Molecular epidemiology and antimicrobial susceptibility testing. Testing of quinolone-resistant Staphylococcus aureus...

An outbreak of 20 oxacillin-resistant Staphylococcus aureus (ORSA) bloodstream infections (BSIs) was detected in the intensive care unit (ICU) at Hospital Sao Paulo, Brazil. In a surveillance study, 10% of ICU personnel were defined as chronic nasal carriers of ORSA. Thirteen BSIs and five nasal isolates were available for phage typing, restriction endonuclease analysis of plasmid (REAP) and chromosomal DNA hybridized with 32P rRNA gene probe. Susceptibility testing against select antimicrobial agents, including 11 quinolones, six glycopeptides, and five topical agents, was performed by broth microdilution and the disk diffusion tests. Ten of the 13 BSI isolates and four of the five nasal strains were oxacillin and quinolone resistant. The new fluoroquinolones CI-960 and WIN57273, the glycopeptides, and the topical agents ramoplanin, bacitracin, mupirocin, and novobiocin were most active. Fourteen strains, 12 BSI isolates, and three nasal isolates showed the same REAP profile. Moreover, the same REAP and chromosomal profile was detected in at least nine BSI isolates and in two nasal isolates. These strains were nontypable by phage typing. We concluded that nosocomial cross-transmission of a single, multiresistant strain of S. aureus occurred and that the epidemic reservoir was nasal carriage by ICU personnel.