title: Characterization of gentamicin-susceptible strains of methicillin-resistant Staphylococcus aureus involved in nosocomial spread.
abstract: We report an outbreak of epidemic Staphylococcus aureus strains characterized by an unusual heterogeneous resistance to methicillin and resistance to tobramycin but susceptibility to gentamicin (gentamicin-susceptible methicillin-resistant S. aureus [GS-MRSA]), contrasting with gentamicin-resistant homogeneous MRSA (GR-MRSA) that have been endemic in our hospital since the 1970s. A total of 97 GS-MRSA strains, which were shown by DNA hybridization to carry the mecA and ant(4')-Ia genes, were studied. The 40 GS-MRSA strains isolated at the beginning of the outbreak (January 1992 to June 1993) were typed by using resistance patterns, phage typing, serotyping, and pulsed-field gel electrophoresis and were compared with GR-MRSA and methicillin-susceptible S. aureus (MSSA) strains isolated during the same period. Two dominant clones, A::1 and B::3, and one minor clone, C::5, were identified among the 40 GS-MRSA strains, according to pulsotypes (A to C) and their resistance patterns (1, 3, and 5), which were distinguishable from those of GR-MRSA and MSSA strains. A selection of 57 GS-MRSA strains, isolated from 1994 to 1996, were clustered in the same three clones. However, their distribution had changed in comparison with that in the 1992 to 1993 period: clone A::1 remained dominant (47 versus 42.5%), whereas clone B::3 progressively declined (5 versus 35%) and clone C::5, the most susceptible to antibiotics, spread (44 versus 2.5%). Epidemiological investigations revealed that some clones had been introduced via patients transferred from other hospitals and that cross-infection occurred within and between wards. Major changes in the use of antibiotics, especially aminoglycosides, cyclines, and macrolides, likely played a role in the emergence and spread of GS-MRSA strains.
authors.affiliation: Laboratoire de Bactériologie-Hygiène, Groupe Hospitalier Pitié-Salpêtrière, Paris, France. sougakof@lmcp.jusssieu.fr
authors.forename: N
authors.initials: N
authors.lastname: Lemaître
authors.forename: W
authors.initials: W
authors.lastname: Sougakoff
authors.forename: A
authors.initials: A
authors.lastname: Masmoudi
authors.forename: M H
authors.initials: MH
authors.lastname: Fievet
authors.forename: R
authors.initials: R
authors.lastname: Bismuth
authors.forename: V
authors.initials: V
authors.lastname: Jarlier
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003428:Cross Infection / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology*; D004196:Disease Outbreaks; D005838:Genotype; D005839:Gentamicins / Q000494:pharmacology*; D006801:Humans; D016106:Methicillin Resistance; D010641:Phenotype; D013211:Staphylococcus aureus / Q000145:classification* / Q000187:drug effects / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D005839:Gentamicins