Incidence of Staphylococcus aureus with reduced susceptibility to glycopeptides in two French hospitals.

OBJECTIVES: To determine the incidence of Staphylococcus aureus isolates with reduced susceptibility to glycopeptides among all clinical isolates collected consecutively in two French hospitals between November 1998 and April 1999. METHODS: Methicillin-resistant and -susceptible S. aureus isolates were screened on vancomycin- or teicoplanin-supplemented agar plates. Glycopeptide MICs were determined by the E test procedure with a high inoculum and by an agar dilution technique. Glycopeptide-intermediate S. aureus isolates were identified as homogeneously or heterogeneously resistant to vancomycin by performing population analysis. RESULTS: Of the 640 isolates recovered from 518 patients, three from the same patient and two from two different patients showed homogeneous or heterogeneous intermediate resistance to vancomycin. CONCLUSION: The incidence of glycopeptide-intermediate S. aureus (homogeneously or heterogeneously resistant) in a non-selected patient population, i.e. regardless of predisposing factors and glycopeptide therapeutics, remains low in the two French hospitals involved in the study, representing 0.6% of isolates.

Clinical isolate of vancomycin-heterointermediate Staphylococcus aureus susceptible to methicillin and in vitro selection of a vancomycin-resistant derivative.

A Staphylococcus aureus strain with low-level heteroresistance to vancomycin (designated MER) but susceptible to methicillin was isolated from an outpatient with conjunctivitis who did not receive any glycopeptide antibiotics. Incubation of the parent strain, MER, with increasing concentrations of vancomycin led to rapid selection of a stable progeny homogeneously resistant to vancomycin. Electron micrographs of strain MER showed enhanced cell wall thickness and abnormal septations typically seen with methicillin-resistant S. aureus having intermediate susceptibility to vancomycin.