In Vitro Susceptibilities and Molecular Analysis of Vancomycin-Intermediate and Vancomycin- Resistant Staphylococcus aureus Isolates

Background. There is increasing frequency of vancomycin-intermediate and-resistant Staphylococcus aureus (VISA and VRSA) isolates identified in clinical practice. There are limited reports evaluating susceptibility pat-terns and molecular characteristics of these strains. Methods. Laboratory analysis was performed on 13 VRSA and 33 VISA isolates, including susceptibility testing by broth microdilution, detection of Panton-Valentine leukocidin (PVL) genes, arginine catabolic mobile element (ACME), and staphylococcal cassette chromosome mec typing using polymerase chain reaction. Strain typing using pulsed-field gel electrophoresis (PFGE) was performed on VRSA isolates. Results. Telavancin, linezolid, tigecycline, and minocycline were active against>90 % of VISA isolates, while>90 % of VRSA isolates were susceptible to ceftaroline, daptomycin, linezolid, minocyline, tigecycline, rifampin, and trimethoprim/sulfamethoxazole. There were no VISA or VRSA isolates that carried PVL genes or ACME, and most strains (69.8%) were staphylococcal cassette chromosome mec type II. VRSA isolates were predominantly related to USA100 (53.8%) and none were related to USA300 or USA400. Conclusions. A large number of available antimicrobial agents retain very good in vitro activity against VRSA and VISA isolates. The present isolates appear to be derived from healthcare-associated strains based on the absence of features associated with community-associated strains, and VRSA isolates are polyclonal by PFGE. Vancomycin is currently the most frequently prescribe