Caratterizzazione diStaphylococcus aureusisolato da formaggi ovini al latte crudo e profilo di antibiotico resistenza

In vitro activities of 16 antibiotics were tested against 100S. aureus(SA) isolated from raw sheep’s milk curds taken from 10 factories. The Minimum Inhibitory Concentration (MICs) of 16 antibiotics was determined by the broth microdilution method. All 100 isolates were analyzed to detect accessory gene regulatoragr(I-IV) and genes encoding resistance for methicillin (mecA), erythromycin (ermA), penicillin (blaZ) and vancomycin (vanA-B). All the strains were also analyzed to detect the presence of several genes, encoding corresponding virulence factors, by multiplex Polymerase Chain Reaction (PCR). Samples with Coagulase Positive Staphyloccoci (CPS) concentration ≥105cfu/g, were tested for SEs (A-D) production, in compliance with Reg. CE 2073/2005, using Reversed Passive Latex Agglutination (RPLA) kit. The isolates were also analyzed to investigate Pulsed-field Gel Electrophoresis (PFGE) type diversity.SAstrains showed resistance to Ampicillin (20.0%), Penicillin (19.0%), Tetracycline (6.0%) and Cloxacillin (1.0%), whereas they were susceptible (74.0%) to 12 out of 16 tested antimicrobial agents. The strains resulted resistant to the tested antibiotics harbored the correspondent encoding genes. The overall susceptibility of the strains to Oxacillin, Vancomycin and Erythromycin was confirmed by the absence of themecA, vanA-BandermA. The PFGE showed that 94 strains belonged to 35 different clusters (C1-C35) while 6 were untypable.