Changing susceptibilities of coagulase-negative staphylococci to teicoplanin in a teaching hospital

The susceptibility of two collections of coagulase-negative staphylococci ( CNS) isolated from clinical specimens for teicoplanin and vancomycin were c ompared. They comprised 91 and 101 isolates, collected in 1985 and 1994 res pectively, from different departments of a teaching hospital. MICs of vanco mycin and teicoplanin were determined by a modified Etest method. Additiona lly, a disc diffusion test was performed for teicoplanin. All isolates were susceptible to vancomycin (MIC less than or equal to 4 mg/L). Two of the 9 1 isolates collected in 1985 were intermediate to teicoplanin (MIC between 8 and 32 mg/L), whereas in 1994 the number of intermediate isolates was 20 out of 101 (P < 0.01). The correlation between MICs, as determined by the m odified Etest assay, and disc diffusion zones was poor (r = -0.35). Results show that resistance to teicoplanin in CNS has increased in the study hosp ital over a period of 9 years. This increase is likely to be correlated wit h the introduction of teicoplanin. Furthermore, a disc diffusion method doe s not appear to be the first method of choice for detection of strains of C NS with diminished susceptibility to teicoplanin.