PW1004ΔtmytC and PW1004ΔtmytC/ptmytC to contact lenses was determined quantitatively. Results showed that initially all three strains were able to form a thin layer of cells over the entire surface of the contact lens. However, after subsequent mechanical detachment, washing and re-culturing, the number of bacteria recovered from the contact lenses inoculated with PW1004ΔtmytC (3.62±0.17 log CFU) was significantly lower compared to those inoculated with PW1004-WT (5.46±0.05 log CFU) and PW1004ΔtmytC/ptmytC (5.13±0.19 log CFU), respectively (P&lt;0.05) ( FIG. 12A ). Consistently, during the culturing process of the three bacterial strains, a ring of cells adhering to the air-liquid interface was observed in the culture tubes of PW1004-WT and PW1004ΔtmytC/ptmytC, but not PW1004ΔtmytC ( FIG. 12 ). In contrast to PW1004-WT and PW1004ΔtmytC/ptmytC, a large cell pellet was observed at the bottom of the culture tube of PW1004ΔtmytC ( FIG. 12 ), implicating its weaker adhesion to plastic tubes. Collectively, these results demonstrated that the tmytC knockout mutant possessed reduced adhesion ability to contact lenses and abiotic surface (i.e., plastic culture tube), suggesting that TmytC played a role in the adherence of  Tsukamurella  to abiotic surfaces in vitro. 
     6.1.10 Decreased Cell Surface Hydrophobicity in the tmytC Knockout Mutant 
     In addition to adhesion ability, cell surface hydrophobicity is another characteristic related to biofilm formation. The reduced adhesion ability previously observed for the PW1004ΔtmytC mutant ( FIGS. 12 and 13A ) prompted us to study the cell surface hydrophobicity in the wild-type and mutants using a visualization experiment as described previously. This experiment involves adding a drop of water or oil onto the biofilm culture. If the culture cell surface is hydrophobic in nature, the water will form a bead and the oil will spread over the surface, as observed for the wild-type strain (left,  FIG. 13B ). On the other hand, altered cell surface hydrophobicity was clearly shown in the PW1004ΔtmytC biofilm, in which the drop of water spread out more (i.e., more hydrophilic), while oil spread out less (i.e., less hydrophobic) (middle,  FIG. 13B ), compared to the wild-type. The biofilm hydrophobicity of the complemented mutant was restored to a comparable level as observed in the wild-type (right,  FIG. 13B ). These observations indicated that TmytC also contributed to the cell surface hydrophobicity of  T. pulmonis.    
     6.1.11 Docking Analysis Study of  Tsukamurella  Mycolyltransferase tmytC with Ligands and their Analogs 
     As disclosed herein is that tmytC, which encodes for a mycolyltransferase in  Tsukamurella , plays an important role in the pathogenesis of  Tsukamurella  keratitis. Using a rabbit keratitis model, the virulence and survival of  Tsukamurella  was reduced when tmytC was deleted. Moreover, keratitis symptoms were less severe and bacterial loads were significantly lower compared to infection with wild-type  Tsukamurella . tmytC is a target for the treatment of  Tsukamurella  keratitis. Substrate preference and/or spatial cellular localization of the mycolyltransferase is important in the pathogenesis of  Tsukamurella  keratitis. Structural and docking analysis studies were performed to screen for binding molecules of the mycolyltransferase and to design specific inhibitors to target this gene. 
     A variety of ligands and their analogs, that are known to or have potential to bind to mycolic acid containing bacteria, were chosen for their ability to bind to TmytC of  Tsukamurella  PW1004 using Phyre2 and AutoDockTools (Kelley et al. 2015 Nat Protoc 10(6):845-58. Morris et al. 2009 J. Computational Chemistry 2009, 16: 2785-91.) The ligands that exhibited the best binding capacities are presented in  FIG. 14 , including phosphonate inhibitor ( FIG. 14A-D ), trehalose ( FIG. 14  E-H), and cyclipostins and cyclophostin (CyC) ( FIG. 14  I-K). The binding capacity between the ligand and target was scored by their binding energy, where the lower the binding energy, the more favorable the binding. The binding capacity of phosphonate inhibitor analogs, specifically phosphonate inhibitor 6a, is most favorable, while CyC analogs also exhibited effective binding. 
     It is now shown that the phosphonate inhibitor and their analogs that favorably bind to tmytC. The knowledge of ligand-target binding is at the basis of rational drug design. Computer technology is valuable in the drug discovery process as it allows virtual screening of compounds in silico for their binding capacity which aid the compilation of a subset of best binding compounds which can be confirmed by further testing. It also allows novel compounds to be designed and optimized. Our results have provided candidate tmytC inhibitors molecules that can bind to TtmytC. 
     6.2 Discussion 
     We documented that  Tsukamurella  is an ocular pathogen by fulfilling the Koch&#39;s postulates using the NZW rabbit keratitis model. Although cases of ocular infections due to  Tsukamurella  have been increasingly identified in recent years 3,5,6,9-11 , this group of bacteria has been relatively understudied. Our recent study based on the analysis of the largest number of  Tsukamurella  cases reported so far showed that they played a significant but previously underestimated role in ocular infections 11 . Thus, the availability of an animal model to confirm the causal relationship between  Tsukamurella  and ocular infections and to study its treatment strategies and pathogenesis mechanisms is of paramount importance. Similar to animal studies of other important ocular pathogens, such as  S. aureus  and  P. aeruginosa   23 , we demonstrated that the NZW rabbit is an excellent model for  Tsukamurella  keratitis.  T. pulmonis -PW 1004 was recovered in abundance and in pure culture from all rabbits infected with  Tsukamurella , but the bacteria were not recovered in the control group ( FIG. 1B ). The rabbits with keratitis produced clinical features similar to those observed in patients with ocular infections ( FIG. 1A ). Histological examination further revealed marked pathological damage in corneal tissues of  Tsukamurella  inoculated rabbits but not in control rabbits ( FIGS. 1C, 3B, 5B ). When isolates of  T. pulmonis  recovered from rabbits were used to infect another group of healthy rabbits, it caused keratitis with the same clinical, pathological and histopathological characteristics, fulfilling the Koch&#39;s postulate. This animal model was used for downstream treatment and pathogenesis studies. 
     None of the 4 multi-purpose contact lens solutions with their original compositions were able to achieve the minimal antimicrobial efficacy against  Tsukamurella  according to ISO14729 regulations, but when PHMB was increased to a final concentration of 0.0025%, all these 4 contact lens solutions tested were able to meet the ISO14729 standard. Contact lens wear is a well-recognized risk factor of bacterial keratitis. In the present study, we found that all the 4 commonly used contact lens solutions tested exhibited poor efficacy in killing  Tsukamurella  ( FIG. 2A ). The original compositions of these 4 solutions contained 1 to 2 common antimicrobial agents used in contact lens solutions, including PHMB, polyquaternium and/or myristamidopropyl dimethylamine (Table 1). Among these antimicrobial agents, PHMB (0.0001-0.00013%) was present in 3 of the 4 solutions tested. PHMB is a polymeric biguanide with broad spectrum activities against both Gram-positive and Gram-negative bacteria. It has been widely used as an antimicrobial ingredient in contact lens solutions and environmental biocides 24,25 . Results showed that when the final concentration of PHMB was increased to 0.0025% in the contact lens solutions, their efficacies in killing  Tsukamurella  could meet the ISO standard ( FIG. 2C ). 
     PHMB is also a potential drug of choice for the treatment of  Tsukamurella  keratitis.  Tsukamurella  are generally resistant to commonly used topical antibiotics eye drops, such as tetracycline and chloramphenicol, but they are susceptible to levofloxacin 3,12 . Therefore, the therapeutic option for  Tsukamurella -associated ocular infections is rather limited. Notably, despite the wide usage of PHMB, acquired resistance to PHMB has not been reported so far. Therefore, we studied the efficacy of PHMB and levofloxacin against  Tsukamurella  using our rabbit keratitis model. Corneal perforations with mild to severe discharges were observed in rabbits treated with levofloxacin, and the experiment of this treatment group was terminated. This observation was in line with a previous study which reported an increased incidence of corneal perforation in patients after topical fluoroquinolone treatment 26 . Subsequent studies in animals also showed that topical levofloxacin could induce expression of matrix metalloproteinases in the cornea which may predispose patients to corneal perforation 27,28 . In contrast, corneal perforation was not observed in rabbits treated with PHMB, and there were marked improvement in clinical signs and histological features and significant reductions in  Tsukamurella  counts from rabbit corneas of this treatment group compared to those treated with normal saline ( FIG. 3A , B, C). It was observed that the concentration of PHMB (0.02%) used in the present study caused no toxicity in rabbit corneal tissues. Given these promising results, the next phase of clinical trial is currently ongoing to investigate the efficacy, safety, and tolerability of 0.08% of PHMB for the treatment of  Acanthamoeba keratitis   31 . Further studies can be carried out to determine the optimal concentration of PHMB in the treatment of  Tsukamurella  keratitis. 
     TmytC is a virulence factor of  Tsukamurella  as demonstrated using in vivo rabbit keratitis model. This is also the first report demonstrated the novel role of TmytC in causing ocular infections. In this study, genome sequencing and annotation of the two ocular isolates,  T. pulmonis -PW 1004 and  T. tyrosinosolvens -PW899, revealed a number of genes that may be involved in pathogenesis (Table 4). Among these genes, both genomes contained 3 homologs of genes (tmytA, tmytB, and tmytC) encoding mycolyltransferase ( FIG. 4 ). This enzyme functions by transferring one mycolate residue from trehalose monomycolate (TMM) to another molecule of TMM yielding trehalose 6,6′-dimycolate, which will then be processed by esterase to form free mycolic acids 20 . Our results clearly showed marked attenuated virulence and survival after knocking out of tmytC in  T. pulmonis -PW 1004 ( FIGS. 5A , B, C). Taken together, the present results supported that TmytC is an important virulence factor for  Tsukamurella  keratitis. Specific inhibitors targeting TmytC, alone or in combination with other antibiotics such as PHMB, could serve as an armamentarium for the treatment of  Tsukamurella  infections. 
     6.3 Tables 
       
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Contact lens solutions tested in the present study 
               
            
           
           
               
               
               
            
               
                   
                   
                 Manufacturer&#39;s 
               
               
                 Commercial  
                   
                 recommended 
               
               
                 name (Manufacturer) 
                 Active ingredients for disinfection 
                 disinfection time 
               
               
                   
               
               
                 Biotrue Multi-Purpose Solution 
                 PHMB 0.00013%, polyquaternium 
                 4 h 
               
               
                 (Bausch + Lomb, USA) 
                 0.0001% 
                   
               
               
                 RENU Multi-Purpose Solution 
                 PHMB 0.0001% 
                 4 h 
               
               
                 (Bausch + Lomb, USA) 
                   
                   
               
               
                 COMPLETE Multi-Purpose 
                 PHMB 0.0001% 
                 6 h 
               
               
                 Solution (Abott, USA) 
                   
                   
               
               
                 OPTI-FREE RepleniSH (Alcon, 
                 POLYQUAD ® (polyquaternium) 
                 6 h 
               
               
                 USA) 
                 0.001% and ALDOX 
                   
               
               
                   
                 (myristamidopropyl dimethylamine) 
                   
               
               
                   
                 0.0005% 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Susceptibility of  T. pulmonis - 
               
               
                 PW1004 to a series of PHMB concentrations 
               
            
           
           
               
               
               
            
               
                   
                 PHMB concentration (%) 
                 Zone of inhibition (mm) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 0 
                 0 
               
               
                   
                 0.0005 
                 0 
               
               
                   
                 0.001 
                 0 
               
               
                   
                 0.0025 
                 13 
               
               
                   
                 0.005 
                 14 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Results of draft genome assembly of  T. tyrosinosolvens - 
               
               
                 PW899 and  T. pulmonis -PW1004 
               
            
           
           
               
               
               
            
               
                   
                   T. tyrosinosolvens - 
                   T. pulmonis - 
               
               
                 Genome assembly data 
                 PW899 
                 PW1004 
               
               
                   
               
               
                 Genome size 
                 4.88 Mb 
                 4.60 Mb 
               
               
                 G + C content 
                 71.0% 
                 70.9% 
               
               
                 Total no. of contigs 
                 321 
                 266 
               
               
                 No. of contigs (&gt;500 bp) 
                 307 
                 245 
               
               
                 No. of predicted protein- 
                 4,558 
                 4,241 
               
               
                 coding genes 
                   
                   
               
               
                 No. of subsystems 
                 399 
                 384 
               
               
                 No. of tRNAs 
                 49 
                 47 
               
               
                 No. of rRNA operons 
                 3 
                 3 
               
               
                 GenBank accession no. 
                 QPKD00000000 
                 QQQF00000000 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Putative genes related to pathogenesis in  T.   tyrosinosolvens -PW899 and  
               
               
                   T.   pulmonis -PW1004 respectively 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 Bacteria with 
                 Amino 
                   
                   
               
               
                 GenBank 
                   
                   
                 the closest 
                 acid 
                   
                   
               
               
                 accession 
                   
                   
                 matching 
                 identities 
                   
                   
               
               
                 number of 
                   
                   
                 sequences to 
                 to 
                   
                   
               
               
                 PW899 
                   
                   
                 PW899 
                 PW899 
                 Pathways 
                   
               
               
                 (PW1004) 
                 Gene 
                 Protein 
                 (PW1004) 
                 (PW1004) 
                 involved 
                 References 
               
               
                   
               
               
                 RDB46325.1 
                 tmytA 
                 Mycolyltransferase 
                 
                   W. limnetica  
                 
                 45% 
                 Cell wall 
                 Ojha et 
               
               
                 (RDH10422.1) 
                   
                   
                 ( W.   
                 (45%) 
                 synthesis 
                 al. 19   
               
               
                   
                   
                   
                   limnetica ) 
                   
                   
                   
               
               
                 RDB46324.1 
                 tmytB 
                 Mycolyltransferase 
                 
                   W. limnetica  
                 
                 44% 
                 Cell wall 
                 Ojha et al. 19   
               
               
                 (RDH10421.1) 
                   
                   
                 ( W.   
                 (44%) 
                 synthesis 
                   
               
               
                   
                   
                   
                   limnetica ) 
                   
                   
                   
               
               
                 RDB46325.1 
                 tmytC 
                 Mycolyltransferase 
                 
                   W. limnetica  
                 
                 45% 
                 Cell wall 
                 Ojha et al. 19   
               
               
                 (RDH10422.1) 
                   
                   
                 ( W.   
                 (45%) 
                 synthesis 
                   
               
               
                   
                   
                   
                   limnetica ) 
                   
                   
                   
               
               
                 RDB46803.1 
                 smeg1529 
                 Serine esterase 
                 
                   Mycolicibacterium 
                 
                 44% 
                 Cell wall 
                 Ojha et al. 19   
               
               
                 (RDH10071.1) 
                   
                   
                 
                   aromaticivorans 
                 
                 (42%) 
                 synthesis 
                   
               
               
                   
                   
                   
                 ( M . 
                   
                   
                   
               
               
                   
                   
                   
                   aromaticivorans ) 
                   
                   
                   
               
               
                 RDB46314.1 
                 pks16 
                 Putative 
                 
                   Gordonia 
                 
                 73% 
                 Lipid 
                 Ojha et al. 18   
               
               
                 (RDH10413.1) 
                   
                 polyketide 
                 
                   kroppenstedtii 
                 
                 (72%) 
                 synthesis 
                   
               
               
                   
                   
                 synthase 
                 ( G . 
                   
                   
                   
               
               
                   
                   
                   
                   kroppenstedtii ) 
                   
                   
                   
               
               
                 RDB47756.1 
                 fadD26 
                 Fatty-acid- 
                 
                   Gordonia 
                 
                 75% 
                 Lipid 
                 Mohandas 
               
               
                 (RDH09883.1) 
                   
                 CoA ligase 
                 
                   aichiensis 
                 
                 (73%) 
                 synthesis 
                 et al. 45   
               
               
                   
                   
                   
                 ( G . 
                   
                   
                   
               
               
                   
                   
                   
                   aichiensis ) 
                   
                   
                   
               
               
                 RDB45407.1 
                 papA5 
                 Phthiocerol/ 
                 
                   Gordonia 
                 
                 69% 
                 Lipid 
                 Mohandas 
               
               
                 (RDH12857.1) 
                   
                 phthiodiolone 
                   effuse  ( G . 
                 (62%) 
                 synthesis 
                 et al. 45   
               
               
                   
                   
                 dimycocerosyl 
                   polyisoprenivorans ) 
                   
                   
                   
               
               
                   
                   
                 transferase 
                   
                   
                   
                   
               
               
                 RDB49989.1 
                 mmpL11 
                 Mycobacterial 
                 
                   Gordonia 
                 
                 73% 
                 Lipid 
                 Wright et 
               
               
                 (RDH13721.1 
                   
                 membrane 
                 
                   desulfuricans 
                 
                 (73%) 
                 synthesis 
                 al. 46   
               
               
                   
                   
                 protein large 
                 ( G . 
                   
                   
                   
               
               
                   
                   
                   
                   desulfuricans ) 
                   
                   
                   
               
               
                 RDB47405.1 
                 groEL1 
                 Heat shock 
                 
                   Rhodococcus 
                 
                 75% 
                 Mycolic 
                 Ojha et al. 47   
               
               
                 (RDH10177.1) 
                   
                 protein 1 
                 
                   rhodochrous 
                 
                 (75%) 
                 acid 
                   
               
               
                   
                   
                   
                 ( R . 
                   
                 synthesis 
                   
               
               
                   
                   
                   
                 r hodochrous ) 
                   
                   
                   
               
               
                 RDB48772.1 
                 mmaa4 
                 Methoxy 
                 
                   Mycobacterium  
                 
                 64% 
                 Mycolic 
                 Sambandan 
               
               
                 (RDH09310.1) 
                   
                 mycolic acid 
                 
                   avium 
                 
                 (70%) 
                 acid 
                 et al. 48   
               
               
                   
                   
                 synthase 
                 complex 
                   
                 synthesis 
                   
               
               
                   
                   
                   
                 ( Rhodococcus    
                   
                   
                   
               
               
                   
                   
                   
                   zopfii ) 
                   
                   
                   
               
               
                 RDB45065.1 
                 lsr2 
                 Leprosy serum 
                 
                   Mycobacteroides 
                 
                 64% 
                 Mycolic 
                 Chen et al. 49   
               
               
                 (RDH10897.1) 
                   
                 reactive clone 
                 
                   abscessus 
                 
                 (67%) 
                 acid 
                   
               
               
                   
                   
                 2 
                 ( M . 
                   
                 synthesis 
                   
               
               
                   
                   
                   
                   abscessus ) 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Bacterial strains and plasmids used in this study 
               
            
           
           
               
               
               
            
               
                 Strains or  
                   
                 Source or 
               
               
                 plasmids 
                 Genotype and descriptions 
                 reference 
               
               
                   
               
               
                 Strains 
                   
                 Invitrogen 
               
               
                   E. coli  DH5α 
                 F-φ80lacZΔM15 Δ(lacZYA-argF) U169 
                 Invitrogen 
               
               
                   
                 recA1 endA1 hsdR17 (rk−, mk+) gal- 
                   
               
               
                   
                 phoA supE44 λ-thi-1 gyrA96 relA1 
                   
               
               
                 
                   T. tyrosinosolvens 
                 
                 Corneal scraping of a patient with  
                 Woo et al. 5   
               
               
                 PW899 
                 keratitis 
                   
               
               
                 
                   T. tyrosinosolvens 
                 
                 Eye swab of a patient with  
                 Woo et al. 6   
               
               
                 PW1006 
                 conjunctivitis 
                   
               
               
                 
                   T. tyrosinosolvens 
                 
                 Eye swab of a patient with  
                 Teng et al. 11   
               
               
                 PW3869 
                 conjunctivitis 
                   
               
               
                 
                   T. tyrosinosolvens 
                 
                 Corneal scraping of a patient with  
                 Teng et al. 11   
               
               
                 PW3874 
                 corneal ulcer 
                   
               
               
                 
                   T. tyrosinosolvens 
                 
                 Corneal scraping of a patient with  
                 Teng et al. 11   
               
               
                 PW3876 
                 corneal ulcer 
                   
               
               
                 
                   T. tyrosinosolvens 
                 
                 Eye swab of a patient with  
                 Teng et al. 11   
               
               
                 PW4092 
                 conjunctivitis 
                   
               
               
                 
                   T. pulmonis 
                 
                 Eye swab of a patient with  
                 Woo et al. 6   
               
               
                 PW1004 
                 conjunctivitis 
                   
               
               
                 
                   T. pulmonis 
                 
                 Corneal scraping of a patient with  
                 Teng et al. 11   
               
               
                 PW3877 
                 corneal infiltrate 
                   
               
               
                 
                   T. pulmonis 
                 
                 Conjunctival scraping of a patient with 
                 Teng et al. 11   
               
               
                 PW3882 
                 conjunctivitis 
                   
               
               
                 
                   T. hongkongensis 
                 
                 Corneal scraping of a patient with  
                 Teng et  
               
               
                 HKU52 T   
                 keratitis 
                 al. 9, 11   
               
               
                 
                   T. sinensis 
                 
                 Conjunctival swab of a patient with 
                 Teng et al. 9   
               
               
                 HKU51 T   
                 conjunctivitis 
                   
               
               
                 
                   T. sinensis 
                 
                 Right eye swab of a patient with  
                 Teng et al. 11   
               
               
                 PW3895 
                 eye redness 
                   
               
               
                 
                   T. ocularis 
                 
                 Eye swab of a patient with conjunctivitis 
                 Teng et al. 10   
               
               
                 HKU63 T   
                   
                   
               
               
                 
                   T. ocularis 
                 
                 Eye swab of a patient with conjunctivitis 
                 Teng et al. 10   
               
               
                 HKU64 
                   
                   
               
               
                 
                   T. hominis 
                 
                 Eye swab of a patient with conjunctivitis 
                 Teng et al. 10   
               
               
                 HKU65 T   
                   
                   
               
               
                   T. spumae  JCM 
                 Foam of a activated sludge plant 
                 Nam et al. 50   
               
               
                 12608 T   
                   
                   
               
               
                 
                   P. aeruginosa 
                 
                 Blood specimen from a patient 
                 ATCC 
               
               
                 ATCC27853 
                   
                   
               
               
                 PW1004 
                 PW1004 derivative with galK  
                 Present  
               
               
                   
                 deletion, ΔgalK  
                 study 
               
               
                 PW1004ΔtmytA 
                 PW1004 derivative with tmytA  
                 Present  
               
               
                   
                 deletion, ΔgalK 
                 study 
               
               
                 PW1004ΔtmytB 
                 PW1004 derivative with tmytB  
                 Present  
               
               
                   
                 deletion, ΔgalK 
                 study 
               
               
                 PW1004ΔtmytC 
                 PW1004 derivative with tmytC  
                 Present  
               
               
                   
                 deletion, ΔgalK 
                 study 
               
               
                 Plasmids 
                   
                   
               
               
                 pCR ®-XL- 
                 Cloning vector, pUC ori kan 
                 Invitrogen 
               
               
                 TOPO ® 
                   
                   
               
               
                 p2NIL 
                 Suicidal plasmid, oriE kan 
                 Parish et al. 51   
               
               
                 pNV18 
                   Tsukamurella / E. coli  shuttle vector, aph 
                 Chiba et al. 44   
               
               
                 p2NIL-GalK 
                 p2NIL expressing wild-type GalK under  
                 Present  
               
               
                   
                 the control of the hsp60 promoter, kan 
                 study 
               
               
                 pCR-XL-tmytA 
                 pCR-XL containing tmytA and flanking 
                 Present  
               
               
                   
                 fragments, kan 
                 study 
               
               
                 pCR-XL-tmytB 
                 pCR-XL containing tmytB and flanking 
                 Present  
               
               
                   
                 fragments, kan 
                 study 
               
               
                 pCR-XL-tmytC 
                 pCR-XL containing tmytC and flanking 
                 Present  
               
               
                   
                 fragments, kan 
                 study 
               
               
                 pΔtmytA 
                 p2NIL containing flanking fragments  
                 Present  
               
               
                   
                 of tmytA, expressing GalK under the  
                 study 
               
               
                   
                 control of the hsp60 promoter, kan 
                   
               
               
                 pΔtmytB 
                 p2NIL containing flanking fragments  
                 Present  
               
               
                   
                 of tmytB, expressing GalK under the  
                 study 
               
               
                   
                 control of the hsp60 promoter, kan 
                   
               
               
                 pΔtmytC 
                 p2NIL containing flanking fragments  
                 Present  
               
               
                   
                 of tmytC, expressing GalK under the  
                 study 
               
               
                   
                 control of the hsp60 promoter, kan 
                   
               
               
                 ptmytC 
                 pNV18 expressing ORF of tmytC  
                 Present  
               
               
                   
                 under the control of the hsp60  
                 study 
               
               
                   
                 promoter, aph, for TmytC protein  
                   
               
               
                   
                 expression 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Primers used in this study 
               
            
           
           
               
               
               
            
               
                   
                   
                 Restriction 
               
               
                 Primers 
                 Sequence (5′ to 3′) a   
                 site 
               
               
                   
               
            
           
           
               
            
               
                 Primers for mutagenesis of tmytA 
               
            
           
           
               
               
               
            
               
                 tmytA-UF-1 
                 GTGCCCGGCGCCGCTGA 
                   
               
               
                   
               
               
                 tmytA-DR-1 
                 TGATCTGCGCGACCGACCGGT 
                   
               
               
                   
               
               
                 tmytA-UF 
                   CCCAAGCTT GTGCCCGGCGCCGCTGA 
                 HindIII 
               
               
                   
               
               
                 tmytA-UR 
                   CCCAAGCTT CATGGGAACAGTGTTACACGGGTGT 
                 HindIII 
               
               
                   
               
               
                 tmytA-DF 
                   CGCGGATCC GACGACCGGCCGGGGGTT 
                 BamHI 
               
               
                   
               
               
                 tmytA-DR 
                   CGCGGATCC TGATCTGCGCGACCGACCGGT 
                 BamHI 
               
               
                   
               
               
                 Inner-tmytA-F 
                 GCGAGCGCGAGCCCGTG 
                   
               
               
                   
               
               
                 Inner-tmytA-R 
                 GTGGCCGGCAGCGACGT 
                   
               
               
                   
               
            
           
           
               
            
               
                 Primers for mutagenesis of tmytB 
               
            
           
           
               
               
               
            
               
                 tmytB-UF-1 
                 GGCGGCGATGGTGCGAAGAGA 
                   
               
               
                   
               
               
                 tmytB-DR-1 
                 TGTGGGTGCCCACCGACGAGAAGT 
                   
               
               
                   
               
               
                 tmytB-UF 
                   CCCAAGCTT GGCGGCGATGGTGCGAAGAGA 
                 HindIII 
               
               
                   
               
               
                 tmytB-UR 
                   CCCAAGCTT TCTTGGCCCAGCCGTTGCGCAT 
                 HindIII 
               
               
                   
               
               
                 tmytB-DF 
                   CGCGGATCCT GGGGCTACTGGCAGGATCA 
                 BamHI 
               
               
                   
               
               
                 tmytB-DR 
                   CGCGGATCC GGTGCCCACCGACGAGAAGT 
                 BamHI 
               
               
                   
               
               
                 Inner-tmytB-F 
                 ATTCGGACGGAAAAGCACCTGCTGTA 
                   
               
               
                   
               
               
                 Inner-tmytB-R 
                 AGCCTTGTCACAGCCGTCACTCT 
                   
               
               
                   
               
            
           
           
               
            
               
                 Primers for mutagenesis of tmytC 
               
            
           
           
               
               
               
            
               
                 tmytC-UF-1 
                 GTCTGCGCGCCACCTGGGA 
                   
               
               
                   
               
               
                 tmytC-DR-1 
                 GCAGGCCCTTGGATCCGACGGT 
                   
               
               
                   
               
               
                 tmytC-UF 
                   CCCAAGCTT GTCTCGCTGGTCGGCCTGTCG 
                 HindIII 
               
               
                   
               
               
                 tmytC-UR 
                 GGTCGCTCCCCCAGGCTGCTCGCATTGCT 
                   
               
               
                   
               
               
                 tmytC-DF 
                 GCAGCCTGGGGGAGCGACCAGGTCTGGCAGATG 
                   
               
               
                   
               
               
                 tmytC-DR 
                   CCCAAGCTT CAGGCCCTTGGATCCGACGGT 
                 HindIII 
               
               
                   
               
               
                 Inner-tmytC-F 
                 AGGAAACCGGGAGTGTCTGTAACGC 
                   
               
               
                   
               
               
                 Inner-tmytC-R 
                 AGGGGCTCGTCGACGTCGGT 
                   
               
               
                   
               
            
           
           
               
            
               
                 Primers for expression of tmytC 
               
            
           
           
               
               
               
            
               
                 hsp60-F 
                   CCAAGCTT ACGCTCGACTCCAATACGGGGGTT 
                 HindlII 
               
               
                   
               
               
                 hsp60-R 
                 GGCTGCTCGCATTCGATACCTCCTTTTGCGAAGT 
                   
               
               
                   
                 GATTCCT 
                   
               
               
                   
               
               
                 tmytC-F 
                 GGAGGTATCGAATGCGAGCAGCCTGGGGTAAGC 
                   
               
               
                   
               
               
                 tmytC-R 
                   CTAGTCTAGA TCAGCTGTTGAACCAGCCGGTG 
                 XbaI 
               
               
                   
               
               
                   a Restriction sites in the primer sequences are in underlined. 
               
            
           
         
       
     
     6.4 Methods 
     6.4.1 Bacterial strains and growth conditions. The source of all  Tsukamurella  strains used in this study is detailed in Table 5. Of note,  T. pulmonis -PW1004 was previously isolated from the serous discharge of a 69-year-old Chinese woman with conjunctivitis, while  T. tyrosinosolvens -PW899 was previously isolated from the corneal scraping of an 87-year-old Chinese woman with keratitis (Table 5) 5,6 . Unless otherwise specified, frozen stock of all  Tsukamurella  isolates were grown on brain heart infusion (BHI) agar at 37° C. under aerobic conditions for 48 h. Isolated colonies were cultured in BHI at 37° C. After 2 days of incubation, the broth culture was subcultured in BHI and grown to 10 8  CFU/ml. Growth phase and bacterial cell density were determined spectrophotometrically by measuring the optical density at 600 nm (OD 600 ). 
     To examine the growth kinetics of the PW1004-WT, tmytC knockout and complemented mutants, overnight bacterial cultures were diluted 1:50 into BHI broth and further cultured under aerobic conditions at 37° C. One milliliter of cell suspension was monitored at different time points by measuring the OD 600 . Experiments were performed in triplicate and repeated 3 times. 
     6.4.2 Contact lens solutions. Four commercially available contact lens solutions, including Biotrue multi-purpose solution (Bausch+Lomb, USA), RENU multi-purpose solution (Bausch+Lomb, USA), COMPLETE multi-purpose solution (Abbott, USA), and OPTI-FREE RepleniSH (Alcon, USA), were evaluated in this study. To minimize lot-to-lot variation, 3 lots from each solution were pooled and tested. Details of ingredients and recommended disinfection time of each contact lens solution are listed in Table 1. 
     6.4.3 Draft genome sequencing and analysis. The draft genomes of the 2  Tsukamurella  species,  T. tyrosinosolvens -PW899 and  T. pulmonis -PW1004, were determined by high-throughput sequencing. Genomic DNA was extracted from overnight cultures of each  Tsukamurella  strain grown on BHI agar by QIAGEN Genomic-tip 20/G kit according to the manufacturer&#39;s instructions (QIAGEN). Each DNA sample was sequenced by 151-bp Illumina Hi-Seq 1,500 paired-end reads with a mean library size of 350 bp. Sequencing errors were corrected by k-mer frequency spectrum analysis using SOAPec v2.0.1 32 . De novo assembly was performed using Velvet 1.2.10 33 . Prediction of protein coding regions and automatic functional annotation was performed using RAST (Rapid Annotations using Subsystem Technology) server version 2.0 34  and COGs 35 . Graphical circular maps of both genomes were performed with CGview 36 . This Whole Genome Shotgun project has been deposited in DDBJ/EMBL/GenBank under the accession numbers QPKD00000000; BioSample SAMN09691326 for  T. tyrosinosolvens -PW899 and QQQF00000000; BioSample SAMN09691327 for  T. pulmonis -PW1004. 
     6.4.4 Development of a rabbit model for  Tsukamurella  keratitis. Bacterial suspensions used to infect rabbits were prepared by culturing  T. pulmonis -PW1004 in BHI for 48 h. Eight male NZW rabbits, 1.5-2.0 kg, were inoculated intrastromally as described previously 37 . Corneas of 4 rabbits were injected with approximately 10 μl (i.e., 10 6  CFU) of  T. pulmonis -PW1004 using a microliter syringe with a 30G needle. Another 4 rabbit corneas were challenged with plain culture medium as the control. Rabbits were monitored daily for signs of disease. At 24 h PI, rabbit eyes were photographed, evaluated for pathology, and sacrificed. After euthanasia, the corneas of each rabbit were surgically removed for histopathological and immunohistochemical analyses and bacterial enumeration. 
     6.4.5 Treatment of experimental  Tsukamurella  keratitis. Efficacy of the two antibiotics, topical 0.5% Cravit® levofloxacin (Santen Pharmaceutical Company, Japan) and 0.02% PHMB (Lonza, Switzerland), for the treatment of  Tsukamurella  keratitis were evaluated, respectively.  Tsukamurella  keratitis was first established in 12 NZW rabbits (n=4 per group) using procedures as described above. Infection was allowed to proceed for 24 h before initiation of antibiotic therapy. These 12 NZW rabbits were divided into 3 topical treatment groups: (1) 0.5% levofloxacin, (2) 0.02% PHMB, and (3) saline. Treatment regimens of levofloxacin and PHMB were performed according to Fiscella et al. and Kowalski et al., respectively, with slight modifications 16,17 . For the first group of rabbits treated with levofloxacin (n=4), drops (50 μl) of levofloxacin were applied to the affected eyes hourly for 10 doses over 3 days. For the second group of rabbits treated with PHMB (n=4), drops (50 μl) of PHMB were applied to the affected eyes hourly for 8 doses over 3 days. Rabbits in the third control group (n=4) received the same regimen of sterile saline (0.85% NaCl) hourly for 10 doses over 3 days. In addition to these 3 treatment groups, two extra NZW rabbits without infection were used as controls (i.e., mock-infected and mock-treated rabbits), receiving the same regimen of saline for 3 days. One hour after the final instillation of the antibiotics and saline drops, rabbit eyes were photographed, evaluated for pathology, and sacrificed. The treatment efficacy was compared and evaluated by the quantitative culture and histopathological analysis of the infected corneas. 
     6.4.6 Quantification of  Tsukamurella  cells. To quantify the number of viable  Tsukamurella  in the cornea, the cornea harvested from each rabbit was cut into smaller pieces using a sterile scalpel. The corneal pieces were placed into a sterile tube containing 500 μl of PBS (pH 7.2). Each tissue was homogenized, and homogenates were serially diluted 10-fold in PBS (pH 7.2). One hundred microliters of each diluted sample was plated in triplicate on the BHI agar and incubated at 37° C. under aerobic conditions for 48 h. The number of bacteria was determined and expressed as CFU/cornea. 
     6.4.7 Histopathological and immunohistochemical analyses. To perform immunohistochemical staining on infected rabbit tissues, mice antiserum against  T. pulmonis -PW1004 was produced by subcutaneously injecting 200 μl of heat-inactivated  Tsukamurella  cells (i.e., 10 7  CFU) into 3 mice, using an equal volume of complete Freund&#39;s adjuvant (Sigma, USA) as described previously 38 . Incomplete Freund&#39;s adjuvant (Sigma, USA) was used in subsequent immunizations. Three inoculations per mouse were administered once every 2 weeks. Two weeks after the last immunization, 100 μl of blood was collected via the lateral saphenous vein of the mice to obtain the sera. Serum samples collected from a mock-infected mouse was used as the control antibody. 
     To examine the histopathology of corneal tissues of rabbits challenged with the PW1004-WT and its derivative mutants, excised infected eyes, including the cornea of challenged rabbits, were subjected to histopathological examination. Corneal tissues harvested from the rabbits were fixed in 10% neutral-buffered formalin, embedded in paraffin, and stained with hematoxylin and eosin (H&amp;E) according to Fischer et al. 39 . Histopathological changes among different groups of rabbits were observed using an Olympus BX53 Digital Upright Microscope with DP80 microscope camera (Tokyo, Japan) and imaging system. Infected tissues from challenged rabbits were subject to immunohistochemical staining for  Tsukamurella  as described previously 38 . Tissue sections were deparaffinized and rehydrated, followed by blocking endogenous peroxidase with 0.3% H 2 O 2  for 30 min, and then with 1% bovine serum albumin/PBS at room temperature for 30 min to minimize non-specific staining. The tissue sections were then pre-treated with streptavidin solution and biotin solution at room temperature for 15 min, respectively, to avoid high background signals due to the endogenous biotin or biotin-binding proteins in the tissues. The sections were incubated at 4° C. overnight with 1:4,000 dilution of mouse anti- T. pulmonis -PW1004 serum or pre-immune serum, followed by incubation of 30 min at room temperature with 1:500 dilution of biotin-conjugated goat anti-mouse immunoglobulin G (IgG), H&amp;L chain (Abcam). Streptavidin/peroxidase complex reagent (Vector Laboratories) was then added and incubated at room temperature for 30 min. Sections were counterstained with hematoxylin. Tissues from sterile saline controls were included as negative controls. Color development was performed using 3,3′-diaminobenzidineand images captured with Nikon 80i imaging system and spot-advance computer software. 
     6.4.8 MPO assay. MPO is a marker enzyme for measuring PMN accumulation in tissue samples. Therefore, the number of infiltrating PMNs into the corneas of rabbits can be quantitated by measuring the amount of MPO activity in corneal homogenates. The assay involves a colorimetric reagent, o-dianisidine, which can react with the hypochlorite produced by the MPO reaction. Briefly, 20 n1 of tissue homogenate was mixed with 180 n1 of 50 mM potassium phosphate buffer (pH 6.0) containing 16.7 mg/ml o-dianisidine dihydrochloride and 0.0005% hydrogen peroxide. The change in optical density at 460 nm was measured continuously for 10 min at room temperature with a microplate reader. One MPO unit of activity is equivalent to approximately 100,000 PMNs 41 . All experiments were performed in triplicate and repeated 3 times. 
     6.4.9 In vitro susceptibility of planktonic cultures of  Tsukamurella  against contact lens and PHMB solutions. A susceptibility test was performed following the procedures as described in FDA/ISO14729 stand-alone procedure for disinfecting products 13 . Briefly, 0.1 ml of 1×10 8  CFUs/ml bacterial suspension from 7 different  Tsukamurella  species was added into 10 ml each of the 4 commercial contact lens solutions, respectively, and the mixture was incubated at room temperature according to the manufacturer&#39;s recommended disinfection time (Table 1). After incubation, a 1-ml aliquot was withdrawn from each mixture and added to 9 ml of Dey-Engley neutralizing broth (Sigma, USA) for 15 min at room temperature for neutralization of the preservative. The mixture was then serially diluted, and 100 n1 of each diluted sample was plated in triplicate on the BHI agar for sampling of viable bacteria.  P. aeruginosa  ATCC27853 was used as a control. The mean logarithmic reduction was calculated. According to the guideline, only a contact lens solution capable of reducing the viability of starting concentration of bacteria by 3-log is defined as satisfactory. All experiments were performed in triplicate and repeated 3 times along with the control strain. 
     Disk diffusion assay was initially used to determine the susceptibility of  T. pulmonis -PW1004 against various concentrations of PHMB. Briefly, standard paper disks, 6 mm in diameter, impregnated with different dilutions of PHMB (0.0005%, 0.001%, 0.0025%, 0.005%) were placed onto BHI agar plates inoculated with overnight culture of a 0.5 McFarland standard prepared from  T. pulmonis -PW1004, following standard procedures 15  Paper disks soaked in 0.85% NaCl were used as the control. Zones of inhibition were measured after 48 h of incubation at 37° C. under aerobic conditions. Preliminary results showed that the 0.0025% of PHMB was the minimal concentration that achieved good efficacy against  T. pulmonis -PW1004. Next, we re-examined the susceptibility of the 4 contact lens solutions against the 7  Tsukamurella  species by adjusting the final concentration of PHMB to 0.0025%, following the procedures as described in the previous paragraph. 
     6.4.10 Construction of non-polar deletion mutant strains. Bacterial strains and plasmids used in this part of the study are listed in Table 5. The wild-type  T. pulmonis -PW1004 was a clinical strain isolated from a patient in Hong Kong 6 . Unmarked, non-polar deletion of tmytA, tmytB, and tmytC were constructed respectively by homologous recombination using our newly developed suicide plasmid p2NIL-GalK (Table 5). Primers used for deletion mutagenesis are listed in Table 6. Suicide plasmid p2NIL-GalK and parent strain  T. pulmonis -PW1004 were used for constructing in-frame deletion mutants by homologous recombination 42 . Primers tmytC-UF-1/DR-1 were used to amplify the wild-type tmytC gene (966 bp) and its upstream (1,031 bp) and downstream (733 bp) regions from genomic DNA of  T. pulmonis -PW1004. Polymerase chain reaction (PCR) product was purified using QIAquick PCR purification kit (QIAGEN, USA) and cloned to pCR®-XL-TOPO® (Invitrogen, USA) to generate pCR-XL-tmytC. 5′- and 3′-flanking regions of tmyC gene were amplified by PCR from plasmid DNA of pCR-XL-tmytC, using primers tmytC-UF-HindIII/UR and tmytC-DF/DR-HindIII, respectively, and the individual PCR products were mixed to generate an in-frame deletion pattern of the tmytC gene by an overlapping PCR method. The overlapping amplicon containing the in-frame deletion pattern was cloned into p2NIL-GalK, resulting in the final construct of pΔtmytC, which was electro-transformed into  Escherichia coli  DH5α 43 . Transformants were first selected on BHI agar with 100 μg/ml kanamycin. After that, colonies with single recombination were further cultured on BHI agar (without antibiotics) and selected on BHI agar with 0.5% 2-deoxy-D-galactose (without antibiotics) to obtain the final double recombinants 42 . All 2-deoxy-D-galactose-resistant colonies were checked for kanamycin sensitivity and screened by primers tmytC-UF-1/DR-1. All mutants were confirmed by DNA sequencing using inner-tmytC-F/R primers. 
     6.4.11 Complementation of PW1004ΔtmytC. The coding region of tmytC gene, together with its ribosome-binding site, was amplified from chromosomal DNA of PW1004 using primer hsp60-F/R and tmytC-F/R and subcloned into expression shuttle vector pNV18 44 , resulting in the final construct pNV18-tMytC. The complementation plasmid was transformed into PW1004ΔtmytC, and TmytC protein was constitutively expressed. A mutant strain transformed with empty plasmid pNV18 was used as a negative control. 
     6.4.12 Statistical Analysis. Unless stated otherwise, data generated were expressed as mean±standard error of the mean (SEM) from three independent experiments. Statistical comparison between different groups was performed by the unpaired Student&#39;s t-test. An asterisk indicates a significant difference (*, p&lt;0.05; **, p&lt;0.01; n.s., not significant). 
     The invention is not to be limited in scope by the specific embodiments described herein. Indeed, various modifications of the invention in addition to those described will become apparent to those skilled in the art from the foregoing description and accompanying figures. Such modifications are intended to fall within the scope of the appended claims. 
     All references cited herein are incorporated herein by reference in their entirety and for all purposes to the same extent as if each individual publication or patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety for all purposes. 
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     The foregoing description of the specific embodiments will so fully reveal the general nature of the disclosure that others can, by applying knowledge within the skill of the relevant art(s) (including the contents of the documents cited and incorporated by reference herein), readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present disclosure. Such adaptations and modifications are therefore intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance presented herein, in combination with the knowledge of one skilled in the relevant art(s). 
     While various embodiments of the present disclosure have been described above, it should be understood that they have been presented by way of examples, and not limitation. It would be apparent to one skilled in the relevant art(s) that various changes in form and detail could be made therein without departing from the spirit and scope of the disclosure. Thus, the present disclosure should not be limited by any of the above-described exemplary embodiments but should be defined only in accordance with the following claims and their equivalents.