Methicillin-resistant Staphylococcus aureus (MRSA) from bovine milk samples [Staphylococcus aureus meticillino-resistenti (MRSA) da campioni di latte bovino].

Aim: Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important hospital and community-acquired pathogen. MRSA are also reported in farm animal and more recently reported as cause of bovine mastitis in Belgium and Germany. The aim of this study was to asses the presence of MRSA in some herds of the Po Valley and provide further characterization of the isolates. Results: between October 2008 and February 2010, 2875 strains of S. aureus were isolated from different herds. A sample of 425 strains, representative of different farms of origin, were tested for methicillin-resistance by oxacillin agar diffusion test and mecA gene PCR. 55 MRSA strains were isolated from 20 different dairy farms. Fourteen MRSA randomly selected, were genotyped for the presence of the main recognized virulence factors and characterized by spa-typing, MLST and SCCmec typing. The characterization of the MRSA strains showed higher frequency of ST398, t899 spa-typing, the typical profile of livestock-associated MRSA (LA-MRSA). A strain was belonging to genotype t355, ST152, associated with human infections. Four MRSA were enterotoxigenic. Conclusions: MRSA are present in several cattle herds in the Po Valley and may represent a reservoir of infection for humans, in particular for those involved in animal husbandry, and a food-borne risk through the contamination of the food chain. Management of contagious MRSA mastitis should consider strict control measures and eradication among effective options.