Clinical isolates of Staphylococcus aureus from 1987 and 1989 demonstrating heterogeneous resistance to vancomycin and teicoplanin

Fifty isolates of Staphylococcus aureus, obtained during a multicenter clinical trial evaluating the efficacy of teicoplanin that was performed between 1987 and 1992, underwent glycopeptide susceptibility testing, and 2 isolates were found to be capable of growth on agar containing 4 or 8 mg/L of vancomycin. Both of these isolates were from patients that had received prolonged teicoplanin therapy and were deemed clinical failures. Extended susceptibility testing combined with mecA gene probing revealed that one isolate was susceptible to oxacillin, the other was resistant, and both were susceptible to a variety of nonglycopeptide agents. Population analyses revealed heterogeneous vancomycin- and teicoplanin-susceptibility profiles. Both strains were differentiated from recent glycopeptide intermediately resistant Staphylococcus aureus isolates by pulse-field analysis and by the fact that the resistance phenotype was stable to multiple serial passages. To our knowledge, this is the earliest report of S. aureus clinical isolates having reduced vancomycin and teicoplanin susceptibility.