scholarly journals A Novel, WidespreadqacAAllele Results in Reduced Chlorhexidine Susceptibility inStaphylococcus epidermidis

2019 ◽  
Vol 63 (6) ◽  
Author(s):  
Amin Addetia ◽  
Alexander L. Greninger ◽  
Amanda Adler ◽  
Shuhua Yuan ◽  
Negar Makhsous ◽  
...  
Keyword(s):  
Amino Acid ◽  
Staphylococcus Epidermidis ◽  
Sequence Data ◽  
Methicillin Resistance ◽  
Single Amino Acid ◽  
Data Sets ◽  
The Novel ◽  
Content Type

ABSTRACTChlorhexidine gluconate (CHG) is a topical antiseptic widely used in health care settings. InStaphylococcusspp., the pump QacA effluxes CHG, while the closely related QacB cannot due to a single amino acid substitution. We characterized 1,050 cutaneousStaphylococcusisolates obtained from 173 pediatric oncology patients enrolled in a multicenter CHG bathing trial. CHG susceptibility testing revealed that 63 (6%) of these isolates had elevated CHG MICs (≥4 μg/ml). Screening of all 1,050 isolates for theqacA/Bgene (the sameqacgene with A or B allele) by restriction fragment length polymorphism (RFLP) yielded 56 isolates with a novelqacA/BRFLP pattern,qacA/B273. The CHG MIC was significantly higher forqacA/B273-positive isolates (MIC50, 4 μg/ml; MIC range, 0.5 to 4 μg/ml) than for otherqacgroups:qacA-positive isolates (n = 559; MIC50, 1 μg/ml; MIC range, 0.5 to 4 μg/ml),qacB-positive isolates (n = 17; MIC50, 1 μg/ml; MIC range, 0.25 to 2 μg/ml), andqacA/B-negative isolates (n = 418, MIC50, 1 μg/ml; MIC range, 0.125 to 2 μg/ml) (P = 0.001). A high proportion of theqacA/B273-positive isolates also displayed methicillin resistance (96.4%) compared to the otherqacgroups (24.9 to 61.7%) (P = 0.001). Whole-genome sequencing revealed thatqacA/B273-positive isolates encoded a variant of QacA with 2 amino acid substitutions. This new allele, namedqacA4, was carried on the novel plasmid pAQZ1. TheqacA4-carrying isolates belonged to the highly resistantStaphylococcus epidermidissequence type 2 clone. By searching available sequence data sets, we identified 39 additionalqacA4-carryingS. epidermidisstrains from 5 countries. Curing an isolate ofqacA4resulted in a 4-fold decrease in the CHG MIC, confirming the role ofqacA4in the elevated CHG MIC. Our results highlight the importance of further studyingqacA4and its functional role in clinical staphylococci.

scholarly journals Exploring the Role of the Ω-Loop in the Evolution of Ceftazidime Resistance in the PenA β-Lactamase from Burkholderia multivorans, an Important Cystic Fibrosis Pathogen

2016 ◽  
Vol 61 (2) ◽  
Author(s):  
Krisztina M. Papp-Wallace ◽  
Scott A. Becka ◽  
Magdalena A. Taracila ◽  
Elise T. Zeiser ◽  
Julian A. Gatta ◽  
...  
Keyword(s):  
Amino Acid ◽  
Burkholderia Cepacia ◽  
Clinical Isolates ◽  
Dynamics Simulation ◽  
Single Amino Acid ◽  
Amino Acid Substitutions ◽  
Biochemical Basis ◽  
Content Type ◽  
Burkholderia Multivorans

ABSTRACT The unwelcome evolution of resistance to the advanced generation cephalosporin antibiotic, ceftazidime is hindering the effective therapy of Burkholderia cepacia complex (BCC) infections. Regrettably, BCC organisms are highly resistant to most antibiotics, including polymyxins; ceftazidime and trimethoprim-sulfamethoxazole are the most effective treatment options. Unfortunately, resistance to ceftazidime is increasing and posing a health threat to populations susceptible to BCC infection. We found that up to 36% of 146 tested BCC clinical isolates were nonsusceptible to ceftazidime (MICs ≥ 8 μg/ml). To date, the biochemical basis for ceftazidime resistance in BCC is largely undefined. In this study, we investigated the role of the Ω-loop in mediating ceftazidime resistance in the PenA β-lactamase from Burkholderia multivorans, a species within the BCC. Single amino acid substitutions were engineered at selected positions (R164, T167, L169, and D179) in the PenA β-lactamase. Cell-based susceptibility testing revealed that 21 of 75 PenA variants engineered in this study were resistant to ceftazidime, with MICs of >8 μg/ml. Under steady-state conditions, each of the selected variants (R164S, T167G, L169A, and D179N) demonstrated a substrate preference for ceftazidime compared to wild-type PenA (32- to 320-fold difference). Notably, the L169A variant hydrolyzed ceftazidime significantly faster than PenA and possessed an ∼65-fold-lower apparent Ki (Ki app) than that of PenA. To understand why these amino acid substitutions result in enhanced ceftazidime binding and/or turnover, we employed molecular dynamics simulation (MDS). The MDS suggested that the L169A variant starts with the most energetically favorable conformation (−28.1 kcal/mol), whereas PenA possessed the most unfavorable initial conformation (136.07 kcal/mol). In addition, we observed that the spatial arrangement of E166, N170, and the hydrolytic water molecules may be critical for enhanced ceftazidime hydrolysis by the L169A variant. Importantly, we found that two clinical isolates of B. multivorans possessed L169 amino acid substitutions (L169F and L169P) in PenA and were highly resistant to ceftazidime (MICs ≥ 512 μg/ml). In conclusion, substitutions in the Ω-loop alter the positioning of the hydrolytic machinery as well as allow for a larger opening of the active site to accommodate the bulky R1 and R2 side chains of ceftazidime, resulting in resistance. This analysis provides insights into the emerging phenotype of ceftazidime-resistant BCC and explains the evolution of amino acid substitutions in the Ω-loop of PenA of this significant clinical pathogen.

scholarly journals A Trigger Residue for Transmembrane Signaling in the Escherichia coli Serine Chemoreceptor

2015 ◽  
Vol 197 (15) ◽  
pp. 2568-2579 ◽  
Author(s):  
Smiljka Kitanovic ◽  
Peter Ames ◽  
John S. Parkinson
Keyword(s):  
Escherichia Coli ◽  
Amino Acid ◽  
Single Amino Acid ◽  
Side Chain ◽  
Transmembrane Signaling ◽  
Synthetic Control ◽  
Content Type ◽  
Output State ◽  
Cable Segment

ABSTRACTThe transmembrane Tsr protein ofEscherichia colimediates chemotactic responses to environmental serine gradients. Serine binds to the periplasmic domain of the homodimeric Tsr molecule, promoting a small inward displacement of one transmembrane helix (TM2). TM2 piston displacements, in turn, modulate the structural stability of the Tsr-HAMP domain on the cytoplasmic side of the membrane to control the autophosphorylation activity of the signaling CheA kinase bound to the membrane-distal cytoplasmic tip of Tsr. A five-residue control cable segment connects TM2 to the AS1 helix of HAMP and transmits stimulus and sensory adaptation signals between them. To explore the possible role of control cable helicity in transmembrane signaling by Tsr, we characterized the signaling properties of mutant receptors with various control cable alterations. An all-alanine control cable shifted Tsr output toward the kinase-on state, whereas an all-glycine control cable prevented Tsr from reaching either a fully on or fully off output state. Restoration of the native isoleucine (I214) in these synthetic control cables largely alleviated their signaling defects. Single amino acid replacements at Tsr-I214 shifted output toward the kinase-off (L, N, H, and R) or kinase-on (A and G) states, whereas other control cable residues tolerated most amino acid replacements with little change in signaling behavior. These findings indicate that changes in control cable helicity might mediate transitions between the kinase-on and kinase-off states during transmembrane signaling by chemoreceptors. Moreover, the Tsr-I214 side chain plays a key role, possibly through interaction with the membrane interfacial environment, in triggering signaling changes in response to TM2 piston displacements.IMPORTANCEThe Tsr protein ofE. colimediates chemotactic responses to environmental serine gradients. Stimulus signals from the Tsr periplasmic sensing domain reach its cytoplasmic kinase control domain through piston displacements of a membrane-spanning helix and an adjoining five-residue control cable segment. We characterized the signaling properties of Tsr variants to elucidate the transmembrane signaling role of the control cable, an element present in many microbial sensory proteins. Both the kinase-on and kinase-off output states of Tsr depended on control cable helicity, but only one residue, I214, was critical for triggering responses to attractant inputs. These findings suggest that signal transmission in Tsr involves modulation of control cable helicity through interaction of the I214 side chain with the cytoplasmic membrane.

scholarly journals A novelqacAallele results in an elevated chlorhexidine glu conate minimum inhibitory concentration in cutaneousStaphylococcus epidermidisisolates

2018 ◽  
Author(s):  
Amin Addetia ◽  
Alexander L Greninger ◽  
Amanda Adler ◽  
Shuhua Yuan ◽  
Negar Makhsous ◽  
...  
Keyword(s):  
United States ◽  
Amino Acid ◽  
Pediatric Oncology ◽  
Methicillin Resistance ◽  
The United States ◽  
Chlorhexidine Gluconate ◽  
Single Amino Acid ◽  
The Novel ◽  
Oncology Patients ◽  
Clonal Type

AbstractChlorhexidine gluconate (CHG) is a topical antiseptic widely used in healthcare settings. InStaphylococcusspp., the pump QacA effluxes CHG, while the closely related QacB cannot due to a single amino acid substitution. We characterized 1,050 cutaneousStaphylococcusisolates obtained from 173 pediatric oncology patients enrolled in a multicenter CHG bathing trial. CHG susceptibility testing revealed 63 (6%) of these isolates had elevated CHG MICs (≥ 4 μg/mL). Screening of all 1,050 isolates forqacA/Bby restriction fragment length polymorphism (RFLP) yielded 56 isolates with a novelqacA/BRFLP pattern,qacAB273. The CHG MIC was significantly higher forqacAB273-positive isolates (MIC50: 4 μg/mL, [range: 0.5 – 4 μg/mL]) compared to otherqacgroups:qacA-positive (n=559, 1 μg/mL, [0.5 – 4 μg/mL]),qacB-positive (n=17, 1 μg/mL, [0.25 – 2 μg/mL]), andqacA/B-negative (n=418, 1 μg/mL, [0.125 – 2 μg/mL], p=0.001). TheqacAB273-positive isolates also displayed a high proportion of methicillin resistance (96.4%) compared to otherqacgroups (24.9 – 61.7%, p=0.001). Whole genome sequencing revealed thatqacAB273-positive isolates encoded a variant of QacA with 2 amino acid substitutions. This new allele, namedqacA4, was carried on the novel plasmid pAQZ1. TheqacA4-carrying isolates belonged to the highly resistantS. epidermidisclone ST2 and were collected from multiple centers across the United States and Canada. Curing an isolate ofqacA4resulted in a four-fold decrease in the CHG MIC, confirming the role ofqacA4in the elevated CHG MIC. Our results highlight the importance of further studyingqacA4and its functional role in clinical staphylococci.ImportanceStaphylococcus epidermidisis an important cause of infections in patients with implanted devices. Bathing with chlorhexidine gluconate (CHG), a topical antiseptic, has been shown to reduce rates of device-associated infections, especially those caused byS. epidermidis. InS. epidermidis, reduced susceptibility to CHG is associated with carriage of theqacAgene. As part of a multicenter CHG bathing trial, we obtained cutaneousStaphylococcusisolates from pediatric oncology patients across the United States and Canada. We identified a group of isolates capable of surviving in higher concentrations of CHG and determined a novel allele ofqacA, termedqacA4and carried on the novel plasmid pAQZ1, was responsible for the isolates’ survival in higher CHG concentrations. TheqacA4-carryingS. epidermidisisolates belonged to the highly resistant and virulent ST2 clonal type. Our results highlight the need to understand the global distribution of novelqacAalleles, includingqacA4, and their mechanistic effect on efflux.

Neurofibromatosis type 2: growth stimulation of mixed acoustic schwannoma by concurrent adjacent meningioma: possible role of growth factors

1998 ◽  
Vol 89 (1) ◽  
pp. 149-154 ◽  
Author(s):  
Roberto Pallini ◽  
Angelo Tancredi ◽  
Patrizia Casalbore ◽  
Delio Mercanti ◽  
Luigi M. Larocca ◽  
...  
Keyword(s):  
Neurofibromatosis Type ◽  
Growth Stimulation ◽  
Neurofibromatosis Type 2 ◽  
Annual Growth Rate ◽  
Content Type ◽  
Acoustic Schwannoma ◽  
Epidermal Growth ◽  
The One

✓ The authors report the case of a young man suffering from neurofibromatosis type 2 (NF2) who harbored bilateral acoustic schwannomas and a parasellar meningioma. Neuroimaging studies performed during a 4-year follow-up period showed that the bilateral schwannomas had grown very little and at similar rates. However, after the meningioma had infiltrated the tentorium and approached the ipsilateral schwannoma at the incisura, both Schwann cell tumors started to grow rapidly, particularly the one adjacent to the meningioma, of which the percentage of annual growth rate increased by approximately a factor of 102. At the same time, magnetic resonance imaging showed that this tumor also changed its features. During surgery, the acoustic schwannoma was firmly adherent to both meningioma and tentorium. Histological examination revealed meningotheliomatous cells in the schwannoma adjacent to the meningioma. Antiphosphotyrosine immunoblotting of PC12 cells was compatible with the presence of an epidermal growth factor (EGF)—like molecule in the cerebrospinal fluid (CSF) of the patient. This factor was not detected in the CSF of five other NF2 patients, two of whom bore associated bilateral acoustic schwannomas and meningioma in remote locations. It is hypothesized that the meningotheliomatous cells infiltrating the schwannoma triggered an autocrine/paracrine growth—stimulatory mechanism that involved an EGF-like factor.

scholarly journals PFM-Like Enzymes Are a Novel Family of Subclass B2 Metallo-β-Lactamases from Pseudomonas synxantha Belonging to the Pseudomonas fluorescens Complex

2019 ◽  
Vol 64 (2) ◽  
Author(s):  
Laurent Poirel ◽  
Mattia Palmieri ◽  
Michael Brilhante ◽  
Amandine Masseron ◽  
Vincent Perreten ◽  
...  
Keyword(s):  
Amino Acid ◽  
Pseudomonas Fluorescens ◽  
Bacterial Species ◽  
Amino Acid Identity ◽  
Chicken Meat ◽  
The Novel ◽  
Content Type ◽  
Acid Identity ◽  
Carbapenem Resistant ◽  
Encoding Genes

ABSTRACT A carbapenem-resistant Pseudomonas synxantha isolate recovered from chicken meat produced the novel carbapenemase PFM-1. That subclass B2 metallo-β-lactamase shared 71% amino acid identity with β-lactamase Sfh-1 from Serratia fonticola. The blaPFM-1 gene was chromosomally located and likely acquired. Variants of PFM-1 sharing 90% to 92% amino acid identity were identified in bacterial species belonging to the Pseudomonas fluorescens complex, including Pseudomonas libanensis (PFM-2) and Pseudomonas fluorescens (PFM-3), highlighting that these species constitute reservoirs of PFM-like encoding genes.

scholarly journals Cryptococcus neoformans Evades Pulmonary Immunity by Modulating Xylose Precursor Transport

2020 ◽  
Vol 88 (8) ◽  
Author(s):  
Lucy X. Li ◽  
Camaron R. Hole ◽  
Javier Rangel-Moreno ◽  
Shabaana A. Khader ◽  
Tamara L. Doering
Keyword(s):  
Cryptococcus Neoformans ◽  
Mutant Strain ◽  
Fungal Pathogen ◽  
Wild Type ◽  
Content Type ◽  
Helper Cell Type ◽  
Lymphoid Structures ◽  
Type Infection

ABSTRACT Cryptococcus neoformans is a fungal pathogen that kills almost 200,000 people each year and is distinguished by abundant and unique surface glycan structures that are rich in xylose. A mutant strain of C. neoformans that cannot transport xylose precursors into the secretory compartment is severely attenuated in virulence in mice yet surprisingly is not cleared. We found that this strain failed to induce the nonprotective T helper cell type 2 (Th2) responses characteristic of wild-type infection, instead promoting sustained interleukin 12p40 (IL-12p40) induction and increased IL-17A (IL-17) production. It also stimulated dendritic cells to release high levels of proinflammatory cytokines, a behavior we linked to xylose expression. We further discovered that inducible bronchus-associated lymphoid tissue (iBALT) forms in response to infection with either wild-type cryptococci or the mutant strain with reduced surface xylose; although iBALT formation is slowed in the latter case, the tissue is better organized. Finally, our temporal studies suggest that lymphoid structures in the lung restrict the spread of mutant fungi for at least 18 weeks after infection, which is in contrast to ineffective control of the pathogen after infection with wild-type cells. These studies demonstrate the role of xylose in modulation of host response to a fungal pathogen and show that cryptococcal infection triggers iBALT formation.

scholarly journals Records in contexts: the road of archives to semantic interoperability

2017 ◽  
Vol 51 (4) ◽  
pp. 387-405 ◽  
Author(s):  
Dunia Llanes-Padrón ◽  
Juan-Antonio Pastor-Sánchez
Keyword(s):  
Semantic Web ◽  
Conceptual Model ◽  
Semantic Interoperability ◽  
Data Sets ◽  
Semantic Web Technologies ◽  
Content Type ◽  
Web Technologies ◽  
The Road ◽  
Owl Ontology

Purpose The purpose of this paper is to examine the Records in Contexts proposal of a conceptual model (RiC-CM) from the International Council on Archives’ (ICA) archival description and to propose an OWL ontology for its implementation in the semantic web. Design/methodology/approach The various elements of the model are studied and are related to earlier norms in order to understand their structure and the modeling of the ontology. Findings The analysis reveals the integrating nature of RiC-CM and the possibilities it offers for greater interoperability of data from archival descriptions. Two versions of an OWL ontology were developed to represent the conceptual model. The first makes a direct transposition of the conceptual model; the second optimizes the properties and relations in order to simplify the use and maintenance of the ontology. Research limitations/implications The proposed ontology will follow the considerations of the final version of the ICA’s RiC-CM. Practical implications The analysis affords an understanding of the role of RiC-CM in publishing online archival data sets, while the ontology is an initial approach to the semantic web technologies involved. Originality/value This paper offers an overview of Records in Contexts with respect to the advantages in the field of semantic interoperability, and supposes the first proposal of an ontology based on the conceptual model.

scholarly journals Dissection of the Role of Pili and Type 2 and 3 Secretion Systems in Adherence and Biofilm Formation of an Atypical Enteropathogenic Escherichia coli Strain

2013 ◽  
Vol 81 (10) ◽  
pp. 3793-3802 ◽  
Author(s):  
Rodrigo T. Hernandes ◽  
Miguel A. De la Cruz ◽  
Denise Yamamoto ◽  
Jorge A. Girón ◽  
Tânia A. T. Gomes
Keyword(s):  
Escherichia Coli ◽  
Biofilm Formation ◽  
Coli Strain ◽  
Mass Spectrometry Analysis ◽  
Secretion Systems ◽  
Content Type ◽  
Spectrometry Analysis ◽  
Rigid Rod

ABSTRACTAtypical enteropathogenicEscherichia coli(aEPEC) strains are diarrheal pathogens that lack bundle-forming pilus production but possess the virulence-associated locus of enterocyte effacement. aEPEC strain 1551-2 produces localized adherence (LA) on HeLa cells; however, its isogenic intimin (eae) mutant produces a diffuse-adherence (DA) pattern. In this study, we aimed to identify the DA-associated adhesin of the 1551-2eaemutant. Electron microscopy of 1551-2 identified rigid rod-like pili composed of an 18-kDa protein, which was identified as the major pilin subunit of type 1 pilus (T1P) by mass spectrometry analysis. Deletion offimAin 1551-2 affected biofilm formation but had no effect on adherence properties. Analysis of secreted proteins in supernatants of this strain identified a 150-kDa protein corresponding to SslE, a type 2 secreted protein that was recently reported to be involved in biofilm formation of rabbit and human EPEC strains. However, neither adherence nor biofilm formation was affected in a 1551-2sslEmutant. We then investigated the role of the EspA filament associated with the type 3 secretion system (T3SS) in DA by generating a doubleeae espAmutant. This strain was no longer adherent, strongly suggesting that the T3SS translocon is the DA adhesin. In agreement with these results, specific anti-EspA antibodies blocked adherence of the 1551-2eaemutant. Our data support a role for intimin in LA, for the T3SS translocon in DA, and for T1P in biofilm formation, all of which may act in concert to facilitate host intestinal colonization by aEPEC strains.

Sign in / Sign up

Export Citation Format

Share Document