Changes in drug susceptibility and toxin genes in Staphylococcus aureus isolated from blood cultures at a university hospital.

We studied changes in toxin-producing genes and drug susceptibility in Staphylococcus aureus isolated from blood cultures at the University of Tokyo Hospital between 1980-1984 (six mecA gene-positive methicillin resistant S. aureus [MRSA] strains and 20 mecA gene-negative methicillin-susceptible S. aureus [MSSA] strains) and 1999 (11 MRSA and 20 MSSA strains). The prevalence of strains with toxin-producing genes increased from 66.7% to 90.9% in MRSA, and from 30.0% to 55.0% in MSSA during the interval. Among toxin-producing gene-positive S. aureus, the dominant strains shifted from those with the enterotoxin (ET) - A gene in 1980-1984 to those with both the toxic shock syndrome toxin-1 and the ET-C genes in 1999. All strains were susceptible to vancomycin and teicoplanin. Mupirocin and arbekacin inhibited all strains at concentrations of less than or equal to 0.5 micro g/ml and 4 micro g/ml, respectively. More than half of the MRSA strains in 1999 were considered to be nonsusceptible to flomoxef. Because almost all MRSA and more than half of MSSA among recently isolated strains possessed the toxin-producing genes, we should pay attention to whether toxin-related diseases caused by MRSA and MSSA are increasing.