Investigation of an outbreak caused by methicillin-resistant Staphylococcus aureus in a cardiovascular surgery unit by ribotyping, randomly amplifed polymorphic DNA and pulsed-field gel electrophoresis

An outbreak caused by rapid spread of methicillin-resistant Staphylococcus aureus (MRSA) in an intensive care unit for cardiovascular surgery was inve stigated by phenotypic and genotypic methods. Fourteen isolates were collec ted during a 2-month period from clinical and environmental specimens in th e unit recently re-opened after reconstruction. The isolates were tested fo r antibiotic susceptibility patterns and genotyped by automated ribotyping, randomly amplified polymorphic DNA-PCR (RAPD) analysis and pulsed-field ge l electrophoresis (PFGE). Automated ribotyping applying EcoRI digestion pro ved to be of no value in separating the isolates. In contrast, PFGE grouped the isolates into four clusters different from the reference strain. These results fully correlated with the antibiograms. Twelve of the isolates wer e grouped into two clonally related clusters. RAPD analyses grouped the iso lates into five clusters. Except for two isolates of one patient, which had different RAPD patterns, PFGE and RAPD analyses presented very similar res ults. The results verified the usefulness of PFGE in studies of MRSA epidem ics. A combination of these two methods reduces the time to identification of an outbreak and increases the accuracy in detection of intraspecies diff erences.