In vitro exposure of community-associated methicillin-resistant Staphylococcus aureus (MRSA) strains to vancomycin: does vancomycin resistance occur?
Vancomycin is the preferred parenteral antibiotic for the treatment of all methicillin-resistant Staphylococcus aureus (MRSA) infections, including the newly emerging community-associated MRSA (CA-MRSA) infections. Vancomycin-intermediate nosocomial MRSA strains have developed in vitro and in vivo after exposure to vancomycin. The aim of this study was to determine whether daily serial passage of CA-MRSA strains onto vancomycin-supplemented agar selects for the development of vancomycin resistance. Twelve clinical isolates of the six commonest Australian and US strains of CA-MRSA were serially passaged daily for 25 days onto brain-heart infusion agar plates supplemented with 4 microg/mL vancomycin and then subcultured for a further 15 days onto antibiotic-free agar to assess the stability of the resistance phenotype. Minimum inhibitory concentrations (MICs) were determined by standard Etest every 5 days from day 0 to day 40. Serial passaging resulted in increased MICs in all strains but the rises were modest, with an increase of < 2 doubling dilutions. All strains remained vancomycin susceptible throughout the experiment according to Clinical Laboratory Standards Institute criteria.
Kleinschmidt
Sharon L
SL
Infection Management Service, Princess Alexandra Hospital, Ipswich Road, Woolloongabba, Brisbane, Qld 4102, Australia.
Munckhof
Wendy J
WJ
Nimmo
Graeme R
GR
D001315:Australia; D017714:Community-Acquired Infections / Q000188:drug therapy / Q000382:microbiology; D006801:Humans; D066298:In Vitro Techniques; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D013203:Staphylococcal Infections / Q000188:drug therapy / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification; D014481:United States; D014640:Vancomycin / Q000494:pharmacology*; D020713:Vancomycin Resistance
D014640:Vancomycin