scholarly journals Evaluation of Accessory Gene Regulator (agr) Group and Function in the Proclivity towards Vancomycin Intermediate Resistance in Staphylococcus aureus

2006 ◽  
Vol 51 (3) ◽  
pp. 1089-1091 ◽  
Author(s):  
Brian T. Tsuji ◽  
Michael J. Rybak ◽  
Kerry L. Lau ◽  
George Sakoulas
Keyword(s):  
Staphylococcus Aureus ◽  
Wild Type ◽  
Accessory Gene ◽  
Time Curve ◽  
Unbound Fraction ◽  
Accessory Gene Regulator ◽  
Intermediate Resistance ◽  
And Function ◽  
Type Strains

ABSTRACT Simulated therapeutic vancomycin exposures were evaluated against agr wild-type and knockout Staphylococcus aureus groups I, II, III, and IV using an in vitro pharmacodynamic model. All agr groups developed intermediate resistance to vancomycin after subtherapeutic exposure. The free unbound fraction of the area under the concentration-time curve (fAUC/MIC) required to suppress resistance was fourfold higher (P < 0.001) in agr dysfunctional strains (112 to 169) than that in parent wild-type strains (28).

scholarly journals Sequential Evolution of Vancomycin-Intermediate Resistance Alters Virulence in Staphylococcus aureus: Pharmacokinetic/Pharmacodynamic Targets for Vancomycin Exposure

2015 ◽  
Vol 60 (3) ◽  
pp. 1584-1591 ◽  
Author(s):  
Justin R. Lenhard ◽  
Tanya Brown ◽  
Michael J. Rybak ◽  
Calvin J. Meaney ◽  
Nicholas B. Norgard ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Galleria Mellonella ◽  
Infection Model ◽  
Bacterial Reduction ◽  
Accessory Gene ◽  
Time Curve ◽  
Bacterial Killing ◽  
Unbound Fraction ◽  
Content Type ◽  
Intermediate Resistance

Staphylococcus aureuspossesses exceptional virulence and a remarkable ability to adapt in the face of antibiotic therapy. We examined thein vitroevolution ofS. aureusin response to escalating vancomycin exposure by evaluating bacterial killing and the progression of resistance. A hollow-fiber infection model was utilized to simulate human doses of vancomycin increasing from 0.5 to 4 g every 12 h (q12h) versus a high inoculum (108CFU/ml) of methicillin-resistantS. aureus(MRSA) USA300 and USA400. Host-pathogen interactions usingGalleria mellonellaand accessory gene regulator (agr) expression were studied in serially obtained isolates. In both USA300 and USA400 MRSA isolates, vancomycin exposure up to 2 g q12h resulted in persistence and regrowth, whereas 4 g administered q12h achieved sustained killing against both strains. As vancomycin exposure increased from 0.5 to 2 g q12h, the bacterial population shifted toward vancomycin-intermediate resistance, and collateral increases in the MICs of daptomycin and televancin were observed over 10 days. Guideline-recommended exposure of a ratio of the area under the concentration-time curve for the free, unbound fraction of the drug to the MIC (fAUC/MIC ratio) of 200 displayed a 0.344-log bacterial reduction in area, whereasfAUC/MICs of 371 and 554 were needed to achieve 1.00- and 2.00-log reductions in area, respectively. The stepwise increase in resistance paralleled a decrease inG. mellonellamortality (P= 0.021) and a gradual decline of RNAIII expression over 10 days. Currently recommended doses of vancomycin resulted in amplification of resistance and collateral damage to other antibiotics. Decreases inagrexpression and virulence during therapy may be an adaptive mechanism ofS. aureuspersistence.

scholarly journals Comparative Efficacies of Human Simulated Exposures of Telavancin and Vancomycin against Methicillin-Resistant Staphylococcus aureus with a Range of Vancomycin MICs in a Murine Pneumonia Model

2010 ◽  
Vol 54 (12) ◽  
pp. 5115-5119 ◽  
Author(s):  
Jared L. Crandon ◽  
Joseph L. Kuti ◽  
David P. Nicolau
Keyword(s):  
Staphylococcus Aureus ◽  
Bacterial Load ◽  
Infection Model ◽  
Time Curve ◽  
Unbound Fraction ◽  
Methicillin Resistant ◽  
Vancomycin Mics ◽  
Mrsa Strains

ABSTRACT Telavancin displays potent in vitro and in vivo activity against methicillin-resistant Staphylococcus aureus (MRSA), including strains with reduced susceptibility to vancomycin. We compared the efficacies of telavancin and vancomycin against MRSA strains with vancomycin MICs of ≥1 μg/ml in a neutropenic murine lung infection model. Thirteen clinical MRSA isolates (7 vancomycin-susceptible, 2 vancomycin-heteroresistant [hVISA], and 4 vancomycin-intermediate [VISA] isolates) were tested after 24 h, and 7 isolates (1 hVISA and 4 VISA isolates) were tested after 48 h of exposure. Mice were administered subcutaneous doses of telavancin at 40 mg/kg of body weight every 12 h (q12h) or of vancomycin at 110 mg/kg q12h; doses were designed to simulate the area under the concentration-time curve for the free, unbound fraction of drug (fAUC) observed for humans given telavancin at 10 mg/kg q24h or vancomycin at 1 g q12h. Efficacy was expressed as the 24- or 48-h change in lung bacterial density from pretreatment counts. At dose initiation, the mean bacterial load was 6.16 ± 0.26 log10 CFU/ml, which increased by averages of 1.26 ± 0.55 and 1.74 ± 0.68 log in untreated mice after 24 and 48 h, respectively. At both time points, similar CFU reductions were noted for telavancin and vancomycin against MRSA, with vancomycin MICs of ≤2 μg/ml. Both drugs were similarly efficacious after 24 and 48 h of treatment against the hVISA strains tested. Against VISA isolates, telavancin reduced bacterial burdens significantly more than vancomycin for 1 of 4 isolates after 24 h and for 3 of 4 isolates after 48 h. These data support the potential utility of telavancin for the treatment of MRSA pneumonia caused by pathogens with reduced susceptibility to vancomycin.

scholarly journals Accessory Gene Regulator (agr) Locus in Geographically Diverse Staphylococcus aureus Isolates with Reduced Susceptibility to Vancomycin

2002 ◽  
Vol 46 (5) ◽  
pp. 1492-1502 ◽  
Author(s):  
George Sakoulas ◽  
George M. Eliopoulos ◽  
Robert C. Moellering ◽  
Christine Wennersten ◽  
Lata Venkataraman ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Parent Strain ◽  
Point Mutations ◽  
Loss Of Function ◽  
Accessory Gene ◽  
Accessory Gene Regulator ◽  
Geographic Origins ◽  
Group Ii ◽  
Null Strain

ABSTRACT The majority of infections with glycopeptide intermediate-level resistant Staphylococcus aureus (GISA) originate in biomedical devices, suggesting a possible increased ability of these strains to produce biofilm. Loss of function of the accessory gene regulator (agr) of S. aureus has been suggested to confer an enhanced ability to bind to polystyrene. We studied agr in GISA, hetero-GISA, and related glycopeptide-susceptible S. aureus isolates. All GISA strains from diverse geographic origins belong to agr group II. All GISA strains were defective in agr function, as demonstrated by their inability to produce delta-hemolysin. Hetero-GISA isolate A5940 demonstrated a nonsense mutation in agrA that was not present in a pulsed-field gel electrophoresis-indistinguishable vancomycin-susceptible isolate from the same patient. Various other agr point mutations were noted in several clinical GISA and hetero-GISA isolates. A laboratory-generated agr-null strain demonstrated a small but reproducible increase in vancomycin heteroresistance after growth in vitro in subinhibitory concentrations of vancomycin. This was not seen in the isogenic agr group II parent strain in which agr was intact. The in vitro bactericidal activity of vancomycin was attenuated in the agr-null strain compared to the parent strain. These findings imply that compromised agr function is advantageous to clinical isolates of S. aureus toward the development of vancomycin heteroresistance, perhaps through the development of vancomycin tolerance.

scholarly journals Toward Harmonization of Voriconazole CLSI and EUCAST Breakpoints for Candida albicans Using a Validated In Vitro Pharmacokinetic/Pharmacodynamic Model

2020 ◽  
Vol 64 (6) ◽  
Author(s):  
Maria-Ioanna Beredaki ◽  
Panagiota-Christina Georgiou ◽  
Maria Siopi ◽  
Lamprini Kanioura ◽  
David Andes ◽  
...  
Keyword(s):  
Candida Albicans ◽  
Simulation Analysis ◽  
Maximal Activity ◽  
Wild Type ◽  
Time Curve ◽  
Unbound Fraction ◽  
Content Type ◽  
Interval Probability

ABSTRACT CLSI and EUCAST susceptibility breakpoints for voriconazole and Candida albicans differ by one dilution (≤0.125 and ≤0.06 mg/liter, respectively) whereas the epidemiological cutoff values for EUCAST (ECOFF) and CLSI (ECV) are the same (0.03 mg/liter). We therefore determined the pharmacokinetic/pharmacodynamic (PK/PD) breakpoints of voriconazole against C. albicans for both methodologies with an in vitro PK/PD model, which was validated using existing animal PK/PD data. Four clinical wild-type and non-wild-type C. albicans isolates (voriconazole MICs, 0.008 to 0.125 mg/liter) were tested in an in vitro PK/PD model. For validation purposes, mouse PK were simulated and in vitro PD were compared with in vivo outcomes. Human PK were simulated, and the exposure-effect relationship area under the concentration-time curve for the free, unbound fraction of a drug from 0 to 24 h (fAUC0–24)/MIC was described for EUCAST and CLSI 24/48-h methods. PK/PD breakpoints were determined using the fAUC0–24/MIC associated with half-maximal activity (EI50) and Monte Carlo simulation analysis. The in vitro 24-h PD EI50 values of voriconazole against C. albicans were 2.5 to 5 (1.5 to 17) fAUC/MIC. However, the 72-h PD were higher at 133 (51 to 347) fAUC/MIC for EUCAST and 94 (35 to 252) fAUC/MIC for CLSI. The mean (95% confidence interval) probability of target attainment (PTA) was 100% (95 to 100%), 97% (72 to 100%), 83% (35 to 99%), and 49% (8 to 91%) for EUCAST and 100% (97 to 100%), 99% (85 to 100%), 91% (52 to 100%), and 68% (17 to 96%) for CLSI for MICs of 0.03, 0.06, 0.125, and 0.25 mg/liter, respectively. Significantly, >95% PTA values were found for EUCAST/CLSI MICs of ≤0.03 mg/liter. For MICs of 0.06 to 0.125 mg/liter, trough levels 1 to 4 mg/liter would be required to attain the PK/PD target. A PK/PD breakpoint of C. albicans voriconazole at the ECOFF/ECV of 0.03 mg/liter was determined for both the EUCAST and CLSI methods, indicating the need for breakpoint harmonization for the reference methodologies.

scholarly journals Correlation of vancomycin and daptomycin susceptibility in Staphylococcus aureus in reference to accessory gene regulator (agr) polymorphism and function

2007 ◽  
Vol 59 (6) ◽  
pp. 1190-1193 ◽  
Author(s):  
Warren E. Rose ◽  
Michael J. Rybak ◽  
Brian T. Tsuji ◽  
Glenn W. Kaatz ◽  
George Sakoulas
Keyword(s):  
Staphylococcus Aureus ◽  
Accessory Gene ◽  
Accessory Gene Regulator ◽  
And Function

scholarly journals Varied Contribution of Phospholipid Shedding From Membrane to Daptomycin Tolerance in Staphylococcus aureus

2021 ◽  
Vol 8 ◽  
Author(s):  
Tianwei Shen ◽  
Kelly M. Hines ◽  
Nathaniel K. Ashford ◽  
Brian J. Werth ◽  
Libin Xu
Keyword(s):  
Staphylococcus Aureus ◽  
Wild Type ◽  
Bacterial Membranes ◽  
Strain Pair ◽  
Time Kill ◽  
The Impact ◽  
Growth Controls ◽  
Type Strains ◽  
Spent Media

It has been suggested that daptomycin can be inactivated by lipids released by Staphylococcus aureus and that this effect is antagonized by phenol soluble modulins (PSMs), which bind to the shed lipids. PSM production is regulated by the Agr system, and others have shown that loss of the Agr function enhances S. aureus survival in the presence of daptomycin. Here we assessed the impact of Agr function on daptomycin activity and lipid metabolism under various conditions. Daptomycin activity was evaluated against three sets of isogenic strain series with wild-type or dysfunctional Agr using static daptomycin time-kills over 24 h and against one strain pair using in vitro pharmacokinetic/pharmacodynamic (PK/PD) models simulating clinical daptomycin exposure for 48 h. We performed comprehensive lipidomics on bacterial membranes and the spent media to correlate lipid shedding with survival. In static time-kill experiments, two agr-deficient strains (SH1000- and USA300 LAC ΔagrA) showed improved survival for 8 h compared with their corresponding wild-type strains as seen in previous studies, but this difference did not persist for 24 h. However, four other agr-deficient strains (SH1001 and JE2 agr KOs) did not demonstrate improved survival compared to isogenic wild-type strains at any time in the time-kills. Lipidomics analysis of SH1000, SH1001, and SH1000- strains showed daptomycin exposure increased lipid shedding compared to growth controls in all strains with phosphatidylglycerols (PGs), lysylPGs and cardiolipins predominating. In the cell pellets, PGs and lysylPGs decreased but cardiolipins were unchanged with daptomycin exposure. The shed lipid profiles in SH1001 and SH1000- were similar, suggesting that the inability to resist daptomycin by SH1001 was not because of differences in lipid shedding. In the PK/PD model, the agr mutant SH1000- strain did not show improved survival relative to SH1000 either. In conclusion, inactivation of daptomycin by shed lipids may be dependent on genetic background, the specific agr mutations, or the techniques used to generate these KOs rather than the overall function of the Agr system, and its contribution to daptomycin tolerance seems to be varied, transient, and growth-condition dependent.

Exploring the Role of Piperacillin and Tazobactam in Combination with Vancomycin against Methicillin-Resistant Staphylococcus aureus

Chemotherapy ◽  
2019 ◽  
Vol 64 (5-6) ◽  
pp. 233-237
Author(s):  
Thomas J. Dilworth ◽  
Daniel Sanchez ◽  
Beverly Anderson ◽  
Haedi DeAngelis ◽  
Renée-Claude Mercier
Keyword(s):  
Staphylococcus Aureus ◽  
Methicillin Resistant Staphylococcus Aureus ◽  
Accessory Gene ◽  
Methicillin Resistant ◽  
Accessory Gene Regulator ◽  
Antibiotic Susceptibilities ◽  
Strain Type ◽  
Time Kill

Previous studies have demonstrated synergy between piperacillin (PIP)-tazobactam (TAZ) (TZP) and vancomycin (VAN) against methicillin-resistant Staphylococcus aureus (MRSA). However, it is unknown whether PIP and/or TAZ synergizes with VAN against MRSA. We sought to determine whether PIP and/or TAZ synergizes with VAN against MRSA in vitro. The activity of PIP and/or TAZ with and without VAN (1/2 the minimum inhibitory concentration) was tested against 5 clinical MRSA isolates using a 24-h time-kill methodology. Antibiotic susceptibilities, accessory gene regulator (agr) operon functionality, and US strain type were also determined for the isolates. The combination of VAN and TZP was bactericidal against 3/5 isolates and synergistic against 4/5 isolates tested. Neither PIP nor TAZ alone combined with VAN demonstrated a significant reduction in bacterial growth. The combination of TZP and VAN was less active against the lone isolate with agr dysfunction. In summation, the combination of VAN with both PIP and TAZ was required for synergy against MRSA. This antibiotic combination may not be effective against unique MRSA strain types.

scholarly journals Reduced Susceptibility of Staphylococcus aureus to Vancomycin and Platelet Microbicidal Protein Correlates with Defective Autolysis and Loss of Accessory Gene Regulator (agr) Function

2005 ◽  
Vol 49 (7) ◽  
pp. 2687-2692 ◽  
Author(s):  
George Sakoulas ◽  
George M. Eliopoulos ◽  
Vance G. Fowler ◽  
Robert C. Moellering ◽  
Richard P. Novick ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Treated Patient ◽  
Accessory Gene ◽  
Accessory Gene Regulator ◽  
Vancomycin Mics ◽  
Platelet Microbicidal Protein ◽  
Triton X ◽  
Level Resistance

ABSTRACT Loss of agr function, vancomycin exposure, and abnormal autolysis have been linked with both development of the GISA phenotype and low-level resistance in vitro to thrombin-induced platelet microbicidal proteins (tPMPs). We examined the potential in vitro interrelationships among these parameters in well-characterized, isogenic laboratory-derived and clinical Staphylococcus aureus isolates. The laboratory-derived S. aureus strains included RN6607 (agrII-positive parent) and RN6607V (vancomycin-passaged variant; hetero-GISA), RN9120 (RN6607 agr::tetM; agr II knockout parent), RN9120V (vancomycin-passaged variant), and RN9120-GISA (vancomycin passaged, GISA). Two serial isolates from a vancomycin-treated patient with recalcitrant, methicillin-resistant S. aureus (MRSA) endocarditis were also studied: A5937 (agrII-positive initial isolate) and A5940 (agrII-defective/hetero-GISA isolate obtained after prolonged vancomycin administration). In vitro tPMP susceptibility phenotypes were assessed after exposure of strains to either 1 or 2 μg/ml. Triton X-100- and vancomycin-induced lysis profiles were determined spectrophotometrically. For agrII-intact strain RN6607, vancomycin exposure in vitro was associated with modest increases in vancomycin MICs and reduced killing by tPMP, but no change in lysis profiles. In contrast, vancomycin exposure of agrII-negative RN9120 yielded a hetero-GISA phenotype and was associated with defects in lysis and reduced in vitro killing by tPMP. In the clinical isolates, loss of agrII function during prolonged vancomycin therapy was accompanied by emergence of the hetero-GISA phenotype and reduced tPMP killing, with no significant change in lysis profiles. An association was identified between loss of agrII function and the emergence of hetero-GISA phenotype during either in vitro or in vivo vancomycin exposure. In vitro, these events were associated with defective lysis and reduced susceptibility to tPMP. The precise mechanism(s) underlying these findings is the subject of current investigations.

scholarly journals In Vitro Serial Passage of Staphylococcus aureus: Changes in Physiology, Virulence Factor Production, and agr Nucleotide Sequence

2002 ◽  
Vol 184 (5) ◽  
pp. 1430-1437 ◽  
Author(s):  
Greg A. Somerville ◽  
Stephen B. Beres ◽  
J. Ross Fitzgerald ◽  
Frank R. DeLeo ◽  
Robert L. Cole ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Hemolytic Activity ◽  
Specific Activity ◽  
Serial Passage ◽  
Wild Type ◽  
Coding Region ◽  
Toxic Shock ◽  
Accessory Gene ◽  
Aconitase Activity

ABSTRACT Recently, we observed that Staphylococcus aureus strains newly isolated from patients had twofold-higher aconitase activity than a strain passaged extensively in vitro, leading us to hypothesize that aconitase specific activity decreases over time during in vitro passage. To test this hypothesis, a strain recovered from a patient with toxic shock syndrome was serially passaged for 6 weeks, and the aconitase activity was measured. Aconitase specific activity decreased 38% (P < 0.001) by the sixth week in culture. During serial passage, S. aureus existed as a heterogeneous population with two colony types that had pronounced (wild type) or negligible zones of beta-hemolytic activity. The cell density-sensing accessory gene regulatory (agr) system regulates beta-hemolytic activity. Surprisingly, the percentage of colonies with a wild-type beta-hemolytic phenotype correlated strongly with aconitase specific activity (ρ = 0.96), suggesting a common cause of the decreased aconitase specific activity and the variation in percentage of beta-hemolytic colonies. The loss of the beta-hemolytic phenotype also coincided with the occurrence of mutations in the agrC coding region or the intergenic region between agrC and agrA in the derivative strains. Our results demonstrate that in vitro growth is sufficient to result in mutations within the agr operon. Additionally, our results demonstrate that S. aureus undergoes significant phenotypic and genotypic changes during serial passage and suggest that vigilance should be used when extrapolating data obtained from the study of high-passage strains.

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