bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Low-Dose Amoxicillin on Staphylococcus aureus USA300 Biofilms
Authors: Mlynek Kevin D. , Callahan Mary T. , Shimkevitch Anton V. , Farmer Jackson T. , Endres Jennifer L. , Marchand Mélodie , Bayles Kenneth W. , Horswill Alexander R. , Kaplan Jeffrey B. 
Published: February 2016

ABSTRACT

Previous studies showed that sub-MIC levels of β-lactam antibiotics stimulate biofilm formation in most methicillin-resistant
Staphylococcus aureus
(MRSA) strains. Here, we investigated this process by measuring the effects of sub-MIC amoxicillin on biofilm formation by the epidemic community-associated MRSA strain USA300. We found that sub-MIC amoxicillin increased the ability of USA300 cells to attach to surfaces and form biofilms under both static and flow conditions. We also found that USA300 biofilms cultured in sub-MIC amoxicillin were thicker, contained more pillar and channel structures, and were less porous than biofilms cultured without antibiotic. Biofilm formation in sub-MIC amoxicillin correlated with the production of extracellular DNA (eDNA). However, eDNA released by amoxicillin-induced cell lysis alone was evidently not sufficient to stimulate biofilm. Sub-MIC levels of two other cell wall-active agents with different mechanisms of action—
d
-cycloserine and fosfomycin—also stimulated eDNA-dependent biofilm, suggesting that biofilm formation may be a mechanistic adaptation to cell wall stress. Screening a USA300 mariner transposon library for mutants deficient in biofilm formation in sub-MIC amoxicillin identified numerous known mediators of
S. aureus
β-lactam resistance and biofilm formation, as well as novel genes not previously associated with these phenotypes. Our results link cell wall stress and biofilm formation in MRSA and suggest that eDNA-dependent biofilm formation by strain USA300 in low-dose amoxicillin is an inducible phenotype that can be used to identify novel genes impacting MRSA β-lactam resistance and biofilm formation.
Low Concentrations of Nitric Oxide Modulate Streptococcus pneumoniae Biofilm Metabolism and Antibiotic Tolerance
Authors: Allan Raymond N. , Morgan Samantha , Brito-Mutunayagam Sanjita , Skipp Paul , Feelisch Martin , Hayes Stephen M. , Hellier William , Clarke Stuart C. , Stoodley Paul , Burgess Andrea , Ismail-Koch Hasnaa , Salib Rami J. , Webb Jeremy S. , Faust Saul N. , Hall-Stoodley Luanne 
Published: February 2016

ABSTRACT

Streptococcus pneumoniae
is one of the key pathogens responsible for otitis media (OM), the most common infection in children and the largest cause of childhood antibiotic prescription. Novel therapeutic strategies that reduce the overall antibiotic consumption due to OM are required because, although widespread pneumococcal conjugate immunization has controlled invasive pneumococcal disease, overall OM incidence has not decreased. Biofilm formation represents an important phenotype contributing to the antibiotic tolerance and persistence of
S. pneumoniae
in chronic or recurrent OM. We investigated the treatment of pneumococcal biofilms with nitric oxide (NO), an endogenous signaling molecule and therapeutic agent that has been demonstrated to trigger biofilm dispersal in other bacterial species. We hypothesized that addition of low concentrations of NO to pneumococcal biofilms would improve antibiotic efficacy and that higher concentrations exert direct antibacterial effects. Unlike in many other bacterial species, low concentrations of NO did not result in
S. pneumoniae
biofilm dispersal. Instead, treatment of both
in vitro
biofilms and
ex vivo
adenoid tissue samples (a reservoir for
S. pneumoniae
biofilms) with low concentrations of NO enhanced pneumococcal killing when combined with amoxicillin-clavulanic acid, an antibiotic commonly used to treat chronic OM. Quantitative proteomic analysis using iTRAQ (isobaric tag for relative and absolute quantitation) identified 13 proteins that were differentially expressed following low-concentration NO treatment, 85% of which function in metabolism or translation. Treatment with low-concentration NO, therefore, appears to modulate pneumococcal metabolism and may represent a novel therapeutic approach to reduce antibiotic tolerance in pneumococcal biofilms.
Association of Novel Nonsynonymous Single Nucleotide Polymorphisms inampDwith Cephalosporin Resistance and Phylogenetic Variations inampC,ampR,ompF, andompCin Enterobacter cloacae Isolates That Are Highly Resistant to Carbapenems
Authors: Babouee Flury Baharak , Ellington Matthew J. , Hopkins Katie L. , Turton Jane F. , Doumith Michel , Loy Richard , Staves Peter , Hinic Vladimira , Frei Reno , Woodford Neil 
Published: February 2016

ABSTRACTInEnterobacter cloacae, the genetic lesions associated with derepression of the AmpC β-lactamase include diverse single nucleotide polymorphisms (SNPs) and/or indels in theampDandampRgenes and SNPs inampC, while diverse SNPs in the promoter region or SNPs/indels within the coding sequence of outer membrane proteins have been described to alter porin production leading to carbapenem resistance. We sought to define the underlying mechanisms conferring cephalosporin and carbapenem resistance in a collection ofE. cloacaeisolates with unusually high carbapenem resistance and no known carbapenemase and, in contrast to many previous studies, considered the SNPs we detected in relation to the multilocus sequence type (MLST)-based phylogeny of our collection. Whole-genome sequencing was applied on the most resistant isolates to seek novel carbapenemases, expression ofampCwas measured by reverse transcriptase PCR, and porin translation was detected by SDS-PAGE. SNPs occurring inampC,ampR,ompF, andompCgenes (and their promoter regions) were mostly phylogenetic variations, relating to the isolates' sequence types, whereas nonsynonymous SNPs inampDwere associated with derepression of AmpC and cephalosporin resistance. The additional loss of porins resulted in high-level carbapenem resistance, underlining the clinical importance of chromosomal mutations among carbapenem-resistantE. cloacae.
Landscape of Resistance-Nodulation-Cell Division (RND)-Type Efflux Pumps in Enterobacter cloacae Complex
Authors: Guérin François , Lallement Claire , Isnard Christophe , Dhalluin Anne , Cattoir Vincent , Giard Jean-Christophe 
Published: February 2016

ABSTRACT

In Gram-negative bacteria, the active efflux is an important mechanism of antimicrobial resistance, but little is known about the
Enterobacter cloacae
complex (ECC). It is mediated primarily by pumps belonging to the RND (resistance-nodulation-cell division) family, and only AcrB, part of the AcrAB-TolC tripartite system, was characterized in ECC. However, detailed genome sequence analysis of the strain
E. cloacae
subsp.
cloacae
ATCC 13047 revealed to us that 10 other genes putatively coded for RND-type transporters. We then characterized the role of all of these candidates by construction of corresponding deletion mutants, which were tested for their antimicrobial susceptibility to 36 compounds, their virulence in the invertebrate
Galleria mellonella
model of infection, and their ability to form biofilm. Only the Δ
acrB
mutant displayed significantly different phenotypes compared to that of the wild-type strain: 4- to 32-fold decrease of MICs of several antibiotics, antiseptics, and dyes, increased production of biofilm, and attenuated virulence in
G. mellonella
. In order to identify specific substrates of each pump, we individually expressed in
trans
all operons containing an RND pump-encoding gene into the Δ
acrB
hypersusceptible strain. We showed that three other RND-type efflux systems (ECL_00053-00055, ECL_01758-01759, and ECL_02124-02125) were able to partially restore the wild-type phenotype and to superadd to and even enlarge the broad range of antimicrobial resistance. This is the first global study assessing the role of all RND efflux pumps chromosomally encoded by the ECC, which confirms the major role of AcrB in both pathogenicity and resistance and the potential involvement of other RND-type members in acquired resistance.
Rapid Emergence and Evolution of Staphylococcus aureus Clones Harboring
fusC
-Containing Staphylococcal Cassette Chromosome Elements
Authors: Baines Sarah L. , Howden Benjamin P. , Heffernan Helen , Stinear Timothy P. , Carter Glen P. , Seemann Torsten , Kwong Jason C. , Ritchie Stephen R. , Williamson Deborah A. 
Published: February 2016

ABSTRACT

The prevalence of fusidic acid (FA) resistance among
Staphylococcus aureus
strains in New Zealand (NZ) is among the highest reported globally, with a recent study describing a resistance rate of approximately 28%. Three FA-resistant
S. aureus
clones (ST5 MRSA, ST1 MSSA, and ST1 MRSA) have emerged over the past decade and now predominate in NZ, and in all three clones FA resistance is mediated by the
fusC
gene. In particular, ST5 MRSA has rapidly become the dominant MRSA clone in NZ, although the origin of FA-resistant ST5 MRSA has not been explored, and the genetic context of
fusC
in FA-resistant NZ isolates is unknown. To better understand the rapid emergence of FA-resistant
S. aureus
, we used population-based comparative genomics to characterize a collection of FA-resistant and FA-susceptible isolates from NZ. FA-resistant NZ ST5 MRSA displayed minimal genetic diversity and represented a phylogenetically distinct clade within a global population model of clonal complex 5 (CC5)
S. aureus
. In all lineages,
fusC
was invariably located within staphylococcal cassette chromosome (SCC) elements, suggesting that SCC-mediated horizontal transfer is the primary mechanism of
fusC
dissemination. The genotypic association of
fusC
with
mecA
has important implications for the emergence of MRSA clones in populations with high usage of fusidic acid. In addition, we found that
fusC
was colocated with a recently described virulence factor (
tirS
) in dominant NZ
S. aureus
clones, suggesting a fitness advantage. This study points to the likely molecular mechanisms responsible for the successful emergence and spread of FA-resistant
S. aureus
.
Derivation and Multicenter Validation of the Drug Resistance in Pneumonia Clinical Prediction Score
Authors: Webb Brandon J. , Dascomb Kristin , Stenehjem Edward , Vikram Holenarasipur R. , Agrwal Neera , Sakata Kenneth , Williams Kathryn , Bockorny Bruno , Bagavathy Kavitha , Mirza Shireen , Metersky Mark , Dean Nathan C. 
Published: February 2016

ABSTRACT

The health care-associated pneumonia (HCAP) criteria have a limited ability to predict pneumonia caused by drug-resistant bacteria and favor the overutilization of broad-spectrum antibiotics. We aimed to derive and validate a clinical prediction score with an improved ability to predict the risk of pneumonia due to drug-resistant pathogens compared to that of HCAP criteria. A derivation cohort of 200 microbiologically confirmed pneumonia cases in 2011 and 2012 was identified retrospectively. Risk factors for pneumonia due to drug-resistant pathogens were evaluated by logistic regression, and a novel prediction score (the drug resistance in pneumonia [DRIP] score) was derived. The score was then validated in a prospective, observational cohort of 200 microbiologically confirmed cases of pneumonia at four U.S. centers in 2013 and 2014. The DRIP score (area under the receiver operator curve [AUROC], 0.88 [95% confidence interval {CI}, 0.82 to 0.93]) performed significantly better (
P
= 0.02) than the HCAP criteria (AUROC, 0.72 [95% CI, 0.64 to 0.79]). At a threshold of ≥4 points, the DRIP score demonstrated a sensitivity of 0.82 (95% CI, 0.67 to 0.88), a specificity of 0.81 (95% CI, 0.73 to 0.87), a positive predictive value (PPV) of 0.68 (95% CI, 0.56 to 0.78), and a negative predictive value (NPV) of 0.90 (95% CI, 0.81 to 0.93). By comparison, the performance of HCAP criteria was less favorable: sensitivity was 0.79 (95% CI, 0.67 to 0.88), specificity was 0.65 (95% CI, 0.56 to 0.73), PPV was 0.53 (95% CI, 0.42 to 0.63), and NPV was 0.86 (95% CI, 0.77 to 0.92). The overall accuracy of the HCAP criteria was 69.5% (95% CI, 62.5 to 75.7%), whereas that of the DRIP score was 81.5% (95% CI, 74.2 to 85.6%) (
P
= 0.005). Unnecessary extended-spectrum antibiotics were recommended 46% less frequently by applying the DRIP score (25/200, 12.5%) than by use of HCAP criteria (47/200, 23.5%) (
P
= 0.004), without increasing the rate at which inadequate treatment recommendations were made. The DRIP score was more predictive of the risk of pneumonia due to drug-resistant pathogens than HCAP criteria and may have the potential to decrease antibiotic overutilization in patients with pneumonia. Validation in larger cohorts of patients with pneumonia due to all causes is necessary.
Optimizing the Clinical Use of Vancomycin
Authors: Álvarez Rocío , López Cortés Luis E. , Molina José , Cisneros José M. , Pachón Jerónimo 
Published: February 2016

ABSTRACT

The increasing number of infections produced by beta-lactam–resistant Gram-positive bacteria and the morbidity secondary to these infections make it necessary to optimize the use of vancomycin. In 2009, the American Society of Health-System Pharmacists, the Infectious Diseases Society of America, and the Society of Infectious Disease Pharmacists published specific guidelines about vancomycin dosage and monitoring. However, these guidelines have not been updated in the past 6 years. This review analyzes the new available information about vancomycin published in recent years regarding pharmacokinetics and pharmacodynamics, serum concentration monitoring, and optimal vancomycin dosing in special situations (obese people, burn patients, renal replacement therapy, among others). Vancomycin efficacy is linked to a correct dosage which should aim to reach an area under the curve (AUC)/MIC ratio of ≥400; serum trough levels of 15 to 20 mg/liter are considered a surrogate marker of an AUC/MIC ratio of ≥400 for a MIC of ≤1 mg/liter. For
Staphylococcus aureus
strains presenting with a MIC >1 mg/liter, an alternative agent should be considered. Vancomycin doses must be adjusted according to body weight and the plasma trough levels of the drug. Nephrotoxicity has been associated with target vancomycin trough levels above 15 mg/liter. Continuous infusion is an option, especially for patients at high risk of renal impairment or unstable vancomycin clearance. In such cases, vancomycin plasma steady-state level and creatinine monitoring are strongly indicated.
Card9- and MyD88-Mediated Gamma Interferon and Nitric Oxide Production Is Essential for Resistance to Subcutaneous Coccidioides posadasii Infection
Authors: Hung Chiung-Yu , Castro-Lopez Natalia , Cole Garry T. 
Published: February 2016

ABSTRACT

Coccidioidomycosis is a potentially life-threatening respiratory disease which is endemic to the southwestern United States and arid regions of Central and South America. It is responsible for approximately 150,000 infections annually in the United States alone. Almost every human organ has been reported to harbor parasitic cells of
Coccidioides
spp. in collective cases of the disseminated form of this mycosis. Current understanding of the mechanisms of protective immunity against lung infection has been largely derived from murine models of pulmonary coccidioidomycosis. However, little is known about the nature of the host response to
Coccidioides
in extrapulmonary tissue. Primary subcutaneous coccidioidal infection is rare but has been reported to result in disseminated disease. Here, we show that activation of MyD88 and Card9 signal pathways are required for resistance to
Coccidioides
infection following subcutaneous challenge of C57BL/6 mice, which correlates with earlier findings of the protective response to pulmonary infection.
MyD88
−/−
and
Card9
−/−
mice recruited reduced numbers of T cells, B cells, and neutrophils to the
Coccidioides
-infected hypodermis compared to wild-type mice; however, neutrophils were dispensable for resistance to skin infection. Further studies have shown that gamma interferon (IFN-γ) production and activation of Th1 cells characterize resistance to subcutaneous infection. Furthermore, activation of a phagosomal enzyme, inducible nitric oxide synthase, which is necessary for NO production, is a requisite for fungal clearance in the hypodermis. Collectively, our data demonstrate that MyD88- and Card9-mediated IFN-γ and nitric oxide production is essential for protection against subcutaneous
Coccidioides
infection.
Local Generation of Kynurenines Mediates Inhibition of Neutrophil Chemotaxis by Uropathogenic Escherichia coli
Authors: Loughman Jennifer A. , Yarbrough Melanie L. , Tiemann Kristin M. , Hunstad David A. 
Published: February 2016

ABSTRACT

During epithelial infections, pathogenic bacteria employ an array of strategies to attenuate and evade host immune responses, including the influx of polymorphonuclear leukocytes (PMN; neutrophils). Among the most common bacterial infections in humans are those of the urinary tract, caused chiefly by uropathogenic
Escherichia coli
(UPEC). During the establishment of bacterial cystitis, UPEC suppresses innate responses via multiple independent strategies. We recently described UPEC attenuation of PMN trafficking to the urinary bladder through pathogen-specific local induction of indoleamine 2,3-dioxygenase (IDO), a tryptophan catabolic enzyme previously shown to have regulatory activity only in adaptive immunity. Here, we investigated the mechanism by which IDO induction attenuates PMN migration. Local tryptophan limitation, by which IDO is known to influence T cell longevity and proliferation, was not involved in its effect on PMN trafficking. Instead, metabolites in the IDO pathway, particularly
l
-kynurenine, directly suppressed PMN transepithelial migration and induced an attached, spread morphology in PMN both at rest and in the presence of chemotactic stimuli. Finally, kynurenines represent known ligands of the mammalian aryl hydrocarbon receptor (AHR), and UPEC infection of
Ahr
−/−
mice recapitulated the derepressed PMN recruitment observed previously in
Ido1
−/−
mice. UPEC therefore suppresses neutrophil migration early in bacterial cystitis by eliciting an IDO-mediated increase in local production of kynurenines, which act through the AHR to impair neutrophil chemotaxis.
Galectin-3 Plays an Important Role in Innate Immunity to Gastric Infection by Helicobacter pylori
Authors: Park Ah-Mee , Hagiwara Satoru , Hsu Daniel K. , Liu Fu-Tong , Yoshie Osamu 
Published: February 2016

ABSTRACT

We studied the role of galectin-3 (Gal3) in gastric infection by
Helicobacter pylori
. We first demonstrated that Gal3 was selectively expressed by gastric surface epithelial cells and abundantly secreted into the surface mucus layer. We next inoculated
H. pylori
Sydney strain 1 into wild-type (WT) and Gal3-deficient mice using a stomach tube. At 2 weeks postinoculation, the bacterial cells were mostly trapped within the surface mucus layer in WT mice. In sharp contrast, they infiltrated deep into the gastric glands in Gal3-deficient mice. Bacterial loads in the gastric tissues were also much higher in Gal3-deficient mice than in WT mice. At 6 months postinoculation,
H. pylori
had successfully colonized within the gastric glands of both WT and Gal3-deficient mice, although the bacterial loads were still higher in the latter. Furthermore, large lymphoid clusters mostly consisting of B cells were frequently observed in the gastric submucosa of Gal3-deficient mice.
In vitro
, peritoneal macrophages from Gal3-deficient mice were inefficient in killing engulfed
H. pylori
. Furthermore, recombinant Gal3 not only induced rapid aggregation of
H. pylori
but also exerted a potent bactericidal effect on
H. pylori
as revealed by propidium iodide uptake and a morphological shift from spiral to coccoid form. However, a minor fraction of bacterial cells, probably transient phase variants of Gal3-binding sugar moieties, escaped killing by Gal3. Collectively, our data demonstrate that Gal3 plays an important role in innate immunity to infection and colonization of
H. pylori
.
Porphyromonas gingivalis Outer Membrane Vesicles Induce Selective Tumor Necrosis Factor Tolerance in a Toll-Like Receptor 4- and mTOR-Dependent Manner
Authors: Waller Tobias , Kesper Laura , Hirschfeld Josefine , Dommisch Henrik , Kölpin Johanna , Oldenburg Johannes , Uebele Julia , Hoerauf Achim , Deschner James , Jepsen Sören , Bekeredjian-Ding Isabelle 
Published: February 2016

ABSTRACT

Porphyromonas gingivalis
is an important member of the anaerobic oral flora. Its presence fosters growth of periodontal biofilm and development of periodontitis. In this study, we demonstrated that lipophilic outer membrane vesicles (OMV) shed from
P. gingivalis
promote monocyte unresponsiveness to live
P. gingivalis
but retain reactivity to stimulation with bacterial DNA isolated from
P. gingivalis
or AIM2 ligand poly(dA·dT). OMV-mediated tolerance of
P. gingivalis
is characterized by selective abrogation of tumor necrosis factor (TNF). Neutralization of interleukin-10 (IL-10) during OMV challenge partially restores monocyte responsiveness to
P. gingivalis
; full reactivity to
P. gingivalis
can be restored by inhibition of mTOR signaling, which we previously identified as the major signaling pathway promoting Toll-like receptor 2 and Toll-like receptor 4 (TLR2/4)-mediated tolerance in monocytes. However, despite previous reports emphasizing a central role of TLR2 in innate immune recognition of
P. gingivalis
, our current findings highlight a selective role of TLR4 in the promotion of OMV-mediated TNF tolerance: only blockade of TLR4—and not of TLR2—restores responsiveness to
P. gingivalis
. Of further note, OMV-mediated tolerance is preserved in the presence of cytochalasin B and chloroquine, indicating that triggering of surface TLR4 is sufficient for this effect. Taking the results together, we propose that
P. gingivalis
OMV contribute to local immune evasion of
P. gingivalis
by hampering the host response.
Dietary Omega-3 Fatty Acids Increase Survival and Decrease Bacterial Load in Mice Subjected to Staphylococcus aureus-Induced Sepsis
Authors: Svahn Sara L. , Ulleryd Marcus A. , Grahnemo Louise , Ståhlman Marcus , Borén Jan , Nilsson Staffan , Jansson John-Olov , Johansson Maria E. 
Published: February 2016

ABSTRACT

Sepsis caused by
Staphylococcus aureus
is increasing in incidence. With the alarming use of antibiotics,
S. aureus
is prone to become methicillin resistant. Antibiotics are the only widely used pharmacological treatment for sepsis. Interestingly, mice fed high-fat diet (HFD) rich in polyunsaturated fatty acids have better survival of
S. aureus
-induced sepsis than mice fed HFD rich in saturated fatty acids (HFD-S). To investigate what component of polyunsaturated fatty acids, i.e., omega-3 or omega-6 fatty acids, exerts beneficial effects on the survival of
S. aureus
-induced sepsis, mice were fed HFD rich in omega-3 or omega-6 fatty acids for 8 weeks prior to inoculation with
S. aureus
. Further, mice fed HFD-S were treated with omega-3 fatty acid metabolites known as resolvins. Mice fed HFD rich in omega-3 fatty acids had increased survival and decreased bacterial loads compared to those for mice fed HFD-S after
S. aureus
-induced sepsis. Furthermore, the bacterial load was decreased in resolvin-treated mice fed HFD-S after
S. aureus
-induced sepsis compared with that in mice treated with vehicle. Dietary omega-3 fatty acids increase the survival of
S. aureus
-induced sepsis by reversing the deleterious effect of HFD-S on mouse survival.