Staphylococcus aureus as source of catheter-related bloodstream infection evaluated by PFGE and rep-PCR typing in a Brazilian hospital.

Staphylococci are a common cause of catheter-related bloodstream infection (CR-BSI), and epidemiological typing is an important tool for effective infection control. This study evaluated by PFGE and rep-PCR whether Staphylococcus aureus strains isolated from skin and catheter tips were related to specimens isolated from blood. A prospective observational study, carried out in a clinical surgical ward at a Brazilian hospital between September 2000 and November 2002, investigated non-tunneled central venous catheters from 179 patients. S. aureus isolates were mainly obtained from blood (41.4%), while coagulase-negative staphylococci strains were more often isolated from the skin at the catheter insertion site (49.7%) and from the catheter tip (57.5%). Among the 21 strains isolated from 9 patients at 2 or 3 sites simultaneously, 9 were methicillin-resistant S. aureus (MRSA) and 12 were methicillin-susceptible S. aureus (MSSA). Seven patients harbored the same S. aureus strain isolated from the skin, blood and/or catheter tip cultures. MRSA isolates belonged to one PFGE pattern (type A- subtypes A(1), A(2) and A(3)), and to two rep-PCR patterns (a and b). MSSA isolates were distinguished in five PFGE (B to F) and in three rep-PCR (c, d and e) patterns. Both PFGE and rep-PCR methods indicated that the skin at the catheter insertion site was the origin of CR-BSI caused by S. aureus.

Simplified and reliable scheme for species-level identification of Staphylococcus clinical isolates.

Reliable and rapid identification of staphylococcal strains continues to be a problem faced by many microbiology laboratories. This study evaluates a simplified method that uses a flowchart to assist in the identification of 12 clinical species of Staphylococcus, including eight subspecies. A total of 198 isolates and 11 control strains were identified by the reference method, which employed 22 tests. The results were compared with those obtained by two other methods: an automated system (MicroScan WalkAway) and a simplified method composed of nine tests. The simplified scheme showed an accuracy of 98.5%, while the automated method showed an accuracy of 79.3% (P < 0.001), in identifying staphylococcal species. Atypical phenotypic profiles were detected by both the reference (55.6%) and the simplified (19.7%) methods. The simplified method proposed here was shown to be reliable, with the advantage of being more practical and economic than the reference method.