Evolution of antibiotic resistance in gram-positive pathogens

Staphylococcus aureus is a common cause of soft tissue infection, e.g. impe tigo, cellulitis, or wound infection, and causes osteomyelitis, arthritis, bacteremia with metastatic infection, and scalded skin and toxic shock synd romes. Coagulase-negative staphylococci have become increasingly important causes of nosocomial bacteremia associated with invasive monitoring, intrav ascular catheters and prosthetic heart valves or joints. Most staphylococci produce b-lactamase and are resistant to penicillin. An increasing proport ion of S. aureus have intrinsic resistance to methicillin (MRSA) and presen t major problems in hospitals for the control of cross infection. The glyco peptides, teicoplanin and vancomycin, are the antibiotics of first choice f or treatment of these infections. After the first report describing a Japanese clinical isolate of vancomycin -resistant S, aureus (VRSA), several papers have documented the emergence o f these microorganisms, Since the development and spreading of this phenome non which is perceived as a fearsome threat to the already difficult therap y of nosocomial infections due to the prevalence of heterogeneous vancomyci n resistance, we found the incidence of MRSA exceeds 35% in our hospital. O ut of 179 methicillin-resistant S, aureus isolated during 1997-1998, two st rains (1.1%) gave subclones with vancomycin MICs of 8 mg/L. PFGE showed ide ntical restriction patterns for both isolates, suggesting transfer of a sin gle clone between two different patients.