FREQUENCY, CLONAL HETEROGENEITY AND ANTIBIOTIC-RESISTANCE OF METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS (MRSA) ISOLATED IN 1392-1394

Since 1992, the proportion of methicillin-resistant Staphylococcus aur eus (MRSA) isolated from patients of the University Hospital of Frankf urt/Main and six community hospitals increased to a level of 11% and h as remained constant during the following two years. MRSA and methicil lin-sensitive Staphylococcus aureus (MSSA) were distributed equally am ong almost all specimens except blood. There was evidence of a diminis hed potency of MRSA to cause bacteremia. All MRSA strains were suscept ible to glycopeptides and mupirocin. Resistance rates to other non-bet a-lactam antibiotics were low for fusidic acid (7.1%), fosfocin (8.3%) , amikacin (11.4%) and cotrimoxazole (18.3%) and high for gentamicin ( 90.7%), ofloxacin (94.3%) and erythromycin (95.5%). Among 378 MRSA str ains originating from 180 individuals, macrorestriction analysis of ch romosomal DNA revealed 39 different genotypes. These could be divided into 14 epidemic strains isolated from 155 patients and 25 sporadic st rains isolated from single patients. As most of the sporadic strains e merged in close local proximity to epidemic strains, we suppose a hori zontal genetic transfer from MRSA to MSSA leading to the appearance of novel MRSA genotypes. Upon repeated isolation of MRSA strains from th e same individuals, resistance rates and genotypes remained stable. Re sistance patterns of the non-beta-lactams correlated poorly with macro restriction analysis, whereas several MRSA genotypes could be distingu ished by particular MICs of methicillin.