PHENOTYPIC AND GENOTYPIC CHARACTERIZATION OF NOSOCOMIAL STAPHYLOCOCCUS-AUREUS ISOLATES FROM TRAUMA PATIENTS

Staphylococcus aureus is a major cause of nosocomial infections, Durin g the period from March 1992 to March 1994, the patients admitted to t he intensive care unit of the University of Maryland Shock Trauma Cent er were monitored for the development of S. aureus infections, Among t he 776 patients eligible for the study, 60 (7.7%) patients developed 6 5 incidents of nosocomial S. aureus infections, Of the clinical isolat es, 43.1% possessed a polysaccharide type 5 capsule, 44.6% possessed a type 8 capsule, and the remaining 12.3% had capsules that were not ty ped by the type 5 or type 8 antibodies, Six antibiogram types were not ed among the infection-related isolates, with the majority of the type s being resistant only to penicillin and ampicillin. It was noted that the majority of cases of pneumonia mere caused by relatively suscepti ble strains, while resistant strains were isolated from patients,vith bacteremia and other infections, Only 16 (6.3%) of the isolates were f ound to be methicillin resistant S. aureus (MRSA). DNA fingerprinting by pulsed-field gel electrophoresis showed 36 different patterns, with characteristic patterns being found for MRSA strains and the strains with different capsular types, Clonal relationships were established, and the origins of the infection-related isolates in each patient were determined, We conclude that (i) nosocomial infection-related isolate s from the shock trauma patients did not belong to a single clone, alt hough the predominance of a methicillin resistant genotype was noted, (ii) most infection-related S. aureus isolates were relatively suscept ible to antibiotics, but a MRSA strain was endemic, and (iii) for prac tical purposes, the combination of the results of capsular and antibio gram typing can be used as a useful epidemiological marker.