METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS - MICROBIOLOGIC CHARACTERISTICS, ANTIMICROBIAL SUSCEPTIBILITIES, AND ASSESSMENT OF VIRULENCE OF AN EPIDEMIC STRAIN

An epidemic strain of methicillin-resistance S. aureus (MRSA) isolated from patients at the University of Virginia Hospital in Charlottesville (MRSA-Va) (Virginia, USA) was characterized; virulence properties of this strain were compared with those of 3 clinically significant strains of methicillin-sensitive S. aureus. Unlike most known strains of MRSA, MRSA-Va was sensitive to tetracycline and streptomycin and exhibited high-level homogeneous methicillin resistance (minimal inhibitory concentration, > 128 .mu.g/ml). The expression of resistance was not influenced by incubation temperature. MRSA-Va contained significantly more catalase (P < 0.05) than methicillin-sensitive strains but about the same amount of protein A. Phagocytosis and killing of MRSA-Va by normal polymorphonuclear leukocytes were not significantly different from that of Wood-46 strain of S. aureus. In mouse virulence studies using both i.p. and i.v. modes of infection, 50% lethal doses for MRSA-Va were comparable with those of the 3 methicillin-sensitive strains. This epidemic strain of MRSA appears to be fully virulent.