Retrospective screening for heterogeneous vancomycin resistance in diverse Staphylococcus aureus clones disseminated in French hospitals

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Abstract
Twenty-five different Staphylococcus aureus strains that are widespread in France were screened by various methods for heterogeneous and low-level resistance to vancomycin. Population analysis on brain–heart infusion agar containing 4 mg/L of the drug detected resistant cells at frequencies of 10–7 to 10–6 in five multiply resistant strains. There was no antagonism between vancomycin and β-lactam antibiotics. One of the five strains, isolated in 1993, was considered a putative progenitor of a French nosocomial S. aureus strain isolated in 1998 and for which the vancomycin MIC was 8 mg/L.