bluuebunny/crossref_metadata_2025 huggingface dataset:
A novel, double mutation in DNA gyrase A of Escherichia coli conferring resistance to quinolone antibiotics
Authors: Truong Q C , Nguyen Van J C , Shlaes D , Gutmann L , Moreau N J
Published: October 2018

A spontaneous Escherichia coli mutant, named Q3, resistant to nalidixic acid was obtained from a previously described clinical isolate of E. coli, Q2, resistant to fluoroquinolones but susceptible to nalidixic acid (E. Cambau, F. Bordon, E. Collatz, and L. Gutmann, Antimicrob. Agents Chemother. 37:1247-1252, 1993). Q3 harbored the mutation Asp82Gly in addition to the Gly81Asp mutation of Q2. The different mutations leading to Gly81Asp, Asp82Gly, and Gly81AspAsp82Gly were introduced into the gyrA gene harbored on plasmid pJSW102, and the resulting plasmids were introduced into E. coli KNK453 (gyrAts) by transformation. The presence of Asp82Gly or Gly81Asp alone led to a low-level resistance to fluoroquinolones but not to nalidixic acid resistance. When both mutations were present, resistance to both nalidixic acid and fluoroquinolones was expressed. Purified gyrases of the different mutants showed similar rates of supercoiling. Dominance of the various gyrA mutant alleles harbored on plasmids was examined. The susceptibility to quinolones associated with wild-type gyrA was always dominant. The susceptibility to nalidixic acid expressed by the Gly81Asp mutant was dominant, while that expressed by the Asp82Gly mutant was recessive. From these results, we hypothesize that some amino acids within the quinolone resistance-determining region of gyrase A are more important for the association of subunits rather than for the activity of the holoenzyme.
The signal molecule for beta-lactamase induction in Enterobacter cloacae is the anhydromuramyl-pentapeptide
Authors: Dietz H , Pfeifle D , Wiedemann B
Published: October 2018

Beta-lactamase induction in Enterobacter cloacae, which is linked to peptidoglycan recycling, was investigated by high-performance liquid chromatographic analysis of cell wall fragments in genetically defined cells of Escherichia coli. After treatment of cells with beta-lactams, we detected an increase in a D-tripeptide (disaccharide-tripeptide, N-acetylglucosaminyl-1,6-anhydro-N-acetylmuramyl-L-alanyl-D-glutamyl-mes o-diaminopimelic acid), aD-tetrapeptide (disaccharide-tetrapeptide, N-acetylglucosaminyl-1,6-anhydro-N-acetylmuramyl-L-alanyl-D-glutamyl-mes o-diaminopimelic acid-D-alanine), and aD-pentapeptide (disaccharide-pentapeptide, N-acetylglucosaminyl-1,6-anhydro-N-acetylmuramyl-L-alanyl-D-glutamyl-mes o-diaminopimelic acid-D-alanyl-D-alanine)levels in the periplasms of bacterial cells. Furthermore, only the accumulation of aD-pentapeptide correlates with the beta-lactamase-inducing capacity of the beta-lactam antibiotic. The transmembrane protein AmpG transports all three aD-peptides into the cytoplasm, where they are degraded into the corresponding monosaccharide peptides. In the absence of AmpD the constitutive overproduction of beta-lactamase is accompanied by an accumulation of aM-tripeptide (monosaccharide-tripeptide, anhydro-N-acetylmuramyl-L-alanyl-D-glutamyl-meso-diaminopimelic acid) and aM-pentapeptide (L1,6-anhydro-N-acetylmuramyl-L-alanyl-D-glutamyl-meso-diaminopimelic acid-D-alanyl-D-alanine), but not aM-tetrapeptide (anhydro-N-acetylmuramyl-L-alanyl-D-glutamyl-meso-diaminopimelic acid-D-alanine), in the cytoplasm. Only the amount of aM-pentapeptide is increased upon treatment with imipenem. These findings indicate that aD-pentapeptide is the main periplasmic muropeptide, which is converted into the cytoplasmic signal molecule for beta-lactamase induction, the aM-pentapeptide.
The oxazolidinone eperezolid binds to the 50S ribosomal subunit and competes with binding of chloramphenicol and lincomycin
Authors: Lin A H , Murray R W , Vidmar T J , Marotti K R
Published: October 2018

The oxazolidinones are a novel class of antibiotics that act by inhibiting protein synthesis. It as been reported that the drug exerts its primary activity on the initiation phase of translation. In order to study the possibility of direct interaction between the drug and the ribosome, we have developed a binding assay using 14C-labelled eperezolid (PNU-100592; formerly U-100592). Eperezolid binds specifically to the 50S ribosomal subunit of Escherichia coli. The specific binding of eperezolid is dose dependent and is proportional to the ribosome concentrations. Scatchard analysis of the binding data reveals that the dissociation constant (Kd) is about 20 microM. The binding of eperezolid to the ribosome is competitively inhibited by chloramphenicol and lincomycin. However, unlike chloramphenicol and lincomycin, eperezolid does not inhibit the puromycin reaction, indicating that the oxazolidinones have no effect on peptidyl transferase. In addition, whereas lincomycin and, to some extent, chloramphenicol inhibit translation termination, eperezolid has no effect. Therefore, we conclude that the oxazolidinones inhibit protein synthesis by binding to the 50S ribosomal subunit at a site close to the site(s) to which chloramphenicol and lincomycin bind but that the oxazolidinones are mechanistically distinct from these two antibiotics.
The ketolide antibiotics HMR 3647 and HMR 3004 are active against Toxoplasma gondii in vitro and in murine models of infection
Authors: Araujo F G , Khan A A , Slifer T L , Bryskier A , Remington J S
Published: October 2018

Ketolides are a new class of macrolide antibiotics that have been shown to be active against a variety of bacteria including macrolide-resistant bacteria and mycobacteria. We examined two ketolides, HMR 3647 and HMR 3004, for their in vitro and in vivo activities against the protozoan parasite Toxoplasma gondii. In vitro, both ketolides at concentrations as low as 0.05 microg/ml markedly inhibited replication of tachyzoites of the RH strain within human foreskin fibroblasts. HMR 3004 demonstrated some toxicity for host cells after they were exposed to 5 microg of the drug per ml for 72 h. In contrast, HMR 3647 did not show any significant toxicity even at concentrations as high as 25 microg/ml. In vivo, both ketolides provided remarkable protection against death in mice lethally infected intraperitoneally with tachyzoites of the RH strain or orally with tissue cysts of the C56 strain of T. gondii. A dosage of 100 mg of HMR 3647 per kg of body weight per day administered for 10 days protected 50% of mice infected with tachyzoites. The same dosage of HMR 3004 protected 100% of the mice. In mice infected with cysts, a dosage of 30 mg of HMR 3647 per kg per day protected 100% of the mice, whereas a dosage of 40 mg of HMR 3004 per kg per day protected 75% of the mice. These results demonstrate that HMR 3647 and HMR 3004 possess excellent activities against two different strains of T. gondii and may be useful for the treatment of toxoplasmosis in humans.
Allicin from garlic strongly inhibits cysteine proteinases and cytopathic effects of Entamoeba histolytica
Authors: Ankri S , Miron T , Rabinkov A , Wilchek M , Mirelman D
Published: October 2018

The ability of Entamoeba histolytica trophozoites to destroy monolayers of baby hamster kidney cells is inhibited by allicin, one of the active principles of garlic. Cysteine proteinases, an important contributor to amebic virulence, as well as alcohol dehydrogenase, are strongly inhibited by allicin.
Preliminary animal pharmacokinetics of the parenteral antifungal agent MK-0991 (L-743,872)
Authors: Hajdu R , Thompson R , Sundelof J G , Pelak B A , Bouffard F A , Dropinski J F , Kropp H
Published: October 2018

MK-0991 (L-743,872) is a potent antifungal agent featuring long half-life pharmacokinetics. The pharmacokinetics of MK-0991 administered intravenously to mice, rats, rhesus monkeys, and chimpanzees is presented. Unique to MK-0991 is its consistent cross-species performance. The range of values for the pharmacokinetic parameters were as follows: clearance, 0.26 to 0.51 ml/min/kg; half-life, 5.2 to 7.6 h; and distributive volume, 0.11 to 0.27 liters/kg. The level of protein binding of MK-0991 was determined to be 96% in mouse and human serum. The compound exhibited high affinities for human serum albumin and at least two lipid components. The rationale for the selection of MK-0991 as a drug development candidate was based on its two- to threefold superior pharmacokinetic performance in chimpanzees over the performance of an otherwise equivalent analog, L-733,560. Once-daily dosing for MK-0991 is indicated by a graphical comparison of levels in the circulations of chimpanzees and mice. In a study of the pharmacokinetics of MK-0991 in mouse tissue, the organs were assayed following intraperitoneal administration. The area under the concentration-versus-time curves (AUC) segregated the tissues into three exposure categories relative to plasma. The tissues with greater exposure than that for plasma were liver (16 times), kidney (3 times), and large intestine (2 times). The exposure for small intestine, lung, and spleen were equivalent to that for plasma. Organs with lower levels of exposure were the heart (0.3 times that for plasma), thigh (0.2 times), and brain (0.06 times). Kinetically, drug was cleared more slowly from all tissues than from plasma, indicating that terminal-phase equilibrium had not been achieved by 24 h. Thus, some measure of accumulation is predicted for all tissues. Single daily doses of MK-0991 should provide adequate systemic levels of fungicidal activity as a result of its long half-life pharmacokinetics, wide distribution, and slowly accumulating concentrations in tissue.
Mutations in the dihydrofolate reductase gene of trimethoprim-resistant isolates of Streptococcus pneumoniae
Authors: Adrian P V , Klugman K P
Published: October 2018

Streptococcus pneumoniae isolates resistant to several antimicrobial agent classes including trimethoprim-sulfamethoxazole have been reported with increasing frequency throughout the world. The MICs of trimethoprim, sulfamethoxazole, and trimethoprim-sulfamethoxazole (1:19) for 259 clinical isolates from South Africa were determined, and 166 of these 259 (64%) isolates were resistant to trimethoprim-sulfamethoxazole (MICs > or =20 mg/liter). Trimethoprim resistance was found to be more strongly correlated with trimethoprim-sulfamethoxazole resistance (correlation coefficient, 0.744) than was sulfamethoxazole resistance (correlation coefficient, 0.441). The dihydrofolate reductase genes from 11 trimethoprim-resistant (MICs, 64 to 512 microg/ml) clinical isolates of Streptococcus pneumoniae were amplified by PCR, and the nucleotide sequences were determined. Two main groups of mutations to the dihydrofolate reductase gene were found. Both groups shared six amino acid changes (Glu20-Asp, Pro70-Ser, Gln81-His, Asp92-Ala, Ile100-Leu, and Leu135-Phe). The first group included two extra changes (Lys60-Gln and Pro111-Ser), and the second group was characterized by six additional amino acid changes (Glu14-Asp, Ile74-Leu, Gln91-His, Glu94-Asp, Phe147-Ser, and Ala149-Thr). Chromosomal DNA from resistant isolates and cloned PCR products of the genes encoding resistant dihydrofolate reductases were capable of transforming a susceptible strain of S. pneumoniae to trimethoprim resistance. The inhibitor profiles of recombinant dihydrofolate reductase from resistant and susceptible isolates revealed that the dihydrofolate reductase from trimethoprim-resistant isolates was 50-fold more resistant (50% inhibitory doses [ID50s], 3.9 to 7.3 microM) than that from susceptible strains (ID50s, 0.15 microM). Site-directed mutagenesis experiments revealed that one mutation, Ile100-Leu, resulted in a 50-fold increase in the ID50 of trimethoprim. The resistant dihydrofolate reductases were characterized by highly conserved redundant changes in the nucleotide sequence, suggesting that the genes encoding resistant dihydrofolate reductases may have evolved as a result of inter- or intraspecies recombination by transformation.
Pharmacokinetics of cefepime during continuous venovenous hemodiafiltration
Authors: Allaouchiche B , Breilh D , Jaumain H , Gaillard B , Renard S , Saux M C
Published: October 2018

The objective of this study was to analyze the pharmacokinetics of cefepime, in six patients with acute renal failure related to septic shock, during continuous venovenous hemodiafiltration (CVVHD) (Hemospal AN 69S hemofilter; Hospal, Lyon, France). Six patients, mean age 65 +/- 4 years (range, 61 to 69), were included and each received 2 g of cefepime by intravenous infusion over a 30-min period every 12 h. Prefilter serum, dialysate outlet (DO), and ultrafiltrate samples were collected 0.47, 0.50, 0.57, 1, 3, 5, 7, and 12 h after the beginning of infusion. The time design of samples was optimized in accordance with the theory of D optimality. The cefepime concentrations were measured by high-performance liquid chromatography. The pharmacokinetics computation was carried out using P-PHARM software. Mean serum concentration peaks were 53 +/- 21.9 mg/liter (range, 13.0 to 68.9) one-half hour after the infusion. The mean elimination half-life was 8.11 +/- 2.22 h (range, 4.76 to 10.84). DO clearance was 66.57 +/- 30.14 ml/min (range, 38.66 to 119.87). The mean volume of distribution was 0.71 +/- 0.37 liters/kg of body weight. CVVHD was effective for cefepime elimination. In these subjects, the elimination half-life and DO clearance were almost constant. The results of this study suggested that a 2-g twice-daily infusion (usual dosage) was required for an effective concentration in this group of patients.
Cloning and characterization of an aminoglycoside 6'-N-acetyltransferase gene from Citrobacter freundii which confers an altered resistance profile
Authors: Wu H Y , Miller G H , Blanco M G , Hare R S , Shaw K J
Published: October 2018

A novel gene encoding a 6'-N-aminoglycoside acetyltransferase, aac(6')-In, has been cloned and sequenced from Citrobacter freundii 13996-19, a clinical isolate from Venezuela. This gene mediates resistance to amikacin, 2'-N-ethylnetilmicin, isepamicin, kanamycin, netilmicin, and tobramycin. The aac(6')-In gene is 573 nucleotides in length and encodes a putative protein of 190 amino acids. AAC(6')-In is most closely related to AAC(6')-Im and AAC(6')-Ie, demonstrating 64.4% and 62.3% similarity, respectively, at the protein level, suggesting these proteins share a common ancestor. The aac(6')-In flanking sequences demonstrated homology to integron- and transposon-related elements which are often found associated with resistance determinants. Hybridization studies performed with an intragenic probe specific for aac(6')-In indicate that this gene is prevalent within Venezuela but has not been observed outside of the country. Furthermore, the aac(6)-In gene was found in 10 different species of gram-negative bacteria.
Pharmacokinetics of itraconazole (oral solution) in two groups of human immunodeficiency virus-infected adults with oral candidiasis
Authors: Reynes J , Bazin C , Ajana F , Datry A , Le Moing J P , Chwetzoff E , Levron J C
Published: October 2018

The pharmacokinetics of itraconazole formulated in a hydroxypropyl-beta-cyclodextrin oral solution was determined for two groups of human immunodeficiency virus (HIV)-infected adults with oral candidiasis (group A, 12 patients with CD4+ T-cell count of >200/mm3 and no AIDS, and group B, 11 patients with CD4+ T-cell count of <100/mm3 and AIDS). Patients received 100 mg of itraconazole every 12 h for 14 days. Concentrations of itraconazole and hydroxyitraconazole, the main active metabolite, were measured in plasma and saliva by high-performance liquid chromatography. Pharmacokinetic parameters determined at days 1 and 14 (the area under the concentration-time curve from 0 to 10 h, the maximum concentration of drug in plasma [Cmax], and the time to Cmax) were comparable in both groups. Trough levels in plasma (Cmin) were similar in both groups for the complete duration of the study. An effective concentration of itraconazole in plasma (>250 ng/ml) was reached at day 4. At day 14, Cmin values of itraconazole were 643 +/- 304 and 592 +/- 401 ng/ml for groups A and B, respectively, and Cmin values of hydroxyitraconazole were 1,411 +/- 594 and 1,389 +/- 804 ng/ml for groups A and B, respectively. In saliva, only unchanged itraconazole was detected, and mean concentrations were still high (>250 ng/ml) 4 h after the intake, which may contribute to the fast clinical response. In conclusion, the oral solution of itraconazole generates effective levels in plasma and saliva in HIV-infected patients; its relative bioavailability is not modified by the stage of HIV infection.
Comparison of in vitro antifungal susceptibilities of conidia and hyphae of filamentous fungi
Authors: Guarro J , Llop C , Aguilar C , Pujol I
Published: October 2018

The MICs and minimum fungicidal concentrations (MFCs) of amphotericin B, fluconazole, ketoconazole, flucytosine, miconazole, and itraconazole for 12 isolates of filamentous opportunistic fungi (Scopulariopsis sp., Paecilomyces sp., Cladosporium spp., and Cladophialophora sp.) were determined by a broth microdilution method with hyphal and conidial inocula. With hyphal inocula MICs and MFCs were practically always substantially higher. Only 25% of the 60 MIC comparisons showed discrepancies of twofold or less, while the remaining comparisons showed much larger differences.
Selection of multiple-antibiotic-resistant (mar) mutants of Escherichia coli by using the disinfectant pine oil: roles of the mar and acrAB loci
Authors: Moken M C , McMurry L M , Levy S B
Published: October 2018

Mutants of Escherichia coli selected for resistance to the disinfectant pine oil or to a household product containing pine oil also showed resistance to multiple antibiotics (tetracycline, ampicillin, chloramphenicol, and nalidixic acid) and overexpressed the marA gene. Likewise, antibiotic-selected Mar mutants, which also overexpress marA, were resistant to pine oil. Deletion of the mar or acrAB locus, the latter encoding a multidrug efflux pump positively regulated in part by MarA, increased the susceptibility of wild-type and mutant strains to pine oil.
A recombinant retroviral system for rapid in vivo analysis of human immunodeficiency virus type 1 susceptibility to reverse transcriptase inhibitors
Authors: Shi C , Mellors J W
Published: October 2018

We have developed a new recombinant retroviral system in which a library of infectious molecular clones of human immunodeficiency virus type 1 (HIV-1) is constructed with reverse transcriptase (RT) genes derived from viral RNA sequences in plasma. HIV-1 RT is amplified from plasma HIV-1 RNA by nested RT-PCR and cloned into a RT-defective HIV-1 proviral vector (xxLAI-np), generating 10(3) to 10(4) recombinant proviral clones from each reaction. The bulk cloning products or individual molecular clones are transfected into MT-2 cells to generate infectious virus. The resultant viruses are assayed for drug susceptibility in CD4+ cell lines to determine either the dominant phenotype of the recombinant virus mixture or the phenotypes of the individual viral clones. DNA sequencing of the cloned RT genes can identify mutations associated with phenotypic resistance of clonal mixtures or individual clones. This method can be used to rapidly detect the in vivo emergence of HIV-1 quasispecies resistant to RT inhibitors.
In vitro activities of doxycycline and enrofloxacin against European Chlamydia psittaci strains from turkeys
Authors: Butaye P , Ducatelle R , De Backer P , Vermeersch H , Remon J P , Haesebrouck F
Published: October 2018

The in vitro susceptibility of 14 European Chlamydia psittaci strains from turkeys to the antibiotics doxycycline and enrofloxacin was tested. For doxycycline the MIC ranged from 0.05 to 0.2 microg/ml, with an average of 0.1 microg/ml. For enrofloxacin the MIC was 0.25 microg/ml. Acquired resistance was not detected against doxycycline and enrofloxacin.
In vitro evaluation of antibiotic diffusion from antibiotic-impregnated biodegradable beads and polymethylmethacrylate beads
Authors: Mader J T , Calhoun J , Cobos J
Published: October 2018

Antibiotic-impregnated beads are used in the dead bone space following debridement surgery to deliver local, high concentrations of antibiotics. Polymethylmethacrylate (PMMA), 2,000-molecular-weight (MW) polylactic acid (PLA), Poly(DL-lactide)-coglycolide (PL:CG; 90:10, 80:20, and 70:30), and the combination 2,000-MW PLA-70:20 PL:CG were individually mixed with clindamycin, tobramycin, or vancomycin. Beads were placed in 1 ml of phosphate-buffered saline (PBS) and incubated at 37 degrees C. The PBS was changed daily, and the removed PBS samples were stored at -70 degrees C until the antibiotic in each sample was determined by microbiological disk diffusion assay. Nondissolving PMMA beads with tobramycin and clindamycin had concentrations well above breakpoint sensitivity concentrations (i.e., the antibiotic concentrations at the transition point between bacterial killing and resistance to the antibiotic) for more than 90 days, but vancomycin concentrations dropped by day 12. ALl PLA, PL:CG, and the 2,000-MW PLA-70:30 PL:CG biodegradable beads release high concentrations of all the antibiotics in vitro for the period of time needed to treat bone infections (i.e., 4 to 8 weeks). Antibiotic-loaded PLA and PL:CG beads have the advantage of better antibiotic elution and the ability to biodegradable (thereby averting the need for secondary surgery for bead removal) compared to the PMMA beads presently used in the clinical setting.
Comparative in vitro activities of trovafloxacin (CP 99,219) and other antimicrobials against clinically significant anaerobes
Authors: Aldridge K E , Ashcraft D , Bowman K A
Published: October 2018

A total of 590 strains of clinically important anaerobes were tested to determine their susceptibility to trovafloxacin. Overall, trovafloxacin had a mode MIC of 0.25 micrograms/ml and a MIC at which 90% of the isolates were inhibited of 1 micrograms/ml and had activity comparable to that of metronidazole. Trovafloxacin was 8-, 8-, 16-, 32-, and 64-fold more active than ampicillin-sulbactam, clindamycin, ciprofloxacin, cefoxitin, and cefotetan, respectively. Of the Bacteroides fragilis group, 97% of the isolates were inhibited by trovafloxacin at 21 micrograms/ml, and trovafloxacin was more active than ciprofloxacin, cefoxitin, cefotetan, ampicillin-sulbactam, and clindamycin against Clostridium, Fusobacterium, Porphyromonas, and Prevotella strains.
Activities of various compounds against murine and primate polyomaviruses
Authors: Andrei G , Snoeck R , Vandeputte M , De Clercq E
Published: October 2018

Polyomavirus infections in humans are due to BK virus (BKV) and JC virus (JCV). Diseases associated with human polyomaviruses occur mostly in immunocompromised adults, e.g., progressive multifocal leukoencephalopathy (PML), caused by JCV, in AIDS patients and hemorrhagic cystitis and uretral stenosis, caused by BKV, in transplant recipients. No therapy is available for these diseases, which necessitates the development of chemical entities that are active against polyomaviruses. Several antiviral compounds were evaluated to determine their effects on the in vitro replication of mouse polyomavirus and the primate viruses simian virus 40 (SV40), SV40 PML-1, and SV40 PML-2. The activity of the different compounds was assessed by a cytopathic effect reduction assay and confirmed in a virus yield assay. Cidofovir [HPMPC; (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine] and its cyclic counterpart emerged as the most selective antipolyomavirus agents. The 50% inhibitory concentrations for HPMPC were in the range of 4 to 7 micrograms/ml, and its selectivity index varied from 11 to 20 for mouse polyomavirus and from 23 to 33 for SV40 strains in confluent cell monolayers. Cell cytotoxicity was up to 15-fold greater in growing cells. Other acyclic nucleoside phosphonates (i.e., HPMPA; [(S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine] and PMEG [9-(2-phosphonylmethoxyethyl)-guanine]) also showed some activity but had low selectivity. None of the other drugs tested against these animal viruses (i.e., acyclovir, ganciclovir, brivudine, ribavirin, foscarnet, and cytarabine) showed significant activity. Thus, HPMPC deserves further evaluation as a candidate drug for polyomavirus infections in the immunocompromised host.
Antiretroviral activities of acyclic nucleoside phosphonates [9-(2-phosphonylmethoxyethyl)adenine, 9-(2-phosphonylmethoxyethyl)guanine, (R)-9-(2-phosphonylmethoxypropyl)adenine, and MDL 74,968] in cell cultures and murine sarcoma virus-infected newborn NMRI mice
Authors: Balzarini J , Vahlenkamp T , Egberink H , Hartmann K , Witvrouw M , Pannecouque C , Casara P , Navé J F , De Clercq E
Published: October 2018

From a side-by-side comparative study, the acyclic nucleoside phosphonates (R)-9-(2-phosphonylmethoxypropyl)adenine [(R)-PMPA] and 9-(2-methylidene-3-phosphonomethoxypropyl)guanine (MDL 74,968) proved more selective in their inhibitory effect on human immunodeficiency virus types 1 and 2, feline immunodeficiency virus, and Moloney murine sarcoma virus (MSV) in cell cultures than the 9-(2-phosphonylmethoxyethyl) derivatives of adenine (PMEA) and guanine (PMEG). In particular, PMEG proved quite toxic. PMEA, (R)-PMPA, and MDL 74,968 afforded a marked delay in MSV-induced tumor initiation in MSV-infected newborn NMRI mice and substantially delayed associated animal death at doses as low as 4 to 10 mg/kg of body weight. Treatment of the NMRI mice with PMEA, (R)-PMPA, and MDL 74,968 at 25 or 50 mg/kg resulted in a high percentage of long-term survivors.
Antifungal drug susceptibilities of oral Candida dubliniensis isolates from human immunodeficiency virus (HIV)-infected and non-HIV-infected subjects and generation of stable fluconazole-resistant derivatives in vitro
Authors: Moran G P , Sullivan D J , Henman M C , McCreary C E , Harrington B J , Shanley D B , Coleman D C
Published: October 2018

Candida dubliniensis is a recently described species of Candida associated with oral candidiasis in human immunodeficiency virus (HIV)-infected individuals. Nineteen oral isolates of C. dubliniensis recovered from 10 HIV-positive and 4 HIV-negative individuals and one vaginal isolate from an additional HIV-negative subject were assessed for fluconazole susceptibility by broth microdilution (BMD), hyphal elongation assessment, and Etest. The susceptibilities of these 20 isolates to itraconazole and amphotericin B and of 10 isolates to ketoconazole were also determined by BMD only. Sixteen of the C. dubliniensis isolates were susceptible to fluconazole (MIC range, 0.125 to 1.0 microgram ml-1), and four (recovered from two AIDS patients) were fluconazole resistant (MIC range, 8 to 32 micrograms ml-1). Fluconazole susceptibility data obtained by hyphal elongation assessment correlated well with results obtained by BMD, but the corresponding Etest MIC results were one to four times higher. All of the isolates tested were found to be sensitive to itraconazole, ketoconazole, and amphotericin B. Sequential exposure of two fluconazole-sensitive (MIC, 0.5 microgram ml-1) C. dubliniensis isolates to increasing concentrations of fluconazole in agar medium resulted in the recovery of derivatives which expressed a stable fluconazole-resistant phenotype (BMD-determined MIC range, 16 to 64 micrograms ml-1), even after a minimum of 10 consecutive subcultures on drug-free medium and following prolonged storage at -70 degrees C. The clonal relationship between the parental isolates and their respective fluconazole-resistant derivatives was confirmed by genomic DNA fingerprinting and karyotype analysis. The results of this study demonstrate that C. dubliniensis is inherently susceptible to commonly used antifungal drugs, that fluconazole resistance does occur in clinical isolates, and that stable fluconazole resistance can be readily induced in vitro following exposure to the drug.
Pharmacokinetic enhancement of inhibitors of the human immunodeficiency virus protease by coadministration with ritonavir
Authors: Kempf D J , Marsh K C , Kumar G , Rodrigues A D , Denissen J F , McDonald E , Kukulka M J , Hsu A , Granneman G R , Baroldi P A , Sun E , Pizzuti D , Plattner J J , Norbeck D W , Leonard J M
Published: October 2018

Coadministration with the human immunodeficiency virus (HIV) protease inhibitor ritonavir was investigated as a method for enhancing the levels of other peptidomimetic HIV protease inhibitors in plasma. In rat and human liver microsomes, ritonavir potently inhibited the cytochrome P450 (CYP)-mediated metabolism of saquinavir, indinavir, nelfinavir, and VX-478. The structural features of ritonavir responsible for CYP binding and inhibition were examined. Coadministration of other protease inhibitors with ritonavir in rats and dogs produced elevated and sustained plasma drug levels 8 to 12 h after a single dose. Drug exposure in rats was elevated by 8- to 46-fold. A > 50-fold enhancement of the concentrations of saquinavir in plasma was observed in humans following a single codose of ritonavir (600 mg) and saquinavir (200 mg). These results indicate that ritonavir can favorably alter the pharmacokinetic profiles of other protease inhibitors. Combination regimens of ritonavir and other protease inhibitors may thus play a role in the treatment of HIV infection. Because of potentially substantial drug level increases, however, such combinations require further investigation to establish safe regimens for clinical use.
Activity of liposomal amphotericin B against experimental cutaneous leishmaniasis
Authors: Yardley V , Croft S L
Published: October 2018

The polyene antibiotic amphotericin B is currently a second-line treatment for visceral leishmaniasis (VL) and mucocutaneous leishmaniasis. Lipid-amphotericin B formulations with lower toxicity than the parent drug that were developed for the treatment of systemic mycoses have proved to be an effective treatment for VL, especially AmBisome, a small unilamellar negatively charged liposome. In vitro, free amphotericin B was three to six times more active than the liposomal formulation AmBisome against both Leishmania major promastigotes in culture and amastigotes in murine macrophages. In a BALB/c L. major model of cutaneous infection, liposomal amphotericin B administered once a day on six alternate days by the intravenous route produced a dose-response effect between 6.25 and 50 mg/kg. Liposomal amphotericin B administered subcutaneously close to a lesion had no significant activity. Free drug was ineffective at nontoxic doses. The results suggest that liposomal amphotericin B may be useful in the treatment of cutaneous leishmaniasis.
Improved activity of a synthetic indolicidin analog
Authors: Falla T J , Hancock R E
Published: October 2018

A novel cationic peptide, CP-11, based on the structure of the bovine neutrophil peptide indolicidin, was designed to increase the number of positively charged residues, maintain the short length (13 amino acids), and enhance the amphipathicity relative to those of indolicidin. CP-11, and especially its carboxymethylated derivative, CP-11C, demonstrated improved activity against gram-negative bacteria and Candida albicans, while it maintained the activity of indolicidin against staphylococci and demonstrated a reduced ability to lyse erythrocytes. In Escherichia coli, CP-11 was better able than indolicidin to permeabilize both the outer membrane, as indicated by the enhancement of uptake of 1-N-phenylnaphthylamine, and the inner membrane, as determined by the unmasking of cytoplasmic beta-galactosidase, providing an explanation for its improved activity.
Comparative study of bactericidal activities, postantibiotic effects, and effects of bacterial virulence of penicillin G and six macrolides against Streptococcus pneumoniae
Authors: Fuursted K , Knudsen J D , Petersen M B , Poulsen R L , Rehm D
Published: October 2018

In this report, we present MIC, bactericidal activity, postantibiotic effect (PAE), and in vivo infectivity data for postantibiotic-phase pneumococci. We compared and evaluated penicillin G and six macrolides, erythromycin, azithromycin, clarithromycin, dirithromycin, roxithromycin, and spiramycin, against 10 strains of pneumococci with various levels of susceptibility to penicillin. All of the agents, except azithromycin, exhibited a bactericidal effect (a > or = 3 log10 decrease in the number of CFU per milliliter) after 4 h of exposure to a concentration equal to 10 times the MIC, displaying the following hierarchy: spiramycin = penicillin G = erythromycin = dirithromycin = clarithromycin = roxithromycin > azithromycin. The bactericidal rate of penicillin G was significantly lower for resistant strains (MIC, > or = 2 microg/ml), while bactericidal rates of macrolides were unaffected by penicillin susceptibility. A PAE was induced in all of the strains by all of the antibiotics after exposure for 1 h to a concentration equivalent to 10 times the MIC. The mean duration of PAEs varied between 2.3 and 3.9 h, showing the following hierarchy: spiramycin = dirithromycin = clarithromycin = erythromycin = roxithromycin > azithromycin > penicillin G. Virulence studies were performed with immunocompetent mice by intraperitoneal inoculation of virulent, penicillin-susceptible serotype 3 pneumococci which had been pre-exposed to penicillin G or a macrolide for 1 h. A significant decrease in the virulence of postantibiotic-phase pneumococci was induced only by erythromycin, azithromycin, dirithromycin, and spiramycin, displaying 5.9-, 7.1-, 4.2-, and 3.6-fold increases in the 50% lethal dose (LD50) compared to a control suspension, respectively. No significant correlation could be demonstrated between the LD50 and the MIC, bactericidal activity, or PAE duration. These results suggest that antimicrobial interaction with host defenses in terms of virulence might be a significant parameter that could influence the drug or drug regimen of choice.
An axenic amastigote system for drug screening
Authors: Callahan H L , Portal A C , Devereaux R , Grogl M
Published: October 2018

Currently available primary screens for selection of candidate antileishmanial compounds are not ideal. The choices include screens that are designed to closely reflect the situation in vivo but are labor-intensive and expensive (intracellular amastigotes and animal models) and screens that are designed to facilitate rapid testing of a large number of drugs but do not use the clinically relevant parasite stage (promastigote model). The advent of successful in vitro culture of axenic amastigotes permits the development of a primary screen which is quick and easy like the promastigote screen but still representative of the situation in vivo, since it uses the relevant parasite stage. We have established an axenic amastigote drug screening system using a Leishmania mexicana strain (strain M379). A comparison of the 50% inhibitory concentration (IC50) drug sensitivity profiles of M379 promastigotes, intracellular amastigotes, and axenic amastigotes for six clinically relevant antileishmanial drugs (sodium stibogluconate, meglumine antimoniate, pentamidine, paromomycin, amphotericin B, WR6026) showed that M379 axenic amastigotes are a good model for a primary drug screen. Promastigote and intracellular amastigote IC50s differed for four of the six drugs tested by threefold or more; axenic amastigote and intracellular amastigote IC50s differed by twofold for only one drug. This shows that the axenic amastigote susceptibility to clinically used reference drugs is comparable to the susceptibility of amastigotes in macrophages. These data also suggest that for the compounds tested, susceptibility is intrinsic to the parasite stage. This contradicts previous hypotheses that suggested that the activities of antimonial agents against intracellular amastigotes were solely a function of the macrophage.
Susceptibilities of 228 penicillin- and erythromycin-susceptible and -resistant pneumococci to RU 64004, a new ketolide, compared with susceptibilities to 16 other agents
Authors: Ednie L M , Spangler S K , Jacobs M R , Appelbaum P C
Published: October 2018

The susceptibilities of 228 penicillin- and erythromycin-susceptible and -resistant pneumococci to RU 64004, a new ketolide, were tested by agar dilution, and the results were compared with those for penicillin G, erythromycin, azithromycin, clarithromycin, rokitamycin, clindamycin, pristinamycin, ciprofloxacin, sparfloxacin, trimethoprim-sulfamethoxazole, doxycycline, chloramphenicol, cefuroxime, ceftriaxone, imipenem, and vancomycin. RU 64004 was very active against all strains tested, with MICs at which 90% of the isolates are inhibited (MIC90s) of 0.016 microg/ml for erythromycin-susceptible strains (MIC, < or = 0.25 microg/ml) and 0.25 microg/ml for erythromycin-resistant strains (MIC, > or = 0.5 microg/ml). All other macrolides had MIC90s of 0.03 to 0.25 and > or = 128 microg/ml for erythromycin-susceptible and -resistant strains, respectively. Among erythromycin-resistant strains, clindamycin MICs for 28 of 91 (30.7%) were < or = 0.125 microg/ml. Pristinamycin MICs for all strains were < or = 1.0 microg/ml. MIC90s of ciprofloxacin and sparfloxacin were 4.0 and 0.25 microg/ml, respectively, and were unaffected by susceptibility to penicillin or erythromycin. Vancomycin and imipenem inhibited all strains at < or = 0.5 and < or = 0.25 microg/ml, respectively. MICs of cefuroxime and cefotaxime rose with those of penicillin G. MICs of trimethoprim-sulfamethoxazole, doxycycline, and chloramphenicol were variable but were generally higher for penicillin- and erythromycin-resistant strains. RU 64004 is the first member of the macrolide group which has low MICs for erythromycin-resistant pneumococci.
Antibacterial effect of the adhering human Lactobacillus acidophilus strain LB
Authors: Coconnier M H , Liévin V , Bernet-Camard M F , Hudault S , Servin A L
Published: October 2018

The spent culture supernatant of the human Lactobacillus acidophilus strain LB produces an antibacterial activity against a wide range of gram-negative and gram-positive pathogens. It decreased the in vitro viability of Staphylococcus aureus, Listeria monocytogenes, Salmonella typhimurium, Shigella flexneri, Escherichia coli, Klebsiella pneumoniae, Bacillus cereus, Pseudomonas aeruginosa, and Enterobacter spp. In contrast, it did not inhibit lactobacilli and bifidobacteria. The activity was heat stable and relatively sensitive to enzymatic treatments and developed under acidic conditions. The antimicrobial activity was independent of lactic acid production. Activity against S. typhimurium SL1344 infecting human cultured intestinal Caco-2 cells was observed as it was in the conventional C3H/He/oujco mouse model with S. typhimurium C5 infection and oral treatment with the LB spent culture supernatant.
Antiviral activity of the dihydropyrone PNU-140690, a new nonpeptidic human immunodeficiency virus protease inhibitor
Authors: Poppe S M , Slade D E , Chong K T , Hinshaw R R , Pagano P J , Markowitz M , Ho D D , Mo H , Gorman R R , Dueweke T J , Thaisrivongs S , Tarpley W G
Published: October 2018

PNU-140690 is a member of a new class of nonpeptidic human immunodeficiency virus (HIV) protease inhibitors (sulfonamide-containing 5,6-dihydro-4-hydroxy-2-pyrones) discovered by structure-based design. PNU-140690 has excellent potency against a variety of HIV type 1 (HIV-1) laboratory strains and clinical isolates, including those resistant to the reverse transcriptase inhibitors zidovudine or delavirdine. When combined with either zidovudine or delavirdine, PNU-140690 contributes to synergistic antiviral activity. PNU-140690 is also highly active against HIV-1 variants resistant to peptidomimetic protease inhibitors, underscoring the structural distinctions between PNU-140690 and substrate analog protease inhibitors. PNU-140690 retains good antiviral activity in vitro in the presence of human plasma proteins, and preclinical pharmacokinetic studies revealed good oral bioavailability. Accordingly, PNU-140690 is a candidate for clinical evaluation.
Emergence of the trimethoprim resistance gene dfrD in Listeria monocytogenes BM4293
Authors: Charpentier E , Courvalin P
Published: October 2018

The sequence of the trimethoprim resistance gene of the 3.7-kb plasmid (pIP823) that confers high-level resistance (MIC, 1,024 microg/ml) to Listeria monocytogenes BM4293 was determined. The gene was identical to dfrD recently detected in Staphylococcus haemolyticus MUR313. The corresponding protein, S2DHFR, represents the second class of high-level trimethoprim-resistant dihydrofolate reductase identified in gram-positive bacteria. We propose that trimethoprim resistance in L. monocytogenes BM4293 could originate in staphylococci.
Efficacies of ofloxacin, rifampin, and clindamycin in treatment of Staphylococcus aureus abscesses and correlation with results of an in vitro assay of intracellular bacterial killing
Authors: Bamberger D M , Herndon B L , Dew M , Chern R P , Mitchell H , Summers L E , Marcus R F , Kim S C , Suvarna P R
Published: October 2018

We studied the efficacies of ofloxacin, rifampin, and clindamycin in a Staphylococcus aureus abscess model and seven antimicrobial regimens in an intracellular killing assay. Ofloxacin plus rifampin was the most effective regimen in the abscess model, and rifampin and ofloxacin were the most active regimens in the intracellular killing assay.
Multiple-dose pharmacokinetics of ritonavir in human immunodeficiency virus-infected subjects
Authors: Hsu A , Granneman G R , Witt G , Locke C , Denissen J , Molla A , Valdes J , Smith J , Erdman K , Lyons N , Niu P , Decourt J P , Fourtillan J B , Girault J , Leonard J M
Published: October 2018

The multiple-dose pharmacokinetics of ritonavir were investigated in four groups of human immunodeficiency virus-positive male subjects (with 16 subjects per group) under nonfasting conditions; a 3:1 ritonavir:placebo ratio was used. Ritonavir was given at 200 (group I), 300 (group II), 400 (group III), or 500 (group IV) mg every 12 h for 2 weeks. The multiple-dose pharmacokinetics of ritonavir were moderately dose dependent, with the clearance for group IV (6.8 +/- 2.7 liters/h) being an average of 32% lower than that for group I (10.0 +/- 3.2 liters/h). First-pass metabolism should be minimal for ritonavir. The functional half-life, estimated from peak and trough concentrations, were similar among the dosage groups, averaging 3.1 and 5.7 h after the morning and evening doses, respectively. The area under the concentration-time curve at 24 h (AUC24) and apparent terminal-phase elimination rate constant remained relatively time invariant, but predose concentrations decreased 30 to 70% over time. Concentration-dependent autoinduction is the most likely mechanism for the time-dependent pharmacokinetics. The Km and initial maximum rate of metabolism (Vmax) values estimated from population pharmacokinetic modeling (nonlinear mixed-effects models) were 3.43 microg/ml and 46.9 mg/h, respectively. The group IV Vmax increased to 68 mg/h after 2 weeks. The maximum concentration of ritonavir in serum (Cmax) and AUC after the evening doses were an average of 30 to 40% lower than the values after the morning doses, while the concentration at 12 h was an average of 32% lower than the predose concentration, probably due to protracted absorption. Less than 2% of the dose was eliminated unchanged in the urine. Triglyceride levels increased from the levels at the baseline, and the levels were correlated with baseline triglyceride levels and AUC, Cmax, or predose concentrations.
Increased expression of fibronectin-binding proteins by fluoroquinolone-resistant Staphylococcus aureus exposed to subinhibitory levels of ciprofloxacin
Authors: Bisognano C , Vaudaux P E , Lew D P , Ng E Y , Hooper D C
Published: October 2018

Bacterial adhesion, which plays an important role in Staphylococcus aureus colonization and infection, may be altered by the presence of antibiotics or/and antibiotic resistance determinants. This study evaluated the effect of fluoroquinolone resistance determinants on S. aureus adhesion to solid-phase fibronectin, which is specifically mediated by two surface-located fibronectin-binding proteins. Five isogenic mutants, derived from strain NCTC 8325 and expressing various levels of quinolone resistance, were tested in an in vitro bacterial adhesion assay with polymethylmethacrylate coverslips coated with increasing amounts of fibronectin. These strains contained single or combined mutations in the three major loci contributing to fluoroquinolone resistance, namely, grlA, gyrA, and flqB, which code for altered topoisomerase IV, DNA gyrase, and increased norA-mediated efflux of fluoroquinolones, respectively. Adhesion characteristics of the different quinolone-resistant mutants grown in the absence of fluoroquinolone showed only minor differences from those of parental strains. However, more important changes in adhesion were exhibited by mutants highly resistant to quinolones following their exponential growth in the presence of one-quarter MIC of ciprofloxacin. Increased bacterial adhesion of the highly quinolone-resistant mutants, which contained combined mutations in grlA and gyrA, was associated with and explained by the overexpression of their fibronectin-binding proteins as assessed by Western ligand affinity blotting. These findings contradict the notion that subinhibitory concentrations of antibiotics generally decrease the expression of virulence factors by S. aureus. Perhaps the increased adhesion of S. aureus strains highly resistant to fluoroquinolones contributes in part to that emergence in clinical settings.
Comparison of the postantibiotic and postantibiotic sub-MIC effects of levofloxacin and ciprofloxacin on Staphylococcus aureus and Streptococcus pneumoniae
Authors: Licata L , Smith C E , Goldschmidt R M , Barrett J F , Frosco M
Published: October 2018

The postantibiotic subminimum inhibitory concentration effect (PA SME) may simulate in vivo drug exposure more accurately than the postantibiotic effect (PAE) since subinhibitory concentrations of drug persist between antibiotic dosings. In this study, we compared the PAEs and PA SMEs of levofloxacin and ciprofloxacin for clinical isolates of fluoroquinolone-susceptible Staphylococcus aureus and Streptococcus pneumoniae. At two times the MIC, PAEs of levofloxacin were an average of 0.6 h longer than the PAEs obtained for ciprofloxacin for methicillin-susceptible and methicillin-resistant S. aureus strains. The PAEs of levofloxacin and ciprofloxacin ranged from 1.8 to 3.1 and 1.1 to 2.4 h, respectively. Continued exposure of the methicillin-resistant strain to 1/16, 1/8, and 1/4 the MIC resulted in PA SMEs of 6.5, 15.3, and >22.3 h, respectively, for levofloxacin and 3.8, 8.0, and 12.3 h, respectively, for ciprofloxacin. For isolates of S. pneumoniae, at two times the MIC of both fluoroquinolones, the average PAEs of levofloxacin and ciprofloxacin were equivalent: 1.3 h for the penicillin-susceptible isolate and 0.6 h for the penicillin-resistant isolate. Continued exposure of the penicillin-susceptible S. pneumoniae strain to 1/16, 1/8, and 1/4 the MIC resulted in average PA SMEs of 1.0, 1.4, and 2.8 h, respectively, for levofloxacin and 1.8, 2.0, and 2.5 h, respectively, for ciprofloxacin. Continued exposure of penicillin-resistant S. pneumoniae to 1/16, 1/8, and 1/4 the MIC of the same fluoroquinolones resulted in average PA SMEs of 0.6, 1.1, and 2.9 h, respectively, for levofloxacin and 0.6, 1.1, and 1.5 h, respectively, for ciprofloxacin. The PA SMEs observed demonstrate the superior activity of levofloxacin against methicillin-susceptible or methicillin-resistant S. aureus. Although PAEs were similar for the penicillin-susceptible and penicillin-resistant S. pneumoniae strains, the PA SME of levofloxacin at one-fourth the MIC was longer for penicillin-resistant S. pneumoniae.