title: In vivo development of decreased susceptibility to vancomycin in clinical isolates of methicillin-resistant Staphylococcus aureus.
abstract: To investigate the possibility of in vivo development of decreased vancomycin susceptibility, the vancomycin susceptibilities of 12 methicillin-resistant Staphylococcus aureus (MRSA) isolates serially recovered from six patients with vancomycin therapy were tested by standard MIC determination method and population analysis. While all of the MRSA isolates were susceptible to vancomycin (MICs, 1-2 microg/ml) by standard method, population analysis showed the upward shifts indicating decreased vancomycin susceptibility among serial isolates from two patients. These bacteria with decreased vancomycin susceptibility could be selected by using vancomycin selection of pre-therapy isolates under laboratory conditions. Furthermore, the reversion phenomenon of decreased vancomycin susceptibility was confirmed after 20 serial passages of the post-therapy isolates on drug-free agar. These data suggest that in vivo isolates may develop decreased vancomycin susceptibility that is not of such magnitude to cross a breakpoint threshold. This resistance may be unstable, and appears to result from a selective or inducible process that occurs in MRSA clinical strains during vancomycin therapy.
authors: The first Department of Internal Medicine, Nagoya University School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466-8560, Japan.
authors: Y
authors: Y
authors: Sugino
authors: Y
authors: Y
authors: Iinumab
authors: S
authors: S
authors: Ichiyama
authors: Y
authors: Y
authors: Ito
authors: S
authors: S
authors: Ohkawa
authors: N
authors: N
authors: Nakashima
authors: K
authors: K
authors: Shimokata
authors: Y
authors: Y
authors: Hasegawa
mesh_terms: D000368:Aged; D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D002675:Child, Preschool; D004269:DNA, Bacterial / Q000032:analysis; D004352:Drug Resistance, Microbial; D016521:Electrophoresis, Gel, Pulsed-Field; D005260:Female; D006801:Humans; D008297:Male; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D013203:Staphylococcal Infections / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification; D014640:Vancomycin / Q000494:pharmacology* / Q000627:therapeutic use
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D014640:Vancomycin