scholarly journals Fate of Mutation Rate Depends onagrLocus Expression during Oxacillin-Mediated Heterogeneous-Homogeneous Selection in Methicillin-Resistant Staphylococcus aureus Clinical Strains

2011 ◽  
Vol 55 (7) ◽  
pp. 3176-3186 ◽  
Author(s):  
Konrad B. Plata ◽  
Roberto R. Rosato ◽  
Adriana E. Rosato
Keyword(s):  
Staphylococcus Aureus ◽  
Mutation Rate ◽  
Selection Process ◽  
Critical Role ◽  
Ectopic Expression ◽  
Regulatory System ◽  
Methicillin Resistant ◽  
Content Type ◽  
Heterogeneous Expression ◽  
Mrsa Strains

ABSTRACTMethicillin-resistantStaphylococcus aureus(MRSA) strains are characterized by a heterogeneous expression of resistance. We have previously shown in clinical oxacillin-susceptible,mecA-positive MRSA strains that selection from a very heterogeneous (HeR) to highly homogeneous (HoR) resistant phenotype was mediated by acquisition of mutations through an oxacillin-induced SOS response. In the present study, we used a spotted DNA microarray to evaluate differential gene expression during HeR-HoR selection and found increased expression of theagrtwo-component regulatory system. We hypothesized that increased expression ofagrrepresents a mechanistically relevant component of this process. We demonstrated that inactivation ofagrduring the HeR-HoR selection process results in a significant increase in mutation rate; these effects were reversed by complementing theagrmutant. Furthermore, we found that extemporal ectopic expression ofagrand, more specifically, RNAII inagr-null mutant HeR cells suppressed mutation frequency and the capacity of these cells to undergo the HeR-HoR selection. These findings sustain the concept that increased expression ofagrduring HeR-HoR selection plays a critical role in regulating the β-lactam-induced increased mutation rate in very heterogeneous MRSA strains. Moreover, they indicate that a temporally controlled increase inagrexpression is required to tightly modulate SOS-mediated mutation rates, which then allows for full expression of oxacillin homogeneous resistance in very heterogeneous clinical MRSA strains.

scholarly journals Role of the Accessory Gene Regulatoragrin Community-Associated Methicillin-Resistant Staphylococcus aureus Pathogenesis

2011 ◽  
Vol 79 (5) ◽  
pp. 1927-1935 ◽  
Author(s):  
Gordon Y. C. Cheung ◽  
Rong Wang ◽  
Burhan A. Khan ◽  
Daniel E. Sturdevant ◽  
Michael Otto
Keyword(s):  
Staphylococcus Aureus ◽  
Methicillin Resistance ◽  
Regulatory System ◽  
Accessory Gene ◽  
Methicillin Resistant ◽  
Content Type ◽  
Fibrinogen Binding ◽  
Gene Regulatory System ◽  
Differential Gene ◽  
Mrsa Strains

ABSTRACTThe molecular basis underlying the pathogenic success of community-associated methicillin-resistantStaphylococcus aureus(CA-MRSA) is not completely understood, but differential gene expression has been suggested to account at least in part for the high virulence of CA-MRSA strains. Here, we show that theagrgene regulatory system has a crucial role in the development of skin infections in the most prevalent CA-MRSA strain USA300. Importantly, our data indicate that this is due to discrepancies between theagrregulon of CA-MRSA and those of hospital-associated MRSA and laboratory strains. In particular,agrregulation in strain USA300 led to exceptionally strong expression of toxins and exoenzymes, upregulation of fibrinogen-binding proteins, increased capacity to bind fibrinogen, and increased expression of methicillin resistance genes. Our findings demonstrate thatagrfunctionality is critical for CA-MRSA disease and indicate that an adaptation of theagrregulon contributed to the evolution of highly pathogenic CA-MRSA.

scholarly journals Redefining the Role of the β-Lactamase Locus in Methicillin-Resistant Staphylococcus aureus: β-Lactamase Regulators Disrupt the MecI-Mediated Strong Repression onmecAand Optimize the Phenotypic Expression of Resistance in Strains with ConstitutivemecAExpression

2013 ◽  
Vol 57 (7) ◽  
pp. 3037-3045 ◽  
Author(s):  
Pedro Arêde ◽  
Joana Ministro ◽  
Duarte C. Oliveira
Keyword(s):  
Staphylococcus Aureus ◽  
Transcriptional Control ◽  
Phenotypic Expression ◽  
Regulatory System ◽  
Methicillin Resistant ◽  
Content Type ◽  
Resistance Determinants ◽  
Regulatory Systems ◽  
Mrsa Strains

ABSTRACTIn response to β-lactam chemotherapy,Staphylococcus aureushas acquired two resistance determinants:blaZ, coding for β-lactamase, which confers resistance to penicillins only, andmecA, coding for an extra cell wall cross-linking enzyme with reduced affinity for virtually all other β-lactams. The transcriptional control of both resistance determinants is regulated by homologous repressors (BlaI and MecI, respectively) and sensor inducers (BlaR1 and MecR1, respectively). There is a cross-talk between the two regulatory systems, and it has been demonstrated thatblaregulators stabilize themecAacquisition. In a recent study, we have unexpectedly observed that in most MRSA strains, there was no significant change in the resistance phenotype upon the overexpression intransof a MecI repressor, whereas in those few strains negative for theblalocus, there was a massive decrease of resistance (D. C. Oliveira and H. de Lencastre, PLoS One 6:e23287, 2011). Here, we demonstrate that, contrary to what is currently accepted, theblaregulatory system efficiently disrupts the strong MecI-mediated repression onmecA, enabling the optimal expression of resistance. This effect appears to be due to the formation of MecI::BlaI heterodimers that might bind less efficiently to themecApromoter and become nonfunctional due to the proteolytic inactivation of the BlaI monomer. In addition, we have also observed that the presence ofblaregulators may enhance dramatically the expression of β-lactam resistance in MRSA strains with constitutivemecAexpression, compensating for the fitness cost imposed by the large β-lactamase plasmid. These observations point to important unrecognized roles of theblalocus for the expression of the methicillin-resistantS. aureus(MRSA) phenotype.

scholarly journals Ceftaroline Is Active against Heteroresistant Methicillin-Resistant Staphylococcus aureus Clinical Strains despite Associated Mutational Mechanisms and Intermediate Levels of Resistance

2014 ◽  
Vol 58 (10) ◽  
pp. 5736-5746 ◽  
Author(s):  
Regina Fernandez ◽  
Liliana I. Paz ◽  
Roberto R. Rosato ◽  
Adriana E. Rosato
Keyword(s):  
Staphylococcus Aureus ◽  
Therapeutic Option ◽  
Gene Mutations ◽  
Sos Response ◽  
Methicillin Resistant ◽  
Content Type ◽  
Cell Wall Assembly ◽  
Heterogeneous Expression ◽  
Mechanistic Basis ◽  
Mrsa Strains

ABSTRACTMethicillin-resistantStaphylococcus aureus(MRSA) is an important infectious human pathogen responsible for diseases ranging from skin and soft tissue infections to life-threatening endocarditis. β-Lactam resistance in MRSA involves acquisition of penicillin-binding protein 2a (PBP2a), a protein with low affinity for β-lactams that mediates cell wall assembly when the normal staphylococcal PBPs (PBP1 to -4) are blocked by these agents. Many MRSA strains display heterogeneous expression of resistance (HeR) against β-lactam antibiotics. The β-lactam-mediated homoresistant (HoR) phenotype is associated with both expression of themecAgene and activation of the LexA-RecA-mediated SOS response, a regulatory network induced in response to DNA damage. Ceftaroline (CPT) is the only FDA-approved cephalosporin targeting PBP2a. We investigated the mechanistic basis of CPT activity against HeR-MRSA strains, including a set of strains displaying an intermediate level of resistance to CPT. Mechanistically, we found that 1 exposure of HeR-MRSA to subinhibitory concentrations of CPT selected for the HoR derivative activated the SOS response and increased mutagenesis. Importantly, CPT-selected HoR cells remained susceptible to CPT while still being resistant to most β-lactams, and 2-CPT activity in HeR-MRSA resided in an attenuated induction ofmecAexpression in comparison to other β-lactams. In addition, 3-CPT intermediate-resistant strains displayed a significant increase in CPT-inducedmecAexpression accompanied by mutations in PBP2, which together may interfere with the complete repression by CPT of both PBP2a and PBP2a-PBP2 interactions and thus be a determining factor in the low level of CPT resistance in the absence ofmecAgene mutations. The present study provides mechanistic evidence that CPT represents an alternative therapeutic option for the treatment of heteroresistant MRSA strains.

scholarly journals Evaluation of Ceftaroline Alone and in Combination against Biofilm-Producing Methicillin-Resistant Staphylococcus aureus with Reduced Susceptibility to Daptomycin and Vancomycin in anIn VitroPharmacokinetic/Pharmacodynamic Model

2015 ◽  
Vol 59 (8) ◽  
pp. 4497-4503 ◽  
Author(s):  
Katie E. Barber ◽  
Jordan R. Smith ◽  
Cortney E. Ireland ◽  
Blaise R. Boles ◽  
Warren E. Rose ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Medical Device ◽  
Bloodstream Infections ◽  
Methicillin Resistant ◽  
Content Type ◽  
Elimination Half ◽  
Antimicrobial Protection ◽  
Mrsa Strains ◽  
Post Hoc

ABSTRACTAnnually, medical device infections are associated with >250,000 catheter-associated bloodstream infections (CLABSI), with up to 25% mortality.Staphylococcus aureus, a primary pathogen in these infections, is capable of biofilm production, allowing organism persistence in harsh environments, offering antimicrobial protection. With increases inS. aureusisolates with reduced susceptibility to current agents, ceftaroline (CPT) offers a therapeutic alternative. Therefore, we evaluated whether CPT would have a role against biofilm-producing methicillin-resistantS. aureus(MRSA), including those with decreased susceptibilities to alternative agents. In this study, we investigated CPT activity alone or combined with daptomycin (DAP) or rifampin (RIF) against 3 clinical biofilm-producing MRSA strains in anin vitrobiofilm pharmacokinetic/pharmacodynamic (PK/PD) model. Simulated antimicrobial regimens were as follows: 600 mg of CPT every 8 h (q8h) (free maximum concentration of drug [fCmax], 17.04 mg/liter; elimination half-life [t1/2], 2.66 h), 12 mg/kg of body weight/day of DAP (fCmax, 14.7 mg/liter;t1/2, 8 h), and 450 mg of RIF q12h (fCmax, 3.5 mg/liter;t1/2, 3.4 h), CPT plus DAP, and CPT plus RIF. Samples were obtained and plated to determine colony counts. Differences in log10CFU/cm2were evaluated by analysis of variance with Tukey'spost hoctest. The strains were CPT and vancomycin susceptible and DAP nonsusceptible (DNS). CPT displayed activity throughout the experiment. DAP demonstrated initial activity with regrowth at 24 h in all strains. RIF was comparable to the drug-free control, and little benefit was observed when combined with CPT. CPT plus DAP displayed potent activity, with an average log10CFU/cm2reduction of 3.33 ± 1.01 from baseline. CPT demonstrated activity against biofilm-producing DNS MRSA. CPT plus DAP displayed therapeutic enhancement over monotherapy, providing a potential option for difficult-to-treat medical device infections.

scholarly journals Activities of Oxadiazole Antibacterials against Staphylococcus aureus and Other Gram-Positive Bacteria

2018 ◽  
Vol 62 (8) ◽  
Author(s):  
Sara Ceballos ◽  
Choon Kim ◽  
Derong Ding ◽  
Shahriar Mobashery ◽  
Mayland Chang ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Gram Positive ◽  
Methicillin Resistant ◽  
Content Type ◽  
Gram Positive Bacteria ◽  
Vancomycin Resistant Enterococci ◽  
Vancomycin Resistant ◽  
Mrsa Strains

ABSTRACT The activities of four oxadiazoles were investigated with 210 methicillin-resistant Staphylococcus aureus (MRSA) strains. MIC50 and MIC90 values of 1 to 2 and 4 μg/ml, respectively, were observed. We also evaluated the activity of oxadiazole ND-421 against other staphylococci and enterococci and in the presence of oxacillin for selected MRSA strains. The MIC for ND-421 is lowered severalfold in combination with oxacillin, as they synergize. The MIC90 of ND-421 against vancomycin-resistant enterococci is ≤1 μg/ml.

scholarly journals Differentiation of Community-Associated and Livestock-Associated Methicillin-Resistant Staphylococcus aureus Isolates and Identification of spa Types by Use of PCR and High-Resolution Melt Curve Analysis

2020 ◽  
Vol 58 (5) ◽  
Author(s):  
Seyed A. Ghorashi ◽  
Jane Heller ◽  
Quincy Zhang ◽  
Shafi Sahibzada
Keyword(s):  
Staphylococcus Aureus ◽  
High Resolution ◽  
Curve Analysis ◽  
Health Concern ◽  
Staphylococcal Protein A ◽  
Visual Interpretation ◽  
High Resolution Melt ◽  
Methicillin Resistant ◽  
Content Type ◽  
Mrsa Strains

ABSTRACT Infections due to methicillin-resistant Staphylococcus aureus (MRSA) are present worldwide and represent a major public health concern. The capability of PCR followed by high-resolution melt (HRM) curve analysis for the detection of community-associated and livestock-associated MRSA strains and the identification of staphylococcal protein A (spa) locus was evaluated in 74 MRSA samples which were isolated from the environment, humans, and pigs on a single piggery. PCR-HRM curve analysis identified four spa types among MRSA samples and differentiated MRSA strains accordingly. A nonsubjective differentiation model was developed according to genetic confidence percentage values produced by tested samples, which did not require visual interpretation of HRM curve results. The test was carried out at different settings, and result data were reanalyzed and confirmed with DNA sequencing. PCR-HRM curve analysis proved to be a robust and reliable test for spa typing and can be used as a tool in epidemiological studies.

scholarly journals Linezolid Attenuates Lethal Lung Damage during Postinfluenza Methicillin-Resistant Staphylococcus aureus Pneumonia

2019 ◽  
Vol 87 (10) ◽  
Author(s):  
Atul K. Verma ◽  
Christopher Bauer ◽  
Vijaya Kumar Yajjala ◽  
Shruti Bansal ◽  
Keer Sun
Keyword(s):  
Staphylococcus Aureus ◽  
Therapeutic Effect ◽  
Critical Role ◽  
Lung Damage ◽  
Alpha Toxin ◽  
Methicillin Resistant ◽  
Content Type ◽  
Linezolid Therapy ◽  
Staphylococcus Aureus Pneumonia ◽  
The Impact

ABSTRACT Postinfluenza methicillin-resistant Staphylococcus aureus (MRSA) infection can quickly develop into severe, necrotizing pneumonia, causing over 50% mortality despite antibiotic treatments. In this study, we investigated the efficacy of antibiotic therapies and the impact of S. aureus alpha-toxin in a model of lethal influenza virus and MRSA coinfection. We demonstrate that antibiotics primarily attenuate alpha-toxin-induced acute lethality, even though both alpha-toxin-dependent and -independent mechanisms significantly contribute to animal mortality after coinfection. Furthermore, we found that the protein synthesis-suppressing antibiotic linezolid has an advantageous therapeutic effect on alpha-toxin-induced lung damage, as measured by protein leak and lactate dehydrogenase (LDH) activity. Importantly, using a Panton-Valentine leucocidin (PVL)-negative MRSA isolate from patient sputum, we show that linezolid therapy significantly improves animal survival from postinfluenza MRSA pneumonia compared with vancomycin treatment. Rather than improved viral or bacterial control, this advantageous therapeutic effect is associated with a significantly attenuated proinflammatory cytokine response and acute lung damage in linezolid-treated mice. Together, our findings not only establish a critical role of alpha-toxin in the extreme mortality of secondary MRSA pneumonia after influenza but also provide support for the possibility that linezolid could be a more effective treatment than vancomycin to improve disease outcomes.

scholarly journals AUC/MIC Pharmacodynamic Target Is Not a Good Predictor of Vancomycin Efficacy in Methicillin-Resistant Staphylococcus aureus Experimental Endocarditis

2017 ◽  
Vol 61 (6) ◽  
Author(s):  
Ximena Castañeda ◽  
Cristina García-de-la-Mària ◽  
Oriol Gasch ◽  
Juan M. Pericas ◽  
Yolanda Armero ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Good Predictor ◽  
Methicillin Resistant Staphylococcus Aureus ◽  
Area Under The Curve ◽  
Methicillin Resistant ◽  
Bacterial Counts ◽  
Content Type ◽  
Treatment Groups ◽  
Mrsa Strains

ABSTRACT The aim of this in vivo study was to compare the efficacy of vancomycin at standard doses (VAN-SD) to that of VAN at adjusted doses (VAN-AD) in achieving a VAN area under the curve/MIC ratio (AUC/MIC) of ≥400 against three methicillin-resistant Staphylococcus aureus (MRSA) strains with different microdilution VAN MICs in an experimental endocarditis model. The valve vegetation bacterial counts after 48 h of VAN therapy were compared, and no differences were observed between the two treatment groups for any of the three strains tested. Overall, for VAN-SD and VAN-AD, the rates of sterile vegetations were 15/45 (33.3%) and 21/49 (42.8%) (P = 0.343), while the medians (interquartile ranges [IQRs]) for log10 CFU/g of vegetation were 2 (0 to 6.9) and 2 (0 to 4.5) (P = 0.384), respectively. In conclusion, this VAN AUC/MIC pharmacodynamic target was not a good predictor of vancomycin efficacy in MRSA experimental endocarditis.

scholarly journals Scope and Predictive Genetic/Phenotypic Signatures of Bicarbonate (NaHCO3) Responsiveness and β-Lactam Sensitization in Methicillin-Resistant Staphylococcus aureus

2020 ◽  
Vol 64 (5) ◽  
Author(s):  
Selvi C. Ersoy ◽  
Mariam Otmishi ◽  
Vanessa T. Milan ◽  
Liang Li ◽  
Youngju Pak ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Methicillin Resistant Staphylococcus Aureus ◽  
Clonal Complex ◽  
Population Analysis ◽  
Methicillin Resistant ◽  
Content Type ◽  
Mueller Hinton ◽  
Testing Medium ◽  
Mrsa Strains ◽  
Mueller Hinton Broth

ABSTRACT Addition of sodium bicarbonate (NaHCO3) to standard antimicrobial susceptibility testing medium reveals certain methicillin-resistant Staphylococcus aureus (MRSA) strains to be highly susceptible to β-lactams. We investigated the prevalence of this phenotype (NaHCO3 responsiveness) to two β-lactams among 58 clinical MRSA bloodstream isolates. Of note, ∼75% and ∼36% of isolates displayed the NaHCO3 responsiveness phenotype to cefazolin (CFZ) and oxacillin (OXA), respectively. Neither intrinsic β-lactam MICs in standard Mueller-Hinton broth (MHB) nor population analysis profiles were predictive of this phenotype. Several genotypic markers (clonal complex 8 [CC8]; agr I and spa t008) were associated with NaHCO3 responsiveness for OXA.

scholarly journals Complete Genome Sequences of Eight Methicillin-Resistant Staphylococcus aureus Strains Isolated from Patients in Japan

2019 ◽  
Vol 8 (47) ◽  
Author(s):  
Miyako Hikichi ◽  
Miki Nagao ◽  
Kazunori Murase ◽  
Chihiro Aikawa ◽  
Takashi Nozawa ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Soft Tissue ◽  
Complete Genome ◽  
Methicillin Resistant Staphylococcus Aureus ◽  
Clinical Manifestations ◽  
Invasive Disease ◽  
Genome Sequences ◽  
Methicillin Resistant ◽  
Content Type ◽  
Mrsa Strains

Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen causing nosocomial infections, and the clinical manifestations of MRSA range from asymptomatic colonization of the nasal mucosa to soft tissue infection to fulminant invasive disease. Here, we report the complete genome sequences of eight MRSA strains isolated from patients in Japan.

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