bluuebunny/crossref_metadata_2025_split huggingface dataset:
Activities of Tobramycin and Polymyxin E against Pseudomonas aeruginosa Biofilm-Coated Medical Grade Endotracheal Tubes
Authors: Tarquinio Keiko , Confreda Kelsey , Shurko James , LaPlante Kerry 
Published: December 2013

ABSTRACT

Indwelling medical devices have become a major source of nosocomial infections, especially
Pseudomonas aeruginosa
infections, which remain the most common cause of ventilator-associated pneumonia (VAP) in neonates and children. Using medical grade polyvinyl chloride endotracheal tubes (ETTs), the activity of tobramycin and polymyxin E was quantified in a simulated prevention and treatment static time-kill model using biofilm-forming
P. aeruginosa
. The model simulated three clinical conditions: (i) planktonic bacteria grown in the presence of antibiotics (tobramycin and polymyxin E) without ETTs, (ii) planktonic bacteria grown in the presence of
P. aeruginosa
, antibiotic, and ETTs (simulating prevention), and (iii) a 24-h-formed
P. aeruginosa
biofilm grown on ETTs prior to antibiotic exposure (simulating treatment). In the model simulating “prevention” (conditions 1 and 2 above), tobramycin alone or in combination with polymyxin E was more bactericidal than polymyxin E alone at 24 h using a concentration of greater than 2 times the MIC. However, after a 24-h-old biofilm was allowed to form on the ETTs, neither monotherapy nor combination therapy over 24 h exhibited bactericidal or bacteriostatic effects. Against the same pathogens, tobramycin and polymyxin E, alone or in combination, exhibited bactericidal activity prior to biofilm attachment to the ETTs; however, no activity was observed once biofilm formed on ETTs. These findings support surveillance culturing to identify pathogens for a rapid and targeted approach to therapy, especially when
P. aeruginosa
is a potential pathogen.
Evaluation of DNA Primase DnaG as a Potential Target for Antibiotics
Authors: Kuron Aneta , Korycka-Machala Malgorzata , Brzostek Anna , Nowosielski Marcin , Doherty Aidan , Dziadek Bozena , Dziadek Jaroslaw 
Published: December 2013

ABSTRACT

Mycobacteria contain genes for several DNA-dependent RNA primases, including
dnaG
, which encodes an essential replication enzyme that has been proposed as a target for antituberculosis compounds. An
in silico
analysis revealed that mycobacteria also possess archaeo-eukaryotic superfamily primases (AEPs) of unknown function. Using a homologous recombination system, we obtained direct evidence that wild-type
dnaG
cannot be deleted from the chromosome of
Mycobacterium smegmatis
without disrupting viability, even in backgrounds in which mycobacterial AEPs are overexpressed. In contrast, single-deletion AEP mutants or mutants defective for all four identified
M. smegmatis
AEP genes did not exhibit growth defects under standard laboratory conditions. Deletion of native
dnaG
in
M. smegmatis
was tolerated only after the integration of an extra intact copy of the
M. smegmatis
or
Mycobacterium tuberculosis
dnaG
gene, under the control of chemically inducible promoters, into the
attB
site of the chromosome.
M. tuberculosis
and
M. smegmatis
DnaG proteins were overproduced and purified, and their primase activities were confirmed using radioactive RNA synthesis assays. The enzymes appeared to be sensitive to known inhibitors (suramin and doxorubicin) of DnaG. Notably,
M. smegmatis
bacilli appeared to be sensitive to doxorubicin and resistant to suramin. The growth and survival of conditional mutant mycobacterial strains in which DnaG was significantly depleted were only slightly affected under standard laboratory conditions. Thus, although DnaG is essential for mycobacterial viability, only low levels of protein are required for growth. This suggests that very efficient inhibition of enzyme activity would be required for mycobacterial DnaG to be useful as an antibiotic target.
Genomics of KPC-Producing Klebsiella pneumoniae Sequence Type 512 Clone Highlights the Role of RamR and Ribosomal S10 Protein Mutations in Conferring Tigecycline Resistance
Authors: Villa Laura , Feudi Claudia , Fortini Daniela , García-Fernández Aurora , Carattoli Alessandra 
Published: December 2013

ABSTRACT

Full genome sequences were determined for five
Klebsiella pneumoniae
strains belonging to the sequence type 512 (ST512) clone, producing KPC-3. Three strains were resistant to tigecycline, one showed an intermediate phenotype, and one was susceptible. Comparative analysis performed using the genome of the susceptible strain as a reference sequence identified genetic differences possibly associated with resistance to tigecycline. Results demonstrated that mutations in the
ramR
gene occurred in two of the three sequenced strains. Mutations in RamR were previously demonstrated to cause overexpression of the AcrAB-TolC efflux system and were implicated in tigecycline resistance in
K. pneumoniae
. The third strain showed a mutation located at the vertex of a very well conserved loop in the S10 ribosomal protein, which is located in close proximity to the tigecycline target site in the 30S ribosomal subunit. This mutation was previously shown to be associated with tetracycline resistance in
Neisseria gonorrhoeae
. A PCR-based approach was devised to amplify the potential resistance mechanisms identified by genomics and applied to two additional ST512 strains showing resistance to tigecycline, allowing us to identify mutations in the
ramR
gene.
Role of P-Glycoprotein in the Distribution of the HIV Protease Inhibitor Atazanavir in the Brain and Male Genital Tract
Authors: Robillard Kevin R. , Chan Gary N. Y. , Zhang Guijin , la Porte Charles , Cameron William , Bendayan Reina 
Published: December 2013

ABSTRACT

The blood-testis barrier and blood-brain barrier are responsible for protecting the male genital tract and central nervous system from xenobiotic exposure. In HIV-infected patients, low concentrations of antiretroviral drugs in cerebrospinal fluid and seminal fluid have been reported. One mechanism that may contribute to reduced concentrations is the expression of ATP-binding cassette drug efflux transporters, such as P-glycoprotein (P-gp). The objective of this study was to investigate
in vivo
the tissue distribution of the HIV protease inhibitor atazanavir in wild-type (WT) mice, P-gp/breast cancer resistance protein (Bcrp)-knockout (
Mdr1a
−/−
,
Mdr1b
−/−
, and
Abcg2
−/−
triple-knockout [TKO]) mice, and Cyp3a
−/−
(Cyp) mice. WT mice and Cyp mice were pretreated with a P-gp/Bcrp inhibitor, elacridar (5 mg/kg of body weight), and the HIV protease inhibitor and boosting agent ritonavir (2 mg/kg intravenously [i.v.]), respectively. Atazanavir (10 mg/kg) was administered i.v. Atazanavir concentrations in plasma (
C
plasma
), brain (
C
brain
), and testes (
C
testes
) were quantified at various times by liquid chromatography-tandem mass spectrometry. In TKO mice, we demonstrated a significant increase in atazanavir
C
brain
/
C
plasma
(5.4-fold) and
C
testes
/
C
plasma
(4.6-fold) ratios compared to those in WT mice (
P
< 0.05). Elacridar-treated WT mice showed a significant increase in atazanavir
C
brain
/
C
plasma
(12.3-fold) and
C
testes
/
C
plasma
(13.5-fold) ratios compared to those in vehicle-treated WT mice. In Cyp mice pretreated with ritonavir, significant (
P
< 0.05) increases in atazanavir
C
brain
/
C
plasma
(1.8-fold) and
C
testes
/
C
plasma
(9.5-fold) ratios compared to those in vehicle-treated WT mice were observed. These data suggest that drug efflux transporters, i.e., P-gp, are involved in limiting the ability of atazanavir to permeate the rodent brain and genital tract. Since these transporters are known to be expressed in humans, they could contribute to the low cerebrospinal and seminal fluid antiretroviral concentrations reported in the clinic.
Iron-Induced Virulence of Salmonella enterica Serovar Typhimurium at the Intestinal Epithelial Interface Can Be Suppressed by Carvacrol
Authors: Kortman Guus A. M. , Roelofs Rian W. H. M. , Swinkels Dorine W. , de Jonge Marien I. , Burt Sara A. , Tjalsma Harold 
Published: December 2013

ABSTRACT

Oral iron therapy can increase the abundance of bacterial pathogens, e.g.,
Salmonella
spp., in the large intestine of African children. Carvacrol is a natural compound with antimicrobial activity against various intestinal bacterial pathogens, among which is the highly prevalent
Salmonella enterica
serovar Typhimurium. This study aimed to explore a presumed interaction between carvacrol and bacterial iron handling and to assess the potential of carvacrol in preventing the increase of bacterial pathogenicity during high iron availability.
S
. Typhimurium was cultured with increasing concentrations of iron and carvacrol to study the effects of these combined interventions on growth, adhesion to intestinal epithelial cells, and iron uptake/influx in both bacterial and epithelial cells. In addition, the ability of carvacrol to remove iron from the high-affinity ligand transferrin and an Fe-dye complex was examined. Carvacrol retarded growth of
S
. Typhimurium at all iron conditions. Furthermore, iron-induced epithelial adhesion was effectively reduced by carvacrol at high iron concentrations. The reduction of growth and virulence by carvacrol was not paralleled by a change in iron uptake or influx into
S
. Typhimurium. In contrast, bioavailability of iron for epithelial cells was moderately decreased under these conditions. Further, carvacrol was shown to lack the properties of an iron binding molecule; however, it was able to weaken iron-ligand interactions by which it may possibly interfere with bacterial virulence. In conclusion, our
in vitro
data suggest that carvacrol has the potential to serve as a novel dietary supplement to prevent pathogenic overgrowth and colonization in the large intestine during oral iron therapy.
In Vitro
Activity of Solithromycin against Erythromycin-Resistant Streptococcus agalactiae
Authors: Piccinelli Giorgio , Fernandes Prabhavathi , Bonfanti Carlo , Caccuri Francesca , Caruso Arnaldo , De Francesco Maria Antonia 
Published: December 2013

ABSTRACT

The
in vitro
antibacterial activity of solithromycin (CEM-101) against macrolide-resistant isolates (
n
= 62) of
Streptococcus agalactiae
(group B streptococcus [GBS]) was determined. Phenotypic characterization of macrolide-resistant strains was performed by double-disc diffusion testing. A multiplex PCR was used to identify the
erm
(B),
erm
(TR), and
mef
(A/E) genes, capsular genotypes, and alpha-like (Alp) protein genes from the GBS strains. Determination of MIC was carried out using the microdilution broth method. The Etest method was used for penicillin, azithromycin, clarithromycin, and erythromycin. Solithromycin had a MIC
50
of ≤0.008 μg/ml and a MIC
90
of 0.015 μg/ml against macrolide-susceptible
S. agalactiae
. These MICs were lower than those displayed by penicillin (MIC
50
of 0.032 μg/ml and MIC
90
of 0.047 μg/ml), the antibiotic agent of choice for prophylaxis and treatment of GBS infections. Against macrolide-resistant
S. agalactiae
, solithromycin had a MIC
50
of 0.03 μg/ml and a MIC
90
of 0.125 μg/ml. Against
erm
(B) strains, solithromycin had a MIC
50
of 0.03 μg/ml and a MIC
90
of 0.06 μg/ml, while against
mef
(A) strains, it had a MIC
50
of 0.03 μg/ml and a MIC
90
of 0.125 μg/ml. Most erythromycin-resistant GBS strains were of serotype V (64.5%) and associated significantly with
alp2-3
. Moreover, a statistically significant association was observed between the constitutive macrolide-lincosamide-streptogramin B resistance (cMLS
B
) phenotype and the
erm
(B) gene-carrying strains, the
alp2-3
gene and the M phenotype, and the
mef
(A/E) gene and
epsilon
. Overall, our results show that solithromycin had lower or similar MICs than penicillin and potent activity against macrolide-resistant strains independent of their genotype or phenotype, representing a valid therapeutic alternative where β-lactams cannot be used.
Substituted Diphenyl Ethers as a Novel Chemotherapeutic Platform against Burkholderia pseudomallei
Authors: Cummings Jason E. , Beaupre Adam J. , Knudson Susan E. , Liu Nina , Yu Weixuan , Neckles Carla , Wang Hui , Khanna Avinash , Bommineni Gopal R. , Trunck Lily A. , Schweizer Herbert P. , Tonge Peter J. , Slayden Richard A. 
Published: December 2013

ABSTRACT

Identification of a novel class of anti-
Burkholderia
compounds is key in addressing antimicrobial resistance to current therapies as well as naturally occurring resistance. The FabI enoyl-ACP reductase in
Burkholderia
is an underexploited target that presents an opportunity for development of a new class of inhibitors. A library of substituted diphenyl ethers was used to identify FabI1-specific inhibitors for assessment in
Burkholderia pseudomallei ex vivo
and murine efficacy models. Active FabI1 inhibitors were identified in a two-stage format consisting of percent inhibition screening and MIC determination by the broth microdilution method. Each compound was evaluated against the
B. pseudomallei
1026b (efflux-proficient) and Bp400 (efflux-compromised) strains.
In vitro
screening identified candidate substituted diphenyl ethers that exhibited MICs of less than 1 μg/ml, and enzyme kinetic assays were used to assess potency and specificity against the FabI1 enzyme. These compounds demonstrated activity in a
Burkholderia ex vivo
efficacy model, and two demonstrated efficacy in an acute
B. pseudomallei
mouse infection model. This work establishes substituted diphenyl ethers as a suitable platform for development of novel anti-
Burkholderia
compounds that can be used for treatment of melioidosis.
Disruption of Biofilm Formation by the Human Pathogen Acinetobacter baumannii Using Engineered Quorum-Quenching Lactonases
Authors: Chow Jeng Yeong , Yang Yuanyong , Tay Song Buck , Chua Kim Lee , Yew Wen Shan 
Published: December 2013

ABSTRACT

Acinetobacter baumannii
is a major human pathogen associated with multidrug-resistant nosocomial infections; its virulence is attributed to quorum-sensing-mediated biofilm formation, and disruption of biofilm formation is an attractive antivirulence strategy. Here, we report the first successful demonstration of biofilm disruption in a clinical isolate of
A. baumannii
S1, using a quorum-quenching lactonase obtained by directed evolution; this engineered lactonase significantly reduced the biomass of
A. baumannii
-associated biofilms, demonstrating the utility of this antivirulence strategy.
Antimicrobial Activity of Ceftazidime-Avibactam against Gram-Negative Organisms Collected from U.S. Medical Centers in 2012
Authors: Sader Helio S. , Castanheira Mariana , Flamm Robert K. , Farrell David J. , Jones Ronald N. 
Published: December 2013

ABSTRACT

The activities of the novel β-lactam–β-lactamase inhibitor combination ceftazidime-avibactam and comparator agents were evaluated against a contemporary collection of clinically significant Gram-negative bacilli. Avibactam is a novel non-β-lactam β-lactamase inhibitor that inhibits Ambler class A, C, and some D enzymes. A total of 10,928 Gram-negative bacilli—8,640
Enterobacteriaceae
, 1,967
Pseudomonas aeruginosa
, and 321
Acinetobacter
sp. isolates—were collected from 73 U.S. hospitals and tested for susceptibility by reference broth microdilution methods in a central monitoring laboratory (JMI Laboratories, North Liberty, IA, USA). Ceftazidime was combined with avibactam at a fixed concentration of 4 μg/ml. Overall, 99.8% of
Enterobacteriaceae
strains were inhibited at a ceftazidime-avibactam MIC of ≤4 μg/ml. Ceftazidime-avibactam was active against extended-spectrum β-lactamase (ESBL)-phenotype
Escherichia coli
and
Klebsiella pneumoniae
, meropenem-nonsusceptible (MIC ≥ 2 μg/ml)
K. pneumoniae
, and ceftazidime-nonsusceptible
Enterobacter cloacae
. Among ESBL-phenotype
K. pneumoniae
strains, 61.1% were meropenem susceptible and 99.3% were inhibited at a ceftazidime-avibactam MIC of ≤4 μg/ml. Among
P. aeruginosa
strains, 96.9% were inhibited at a ceftazidime-avibactam MIC of ≤8 μg/ml, and susceptibility rates for meropenem, ceftazidime, and piperacillin-tazobactam were 82.0, 83.2, and 78.3%, respectively. Ceftazidime-avibactam was the most active compound tested against meropenem-nonsusceptible
P. aeruginosa
(MIC
50
/MIC
90
, 4/16 μg/ml; 87.3% inhibited at ≤8 μg/ml).
Acinetobacter
spp. (ceftazidime-avibactam MIC
50
/MIC
90
, 16/>32 μg/ml) showed high rates of resistance to most tested agents. In summary, ceftazidime-avibactam demonstrated potent activity against a large collection of contemporary Gram-negative bacilli isolated from patients in U.S. hospitals in 2012, including organisms that are resistant to most currently available agents, such as
K. pneumoniae
carbapenemase (KPC)-producing
Enterobacteriaceae
and meropenem-nonsusceptible
P. aeruginosa
.
Plasmodium berghei Sporozoites Acquire Virulence and Immunogenicity during Mosquito Hemocoel Transit
Authors: Sato Yuko , Montagna Georgina N. , Matuschewski Kai 
Published: December 2013

ABSTRACT

Malaria is a vector-borne disease caused by the single-cell eukaryote
Plasmodium
. The infectious parasite forms are sporozoites, which originate from midgut-associated oocysts, where they eventually egress and reach the mosquito hemocoel. Sporozoites actively colonize the salivary glands in order to be transmitted to the mammalian host. Whether residence in the salivary glands provides distinct and vital cues for the development of infectivity remains unsolved. In this study, we systematically compared the infectivity of
Plasmodium berghei
sporozoites isolated from the mosquito hemocoel and salivary glands. Hemocoel sporozoites display a lower proportion of gliding motility but develop into liver stages when added to cultured hepatoma cells or after intravenous injection into mice. Mice infected by hemocoel sporozoites had blood infections similar to those induced by sporozoites liberated from salivary glands. These infected mice display indistinguishable systemic inflammatory cytokine responses and develop experimental cerebral malaria. When used as metabolically active, live attenuated vaccine, hemocoel sporozoites elicit substantial protection against sporozoite challenge infections. Collectively, these findings show that salivary gland colonization does not influence parasite virulence in the mammalian host when sporozoites are administered intravenously. This conclusion has important implications for
in vitro
sporozoite production and manufacturing of whole-sporozoite vaccines.
Three Antagonistic Cyclic di-GMP-Catabolizing Enzymes Promote Differential Dot/Icm Effector Delivery and Intracellular Survival at the Early Steps of Legionella pneumophila Infection
Authors: Allombert Julie , Lazzaroni Jean-Claude , Baïlo Nathalie , Gilbert Christophe , Charpentier Xavier , Doublet Patricia , Vianney Anne 
Published: December 2013

ABSTRACT

Legionella pneumophila
is an intracellular pathogen which replicates within protozoan cells and can accidently infect alveolar macrophages, causing an acute pneumonia in humans. The second messenger cyclic di-GMP (c-di-GMP) has been shown to play key roles in the regulation of various bacterial processes, including virulence. While investigating the function of the 22 potential c-di-GMP-metabolizing enzymes of the
L. pneumophila
Lens strain, we found three that directly contribute to its ability to infect both protozoan and mammalian cells. These three enzymes display diguanylate cyclase (Lpl0780), phosphodiesterase (Lpl1118), and bifunctional diguanylate cyclase/phosphodiesterase (Lpl0922) activities, which are all required for the survival and intracellular replication of
L. pneumophila
. Mutants with deletions of the corresponding genes are efficiently taken up by phagocytic cells but are partially defective for the escape of the
Legionella
-containing vacuole (LCV) from the host degradative endocytic pathway and result in lower survival. In addition, Lpl1118 is required for efficient endoplasmic reticulum recruitment to the LCV. Trafficking and biogenesis of the LCV are dependent upon the orchestrated actions of several type 4 secretion system Dot/Icm effectors proteins, which exhibit differentially altered translocation in the three mutants. While translocation of some effectors remained unchanged, others appeared over- and undertranslocated. A general translocation offset of the large repertoire of Dot/Icm effectors may be responsible for the observed defects in the trafficking and biogenesis of the LCV. Our results suggest that
L. pneumophila
uses cyclic di-GMP signaling to fine-tune effector delivery and ensure effective evasion of the host degradative pathways and establishment of a replicative vacuole.
Interleukin-3-Deficient Mice Have Increased Resistance to Blood-Stage Malaria
Authors: Auclair Sarah R. , Roth Kenneth E. , Saunders Bryan L. , Ogborn Kathryn M. , Sheikh Abdalla A. , Naples Julianne , Young Anna Marie P. , Boisen Dorottya K. , Tavangar Amelia T. , Welch Jane E. , Lantz Chris S. 
Published: December 2013

ABSTRACTThe contribution of interleukin-3 (IL-3), a hematopoietic growth factor and immunoregulatory cytokine, to resistance to blood-stage malaria was investigated by infecting IL-3-deficient (knockout [KO]) mice withPlasmodium bergheiNK65. Male IL-3 KO mice, but not female mice, were more resistant to infection than wild-type (WT) mice, as evidenced by lower peak parasitemia and prolonged survival. Both male and female IL-3 KO mice had increased splenomegaly and were more anemic than corresponding WT mice. Anemia was compensated for by an increase in bone marrow and splenic erythropoiesis in IL-3 KO mice, as evidenced by higher levels of erythroid progenitors. Plasma levels of gamma interferon (IFN-γ) and CXCL9 (monokine induced by IFN-γ [MIG]) were found to be significantly reduced in IL-3 KO mice during early stages of infection. In contrast, granulocyte colony-stimulating factor (G-CSF) levels were significantly higher, and the percentage of peripheral blood neutrophils lower, in infected IL-3 KO mice than in WT counterparts. Overall, our results indicate that IL-3 plays a critical role in suppressing protective immunity toP. bergheiNK65 infection and that it is involved in inhibiting the development of splenomegaly, anemia, and erythropoiesis. IL-3 also influences IFN-γ, CXCL9, and G-CSF production in response to infection. The abnormal responses seen in infected IL-3 KO mice may be due to the lack of IL-3 during development, to the lack of IL-3 in the infected mature mice, or to both.