Emerging resistance in clinically important gram-positive cocci.

In the first half of the decade of the 1990s, we in the United States have seen the emergence and escalation of substantial antimicrobial resistance in medically important gram-positive cocci. The incidence of methicillin resistance of Staphylococcus aureus continues to increase (now 18%), resulting in many more isolates that are multiply resistant; all S aureus isolates are still susceptible to vancomycin. Enterococci, particularly Enterococcus faecium, have increasingly developed resistance to penicillin, gentamicin, streptomycin, and vancomycin (the last plasmid-mediated). More than a fourth of Streptococcus pneumoniae strains are now resistant to penicillin, and these strains tend to be multiply resistant, including to cephalosporins and macrolides.