Comparison of teicoplanin and vancomycin in vitro activity on clinical isolates of Staphylococcus aureus

Ninety-one clinical isolates of Staphylococcus aureus have been tested with the Kirby Bauer and the Etest® method to determine the susceptibility to glycopeptides in the 2007-2010 period. Five strains (5.5%) were resistant to vancomycin and nine (9.9%) to teicoplanin. Teicoplanin showed a median minimal inhibitory concentration (MIC) of 1 mg/l (range 0.125-24 mg/l), an MIC50 of 1 mg/l, and an MIC90 of 2 mg/l; vancomycin had a median MIC of 1.5 mg/l (range 0.38-4 mg/l), an MIC50 of 1.5 mg/l, and an MIC90 of 2 mg/l. More isolates were distributed on higher values of MIC for vancomycin. Inhibition halos induced by vancomycin-impregnated paper diskettes were slightly larger than those by teicoplanin. Glycopeptide resistance among methicillin-resistant Staphylococcus aureus in Italy is an underestimated phenomenon, possibly due to the described underestimation of glycopeptides MICs by the automatic broth microdilution method, when compared to agar MIC assays. A teicoplanin MIC creep, as reported for vancomycin, cannot be assumed.