VALUTAZIONE DELLA RESISTENZA AGLI ANTIBIOTICI IN S. AUREUS ISOLATI DA FORMAGGI AL LATTE CRUDO DI PECORA

In vitro activities of 16 antibiotics were tested against 36 S. aureus (SA) isolated from raw sheep’s milk curds taken from 6 factories. The MICs of 16 antibiotics was determined by the broth microdilution method (CLSI). All 36 isolates were analyzed to detect accessory gene regulator agrI-IV and genes encoding resistance for methicillin (mecA), erythromycin (ermA), penicillin (blaZ) and vancomycin (vanA-B). The isolates were also analyzed to investigate PFGE type diversity. SA strains showed resistance to ampicillin (36.1%), penicillin (33.3%), tetracycline (11.1%) and cloxacillin (2.8%), whereas they were susceptible (94.4%) to 12 out of 16 tested antimicrobials. In the strains which were resistant according to broth microdilution method corrispondent encoding genes were usually detected. The overall susceptibility of the strains to the oxacillin, vancomycin and erythromycin is confirmed by the absence of the mecA, vanA-B and ermA. The PFGE showed that 32 strains belonged to 10 different pulsotype (P1-P10) while 4 were untypable.