Phenotypic and Molecular Typing of Nosocomial Methicillin-Resistant Staphylococcus aureus Strains Susceptible to Gentamicin Isolated in France from 1995 to 1997

摘要

Methicillin-resistant strains susceptible to gentamicin (Gm^s MRSA) have emerged since 1993 in several French hospitals. To study whether particular clones have spread in various French cities and whether some clones are related to gentamicin-resistant (Gm^r) MRSA strains, various methods (antibiotyping, phage typing, determination of SmaI macrorestriction patterns before and after hybridization with IS256 transposase and aacA-aphD probes) were used to compare 62 Gm^s MRSA strains isolated from 1995 to 1997 in nine cities and 15 Gm^r MRSA strains. Eighteen major SmaI genotypes were identified, of which 11 included only Gm^s MRSA strains and 5 included only Gm^r MRSA strains. Each of the Gm^r MRSA strains contained 6 to 13 SmaI fragments hybridizing with the insertion sequence IS256, of which a single band also hybridized with the aacA-aphD gene. No such hybridizing sequences were detected in 60 of the 62 Gm^s MRSA strains. Thus, the divergence between Gm^r and Gm^s MRSA strains is revealed, not only by their distributions in distinct SmaI genotypes but also by the differences in hybridization patterns. Two of the 62 Gm^s MRSA strains had the uncommon feature of carrying several SmaI bands hybridizing with IS256, suggesting that they are possibly related to the Gm^r MRSA strains grouped in the same SmaI genotype. Five of the 11 SmaI genotypes including only Gm^s MRSA strains contained strains from diverse cities, isolated during different years and with different antibiograms, suggesting that some clones have spread beyond their cities of origin and persisted.