title: Sequential Evolution of Vancomycin-Intermediate Resistance Alters Virulence in Staphylococcus aureus: Pharmacokinetic/Pharmacodynamic Targets for Vancomycin Exposure.
abstract: Staphylococcus aureus possesses exceptional virulence and a remarkable ability to adapt in the face of antibiotic therapy. We examined the in vitro evolution of S. aureus in 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 (10(8) CFU/ml) of methicillin-resistant S. aureus (MRSA) USA300 and USA400. Host-pathogen interactions using Galleria mellonella and 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, whereas fAUC/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 in G. mellonella mortality (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 in agr expression and virulence during therapy may be an adaptive mechanism of S. aureus persistence.
authors.affiliation: Laboratory for Antimicrobial Pharmacodynamics, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, Buffalo, New York, USA New York State Center of Excellence in Life Sciences and Bioinformatics, University at Buffalo, Buffalo, New York, USA.
authors.forename: Justin R
authors.initials: JR
authors.lastname: Lenhard
authors.affiliation: Laboratory for Antimicrobial Pharmacodynamics, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, Buffalo, New York, USA New York State Center of Excellence in Life Sciences and Bioinformatics, University at Buffalo, Buffalo, New York, USA.
authors.forename: Tanya
authors.initials: T
authors.lastname: Brown
authors.affiliation: Anti-Infective Research Laboratory, Eugene Applebaum College of Pharmacy and Health Sciences, Detroit, Michigan, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Rybak
authors.affiliation: Laboratory for Antimicrobial Pharmacodynamics, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, Buffalo, New York, USA New York State Center of Excellence in Life Sciences and Bioinformatics, University at Buffalo, Buffalo, New York, USA.
authors.forename: Calvin J
authors.initials: CJ
authors.lastname: Meaney
authors.affiliation: Laboratory for Antimicrobial Pharmacodynamics, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, Buffalo, New York, USA.
authors.forename: Nicholas B
authors.initials: NB
authors.lastname: Norgard
authors.affiliation: Laboratory for Antimicrobial Pharmacodynamics, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, Buffalo, New York, USA New York State Center of Excellence in Life Sciences and Bioinformatics, University at Buffalo, Buffalo, New York, USA.
authors.forename: Zackery P
authors.initials: ZP
authors.lastname: Bulman
authors.affiliation: Department of Pharmaceutical Sciences, University of New England, Portland, Maine, USA.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Brazeau
authors.affiliation: Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, New York, USA.
authors.forename: Steven R
authors.initials: SR
authors.lastname: Gill
authors.affiliation: Laboratory for Antimicrobial Pharmacodynamics, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, Buffalo, New York, USA New York State Center of Excellence in Life Sciences and Bioinformatics, University at Buffalo, Buffalo, New York, USA btsuji@buffalo.edu.
authors.forename: Brian T
authors.initials: BT
authors.lastname: Tsuji
mesh_terms: D000617:Aminoglycosides / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D017576:Daptomycin / Q000494:pharmacology; D054884:Host-Pathogen Interactions / Q000187:drug effects; D006801:Humans; D000077427:Lipoglycopeptides; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000472:pathogenicity*; D008826:Microbial Sensitivity Tests; D009036:Moths / Q000382:microbiology; D012329:RNA, Bacterial / Q000096:biosynthesis; D013203:Staphylococcal Infections / Q000188:drug therapy; D014640:Vancomycin / Q000494:pharmacology*; D020713:Vancomycin Resistance / Q000187:drug effects*
chemical_list: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D000077427:Lipoglycopeptides; D012329:RNA, Bacterial; C096035:RNAIII, Staphylococcus aureus; D014640:Vancomycin; D017576:Daptomycin; C487637:telavancin