Evolution of antibiotic resistance in gram-positive pathogens

Staphylococcus aureus is a common cause of soft tissue infection, e.g. impetigo, cellulitis, or wound infection, and causes osteomyelitis, arthritis, bacteremia with metastatic infection, and scalded skin and toxic shock syndromes. Coagulase-negative staphylococci have become increasingly important causes of nosocomial bacteremia associated with invasive monitoring, intravascular catheters and prosthetic heart valves or joints. Most staphylococci produce b-lactamase and are resistant to penicillin. An increasing proportion of S. aureus have intrinsic resistance to methicillin (MRSA) and present major problems in hospitals for the control of cross infection. The glycopeptides, teicoplanin and vancomycin, are the antibiotics of first choice for 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 of these microorganisms. Since the development and spreading of this phenomenon which is perceived as a fearsome threat to the already difficult therapy of nosocomial infections due to the prevalence of heterogeneous vancomycin resistance, we found the incidence of MRSA exceeds 35% in our hospital. Out of 179 methicillin-resistant S. aureus isolated during 1997-1998, two strains (1.1%) gave subclones with vancomycin MICs of 8 mg/L. PFGE showed identical restriction patterns for both isolates, suggesting transfer of a single clone between two different patients.