bluuebunny/crossref_metadata_2025_split huggingface dataset:
Loss of Hypermucoviscosity and Increased Fitness Cost in Colistin-Resistant Klebsiella pneumoniae Sequence Type 23 Strains
Authors: Choi Myung-Jin , Ko Kwan Soo 
Published: August 2015

ABSTRACT

In this study, we investigated the effects of colistin resistance on virulence and fitness in hypermucoviscous (HV)
Klebsiella pneumoniae
sequence type 23 (ST23) strains. Colistin-resistant mutants were developed from three colistin-susceptible HV
K. pneumoniae
ST23 strains. The lipid A structures of strains were analyzed by matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry. Changes in HV were investigated using the string test, and extracellular polysaccharide production was quantified. The expression levels of the
phoQ
,
pmrD
,
pmrB
,
pbgP
,
magA
, and p-
rmpA2
genes, serum resistance, and biofilm-forming activity were determined. The fitness of colistin-resistant mutants compared to that of the parental strains was examined by determining the competitive index (CI). The colistin-resistant mutants exhibited reduced HV, which was accompanied by decreased formation of capsular polysaccharides (CPS) and reduced expression of genes (
magA
and p-
rmpA2
). While there was enhanced expression of
pmrD
and
pbgP
in all colistin-resistant derivatives, there were differences in the expression levels of
phoQ
and
pmrB
between strains. MALDI-TOF analysis detected the addition of aminoarabinose or palmitate to the lipid A moiety of lipopolysaccharide in the colistin-resistant derivatives. In addition, survival rates in the presence of normal human serum were decreased in the mutant strains, and CI values (0.01 to 0.19) indicated significant fitness defects in the colistin-resistant derivatives compared to the respective parental strains. In hypervirulent HV
K. pneumoniae
strains, the acquisition of colistin resistance was accompanied by reduced CPS production, impaired virulence, and a significant fitness cost.
Optimizing the Initial Amikacin Dosage in Adults
Authors: White Bryan P. , Lomaestro Ben , Pai Manjunath P. 
Published: August 2015

ABSTRACT

We report on the pharmacokinetics (PK) and pharmacodynamics (PD) of high-dose (>15 mg/kg of body weight per day) amikacin. A mean (standard deviation [SD]) maximum drug concentration in the serum (
C
max
) and 24-h area under the concentration-time curve (AUC
24
) of 101 (49.4) mg/liter and 600 (387) mg · h/liter, respectively, were observed (
n
= 73) with 28.0 (8.47) mg/kg/day doses. An initial amikacin dose of 2,500 mg in adults weighing 40 kg to 200 kg with therapeutic drug monitoring to adjust the maintenance dose will optimize its PK and PD.
Effects of Selection Pressure and Genetic Association on the Relationship between Antibiotic Resistance and Virulence in Escherichia coli
Authors: Zhang Lixin , Levy Karen , Trueba Gabriel , Cevallos William , Trostle James , Foxman Betsy , Marrs Carl F. , Eisenberg Joseph N. S. 
Published: August 2015

ABSTRACT

Antibiotic selection pressure and genetic associations may lead to the cooccurrence of resistance and virulence in individual pathogens. However, there is a lack of rigorous epidemiological evidence that demonstrates the cooccurrence of resistance and virulence at the population level. Using samples from a population-based case-control study in 25 villages in rural Ecuador, we characterized resistance to 12 antibiotics among pathogenic (
n
= 86) and commensal (
n
= 761)
Escherichia coli
isolates, classified by the presence or absence of known diarrheagenic virulence factor genes. The prevalences of resistance to single and multiple antibiotics were significantly higher for pathogenic isolates than for commensal isolates. Using a generalized estimating equation, antibiotic resistance was independently associated with virulence factor carriage, case status, and antibiotic use (for these respective factors: odds ratio [OR] = 3.0, with a 95% confidence interval [CI] of 1.7 to 5.1; OR = 2.0, with a 95% CI of 1.3 to 3.0; and OR = 1.5, with a 95% CI of 0.9 to 2.5). Virulence factor carriage was more strongly related to antibiotic resistance than antibiotic use for all antibiotics examined, with the exception of fluoroquinolones, gentamicin, and cefotaxime. This study provides epidemiological evidence that antibiotic resistance and virulence factor carriage are linked in
E. coli
populations in a community setting. Further, these data suggest that while the cooccurrence of resistance and virulence in
E. coli
is partially due to antibiotic selection pressure, it is also genetically determined. These findings should be considered in developing strategies for treating infections and controlling for antibiotic resistance.
Hepatitis C Virus Genotype 4 Resistance and Subtype Demographic Characterization of Patients Treated with Ombitasvir plus Paritaprevir/Ritonavir
Authors: Schnell Gretja , Tripathi Rakesh , Beyer Jill , Reisch Thomas , Krishnan Preethi , Lu Liangjun , Dekhtyar Tatyana , Hall Coleen , Vilchez Regis A. , Pilot-Matias Tami , Collins Christine 
Published: August 2015

ABSTRACT
Hepatitis C virus (HCV) genotype 4 (GT4) is genetically diverse, with 17 confirmed subtypes, and comprises approximately 13% of infections worldwide. In this study, we identified GT4 subtypes by phylogenetic analysis, assessed differences in patient demographics across GT4 subtypes, examined baseline sequence variability among subtypes and the potential impact on treatment outcome, and analyzed the development of viral resistance in patients who received a regimen of ombitasvir (nonstructural protein 5A [NS5A] inhibitor) plus ritonavir-boosted paritaprevir (NS3/4A inhibitor) with or without ribavirin (RBV) for the treatment of HCV GT4 infection. Phylogenetic analysis of HCV NS3/4A, NS5A, and NS5B nucleotide sequences identified 7 subtypes (4a, 4b, 4c, 4d, 4f, 4g/4k, and 4o) among 132 patient samples. Subtype prevalence varied by country, and the distributions of patient birth cohort and race were significantly different across GT4 subtypes 4a, 4d, and non-4a/4d. Baseline amino acid variability was detected in NS5A across GT4 subtypes but had no impact on treatment outcome. Three patients experienced virologic failure and were infected with subtype 4d, and the predominant resistance-associated variants at the time of failure were D168V in NS3 and L28V in NS5A. Overall, high response rates were observed among patients infected with 7 HCV GT4 subtypes, with no impact of baseline variants on treatment outcome. GT4 subtype distribution in this study differed based on patient demographics and geography.
Viable but Nonculturable and Persister Cells Coexist Stochastically and Are Induced by Human Serum
Authors: Ayrapetyan M. , Williams T. C. , Baxter R. , Oliver J. D. 
Published: August 2015

ABSTRACT
Dormancy holds a vital role in the ecological dynamics of microorganisms. Specifically, entry into dormancy allows cells to withstand times of stress while maintaining the potential for reentry into an active existence. The viable but nonculturable (VBNC) state and antibiotic persistence are two well-recognized conditions of dormancy demonstrated to contribute to bacterial stress tolerance and, as a consequence, yield populations that are tolerant to high-dose antibiotics. Aside from this commonality, more evidence is being presented that indicates the relatedness of these two states. Here, we demonstrate that VBNC cells are present during persister isolation experiments, further indicating that these cells coexist and are induced by the same conditions. Interestingly, we reveal that VBNC cells can exist stochastically in unstressed growing cultures, a finding that is characteristic of persisters. Furthermore, human serum induces the formation of both VBNC cells and persisters, a finding not previously described for either dormancy state. Lastly, we describe the role of toxin-antitoxin systems (TAS) in the induction of the VBNC state and report that these TAS, which are classically implicated in persister cell formation, are also induced during incubation in human serum. This study provides evidence for the recently proposed “dormancy continuum hypothesis” and substantiates the physical and molecular relatedness of VBNC and persister cells in a standardized model organism. Notably, these results provide new evidence for the clinical significance of VBNC and persister cells.
Plasmodium falciparum Gametocyte-Specific Antibody Profiling Reveals Boosting through Natural Infection and Identifies Potential Markers of Gametocyte Exposure
Authors: Skinner Jeff , Huang Chiung-Yu , Waisberg Michael , Felgner Philip L. , Doumbo Ogobara K. , Ongoiba Aissata , Kayentao Kassoum , Traore Boubacar , Crompton Peter D. , Williamson Kim C. 
Published: August 2015

ABSTRACTMalaria elimination efforts would benefit from vaccines that block transmission ofPlasmodium falciparumgametocytes from humans to mosquitoes. A clear understanding of gametocyte-specific antibody responses in exposed populations could help determine whether transmission-blocking vaccines (TBV) would be boosted by natural gametocyte exposure, and also inform the development of serologic tools to monitor gametocyte exposure in populations targeted for malaria elimination. To this end, plasma was collected from Malian children and adults before and after the 6-month malaria season and probed against a microarray containing 1,204P. falciparumproteins. Using publicly available proteomic data, we classified 91 proteins as gametocyte specific and 69 as proteins not expressed by gametocytes. The overall breadth and magnitude of gametocyte-specific IgG responses increased during the malaria season, although they were consistently lower than IgG responses to nongametocyte antigens. Notably, IgG specific for the TBV candidates Pfs48/45 and Pfs230 increased during the malaria season. In addition, IgGs specific for the gametocyte proteins Pfmdv1, Pfs16, PF3D7_1346400, and PF3D7_1024800 were detected in nearly all subjects, suggesting that seroconversion to these proteins may be a sensitive indicator of gametocyte exposure, although further studies are needed to determine the specificity and kinetics of these potential serologic markers. These findings suggest that TBV-induced immunity would be boosted through natural gametocyte exposure, and that antibody responses to particular antigens may reliably indicate gametocyte exposure.
Surface Glycopolymers Are Crucial for
In Vitro
Anti-Wall Teichoic Acid IgG-Mediated Complement Activation and Opsonophagocytosis of Staphylococcus aureus
Authors: Lee Jong-Ho , Kim Na-Hyang , Winstel Volker , Kurokawa Kenji , Larsen Jesper , An Jang-Hyun , Khan Adnan , Seong Min-Young , Lee Min Ja , Andersen Paal Skytt , Peschel Andreas , Lee Bok Luel 
Published: August 2015

ABSTRACT

The cell envelopes of many Gram-positive bacteria contain wall teichoic acids (WTAs).
Staphylococcus aureus
WTAs are composed of ribitol phosphate (RboP) or glycerol phosphate (GroP) backbones substituted with
d
-alanine and
N
-acetyl-
d
-glucosamine (GlcNAc) or
N
-acetyl-
d
-galactosamine (GalNAc). Two WTA glycosyltransferases, TarM and TarS, are responsible for modifying the RboP WTA with α-GlcNAc and β-GlcNAc, respectively. We recently reported that purified human serum anti-WTA IgG specifically recognizes β-GlcNAc of the staphylococcal RboP WTA and then facilitates complement C3 deposition and opsonophagocytosis of
S. aureus
laboratory strains. This prompted us to examine whether anti-WTA IgG can induce C3 deposition on a diverse set of clinical
S. aureus
isolates. To this end, we compared anti-WTA IgG-mediated C3 deposition and opsonophagocytosis abilities using 13 different staphylococcal strains. Of note, the majority of
S. aureus
strains tested was recognized by anti-WTA IgG, resulting in C3 deposition and opsonophagocytosis. A minority of strains was not recognized by anti-WTA IgG, which correlated with either extensive capsule production or an alteration in the WTA glycosylation pattern. Our results demonstrate that the presence of WTAs with TarS-mediated glycosylation with β-GlcNAc in clinically isolated
S. aureus
strains is an important factor for induction of anti-WTA IgG-mediated C3 deposition and opsonophagocytosis.
Regulation of Nitrite Stress Response in Desulfovibrio vulgaris Hildenborough, a Model Sulfate-Reducing Bacterium
Authors: Rajeev Lara , Chen Amy , Kazakov Alexey E. , Luning Eric G. , Zane Grant M. , Novichkov Pavel S. , Wall Judy D. , Mukhopadhyay Aindrila 
Published: August 2015

ABSTRACT

Sulfate-reducing bacteria (SRB) are sensitive to low concentrations of nitrite, and nitrite has been used to control SRB-related biofouling in oil fields.
Desulfovibrio vulgaris
Hildenborough, a model SRB, carries a cytochrome
c
-type nitrite reductase (
nrfHA
) that confers resistance to low concentrations of nitrite. The regulation of this nitrite reductase has not been directly examined to date. In this study, we show that DVU0621 (NrfR), a sigma54-dependent two-component system response regulator, is the positive regulator for this operon. NrfR activates the expression of the
nrfHA
operon in response to nitrite stress. We also show that
nrfR
is needed for fitness at low cell densities in the presence of nitrite because inactivation of
nrfR
affects the rate of nitrite reduction. We also predict and validate the binding sites for NrfR upstream of the
nrfHA
operon using purified NrfR in gel shift assays. We discuss possible roles for NrfR in regulating nitrate reductase genes in nitrate-utilizing
Desulfovibrio
spp.

IMPORTANCE
The NrfA nitrite reductase is prevalent across several bacterial phyla and required for dissimilatory nitrite reduction. However, regulation of the
nrfA
gene has been studied in only a few nitrate-utilizing bacteria. Here, we show that in
D. vulgaris
, a bacterium that does not respire nitrate, the expression of
nrfHA
is induced by NrfR upon nitrite stress. This is the first report of regulation of
nrfA
by a sigma54-dependent two-component system. Our study increases our knowledge of nitrite stress responses and possibly of the regulation of nitrate reduction in SRB.
A Cardiolipin-Deficient Mutant of Rhodobacter sphaeroides Has an Altered Cell Shape and Is Impaired in Biofilm Formation
Authors: Lin Ti-Yu , Santos Thiago M. A. , Kontur Wayne S. , Donohue Timothy J. , Weibel Douglas B. 
Published: August 2015

ABSTRACT

Cell shape has been suggested to play an important role in the regulation of bacterial attachment to surfaces and the formation of communities associated with surfaces. We found that a cardiolipin synthase (Δ
cls
) mutant of the rod-shaped bacterium
Rhodobacter sphaeroides
—in which synthesis of the anionic, highly curved phospholipid cardiolipin (CL) is reduced by 90%—produces ellipsoid-shaped cells that are impaired in biofilm formation. Reducing the concentration of CL did not cause significant defects in
R. sphaeroides
cell growth, swimming motility, lipopolysaccharide and exopolysaccharide production, surface adhesion protein expression, and membrane permeability. Complementation of the CL-deficient mutant by ectopically expressing CL synthase restored cells to their rod shape and increased biofilm formation. Treating
R. sphaeroides
cells with a low concentration (10 μg/ml) of the small-molecule MreB inhibitor
S
-(3,4-dichlorobenzyl)isothiourea produced ellipsoid-shaped cells that had no obvious growth defect yet reduced
R. sphaeroides
biofilm formation. This study demonstrates that CL plays a role in
R. sphaeroides
cell shape determination, biofilm formation, and the ability of the bacterium to adapt to its environment.

IMPORTANCE
Membrane composition plays a fundamental role in the adaptation of many bacteria to environmental stress. In this study, we build a new connection between the anionic phospholipid cardiolipin (CL) and cellular adaptation in
Rhodobacter sphaeroides
. We demonstrate that CL plays a role in the regulation of
R. sphaeroides
morphology and is important for the ability of this bacterium to form biofilms. This study correlates CL concentration, cell shape, and biofilm formation and provides the first example of how membrane composition in bacteria alters cell morphology and influences adaptation. This study also provides insight into the potential of phospholipid biosynthesis as a target for new chemical strategies designed to alter or prevent biofilm formation.
Whole-Genome Comparison Uncovers Genomic Mutations between Group B Streptococci Sampled from Infected Newborns and Their Mothers
Authors: Almeida Alexandre , Villain Adrien , Joubrel Caroline , Touak Gérald , Sauvage Elisabeth , Rosinski-Chupin Isabelle , Poyart Claire , Glaser Philippe 
Published: August 2015

ABSTRACT

Streptococcus agalactiae
(group B
Streptococcus
or GBS), a commensal of the human gut and genitourinary tract, is a leading cause of neonatal infections, in which vertical transmission from mother to child remains the most frequent route of contamination. Here, we investigated whether the progression of GBS from carriage to disease is associated with genomic adaptation. Whole-genome comparison of 47 GBS samples from 19 mother-child pairs uncovered 21 single nucleotide polymorphisms (SNPs) and seven insertions/deletions. Of the SNPs detected, 16 appear to have been fixed in the population sampled whereas five mutations were found to be polymorphic. In the infant strains, 14 mutations were detected, including two independently fixed variants affecting the
covRS
locus, which is known to encode a major regulatory system of virulence. A one-nucleotide insertion was also identified in the promoter region of the highly immunogenic surface protein Rib gene. Gene expression analysis after incubation in human blood showed that these mutations influenced the expression of virulence-associated genes. Additional identification of three mutated strains in the mothers' milk raised the possibility of the newborns also being a source of contamination for their mothers. Overall, our work showed that GBS strains in carriage and disease scenarios might undergo adaptive changes following colonization. The types and locations of the mutations found, together with the experimental results showing their phenotypic impact, suggest that those in a context of infection were positively selected during the transition of GBS from commensal to pathogen, contributing to an increased capacity to cause disease.

IMPORTANCE
Group B
Streptococcus
(GBS) is a major pathogen responsible for neonatal infections. Considering that its colonization of healthy adults is mostly asymptomatic, the mechanisms behind its switch from a commensal to an invasive state are largely unknown. In this work, we compared the genomic profile of GBS samples causing infections in newborns with that of the GBS colonizing their mothers. Multiple mutations were detected, namely, within key virulence factors, including the response regulator CovR and surface protein Rib, potentially affecting the pathogenesis of GBS. Their overall impact was supported by differences in the expression of virulence-associated genes in human blood. Our results suggest that during GBS's progression to disease, particular variants are positively selected, contributing to the ability of this bacterium to infect its host.
From Homodimer to Heterodimer and Back: Elucidating the TonB Energy Transduction Cycle
Authors: Gresock Michael G. , Kastead Kyle A. , Postle Kathleen 
Published: August 2015

ABSTRACT

The TonB system actively transports large, scarce, and important nutrients through outer membrane (OM) transporters of Gram-negative bacteria using the proton gradient of the cytoplasmic membrane (CM). In
Escherichia coli
, the CM proteins ExbB and ExbD harness and transfer proton motive force energy to the CM protein TonB, which spans the periplasmic space and cyclically binds OM transporters. TonB has two activity domains: the amino-terminal transmembrane domain with residue H20 and the periplasmic carboxy terminus, through which it binds to OM transporters. TonB is inactivated by all substitutions at residue H20 except H20N. Here, we show that while TonB trapped as a homodimer through its amino-terminal domain retained full activity, trapping TonB through its carboxy terminus inactivated it by preventing conformational changes needed for interaction with OM transporters. Surprisingly, inactive TonB H20A had little effect on homodimerization through the amino terminus and instead decreased TonB carboxy-terminal homodimer formation prior to reinitiation of an energy transduction cycle. That result suggested that the TonB carboxy terminus ultimately interacts with OM transporters as a monomer. Our findings also suggested the existence of a separate equimolar pool of ExbD homodimers that are not in contact with TonB. A model is proposed where interaction of TonB homodimers with ExbD homodimers initiates the energy transduction cycle, and, ultimately, the ExbD carboxy terminus modulates interactions of a monomeric TonB carboxy terminus with OM transporters. After TonB exchanges its interaction with ExbD for interaction with a transporter, ExbD homodimers undergo a separate cycle needed to re-energize them.

IMPORTANCE
Canonical mechanisms of active transport across cytoplasmic membranes employ ion gradients or hydrolysis of ATP for energy. Gram-negative bacterial outer membranes lack these resources. The TonB system embodies a novel means of active transport across the outer membrane for nutrients that are too large, too scarce, or too important for diffusion-limited transport. A proton gradient across the cytoplasmic membrane is converted by a multiprotein complex into mechanical energy that drives high-affinity active transport across the outer membrane. This system is also of interest since one of its uses in pathogenic bacteria is for competition with the host for the essential element iron. Understanding the mechanism of the TonB system will allow design of antibiotics targeting iron acquisition.