Thèse de doctorat en Microbiologie
Sous la direction de Carlos Rosa et de Yves Le Loir.
Soutenue en 2009
Staphylococcus aureus is an important pathogen in domestic ruminants, an agent of food poisoning and is considered as an indicateur of hygienic-sanitary quality of foodstuffs like cheese. The objectives of this study were to verify if the genetic homogeneity of S. Aureus isolates was associated to the hosts of origin (bovine, ovine and caprine) or to the site of colonization/infection (nares and udder) and if the agr (accessory gene regulator) group and cap (capsular) type of these isolates were correlated with a given host or with the locus of isolation. The resistance profile of these isolates to oxacillin and to the most commnly used antibiotics in the treatment of mastitis in ruminants also was studied. Moreover, the objectives of this work were to determine the possible S. Aureus contamination sources involved in the Minas Canastra cheese productin and the persistence of the contaminating strains during the process. By pulsed-field gel electrophoresis, 7 major clusters were identified amoung 153 isolates recovered from different geographic regions and years of isolation. Typing of agr and cap serotype was carried out on all the isolates and revealed the predominance of agrI and of cap8 regardless the ruminant host species. Antimicrobial susceptibility testing revealed resistance to ampicillin in 34 % of strains. A very low prevalence of resistance was found for the other antimicrobial agents tested (kanamycin, tetracycline and oxacillin).