Cossu, Francesca (2010) Caratterizzazione di Staphylococcus aureus isolato da formaggi ovini al latte crudo e profilo di antibiotico resistenza. Doctoral Thesis.
In vitro activities of 16 antibiotics were tested against 100 S. 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 regulator agr (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 ≥105 cfu/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. SA strains 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 the mecA, vanA-B and ermA. The PFGE showed that 94 strains belonged to 35 different clusters (C1-C35) while 6 were untypable.
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