Emergence of vancomycin resistance in Staphylococcus aureus

Background Since the emergence of methicillin-resistant Staphylococcus aure us, the glycopeptide vancomycin has been the only uniformly effective treat ment for staphylococcal infections. In 1997, two infections due to S. aureu s with reduced susceptibility to vancomycin were identified in the United S tates. Methods We investigated the two patients with infections due to S. aureus w ith intermediate resistance to glycopeptides, as defined by a minimal inhib itory concentration of vancomycin of 8 to 16 mu g per milliliter. To assess the carriage and transmission of these strains of S. aureus, we cultured s amples from the patients and their contacts and evaluated the isolates. Results The first patient was a 59-year-old man in Michigan with diabetes m ellitus and chronic renal failure. Peritonitis due to S. aureus with interm ediate resistance to glycopeptides developed after 18 weeks of vancomycin t reatment for recurrent methicillin-resistant S. aureus peritonitis associat ed with dialysis. The removal of the peritoneal catheter plus treatment wit h rifampin and trimethoprim-sulfamethoxazole eradicated the infection. The second patient was a 66-year-old man with diabetes in New Jersey. A bloodst ream infection due to S. aureus with intermediate resistance to glycopeptid es developed after 18 weeks of vancomycin treatment for recurrent methicill in-resistant S. aureus bacteremia. This infection was eradicated with vanco mycin, gentamicin, and rifampin. Both patients died. The glycopeptide-inter mediate S. aureus isolates differed by two bands on pulsed-field gel electr ophoresis. On electron microscopy, the isolates from the infected patients had thicker extracellular matrixes than control methicillin-resistant S. au reus isolates. No carriage was documented among 177 contacts of the two pat ients. Conclusions The emergence of S. aureus with intermediate resistance to glyc opeptides emphasizes the importance of the prudent use of antibiotics, the laboratory capacity to identify resistant strains, and the use of infection -control precautions to prevent transmission. (N Engl J Med 1999;340:493-50 1.) (C)1999, Massachusetts Medical Society.