The role of teat skin contamination in the epidemiology of Staphylococcus aureus intramammary infections Renata Piccinini 1 , Lorenza Cesaris 1 , Valentina Dapra ` 1 , Vitaliano Borromeo 1 , Claudia Picozzi 2 , Camillo Secchi 1 & Alfonso Zecconi 1 * 1 Dept. of Animal Pathology, Hygiene and Public Health. Universita ` degli Studi di Milano, Via Celoria 10, 20133 Milano, Italy 2 Dept. Food Science and Technology. Universita ` degli Studi di Milano, via Celoria 2, 20133 Milano Received 17 April 2008; accepted for publication 21 July 2008 ; first published online 16 October 2008 Knowledge of the epidemiological pattern and the potential sources of infections is important to control Staphylococcus aureus in dairy herds. This paper reports the results of a study applying both pulse field gel electrophoresis (PGFE) and the assessment of a selected number of virulence genes to investigate the role of teat skin on Staph. aureus transmission among cows and on the contamination of milk. Overall 61 isolates were considered, 23 from teat skin, 33 from milk samples and 5 from curd samples. Teat swabs were taken in five herds, but in only three of them could Staph. aureus be isolated. Curd was sampled in three herds, but Staph. aureus could be isolated in only two herds. The distribution of isolates among herds confirmed the presence of herd-specific Staph. aureus strain in most of the herds. The same pattern was observed in teat skin samples, in quarter milk samples, and in the curd samples. Our findings are consistent with other studies showing the role of teat skin as a potential reservoir. Moreover, Staph. aureus was isolated from teat skin of confirmed Staph. aureus-negative cows that were segregated from infected ones. Our findings also suggest that some strains have higher chances to survive on teat skin and therefore to increase the risk for contamination of milk and milk products due to the persistence of intramammary infections. Keywords : Staphylococcus aureus, intramammary infections, teat skin, molecular epidemiology, PFGE. Staphylococcus aureus is recognized as the major con- tagious mastitis pathogen worldwide (Zecconi et al. 2006a). Moreover, Staph. aureus is associated with both human and foodborne diseases (Balaban & Rasooly, 2000 ; Honeyman et al. 2001). The large number of diseases caused in different species can be related to the vast array of virulence factors expressed by Staph. aureus and by the ability to colonize different sites both on the body (skin, nares, udder) and can be found also in devices such as prosthesis and milking machines (Roberson et al. 1994 ; Montanaro et al. 1999). To control the disease at herd level and to reduce the risk of milk contamination with Staph. aureus enterotoxin it is important to identify the epidemiological pattern and hence the sources of infection and contamination (Zecconi et al. 2006a; Andre et al. 2008). These kinds of epidemiological studies currently rely on molecular characterization of iso- lates. Several molecular methods have been proposed to characterize Staph. aureus, or to identify virulence patterns (Matthews et al. 1994 ; Aarestrup et al. 1995 ; Fitzgerald et al. 1997 ; Rivas et al. 1997 ; Zecconi et al. 2005 ; Zecconi et al. 2006b) in isolates from dairy cows. Among all these meth- ods pulsed field gel electrophoresis (PFGE) is recommended for Staph. aureus typing (Tenover et al. 1994; McDougal et al. 2003) but it discriminates the different isolates without giving information on the presence of the different virulence factors. Such problems could be overcome by combining PFGE with a validated method to identify virulence gene pattern (Zecconi et al. 2005 ; Zecconi et al. 2006b). This paper reports the results of a study applying both PFGE and the assessment of the presence of a selected number of virulence genes to investigate the potential role of teat skin on Staph. aureus transmission among cows and on the source of contamination of milk and milk products. Material and Methods Herds and sampling Nine herds following a mastitis control programme based on segregation of infected cows as described in previous *For correspondence ; e-mail : alfonso.zecconi@unimi.it Journal of Dairy Research (2009) 76 36–41. f Proprietors of Journal of Dairy Research 2008 36 doi:10.1017/S0022029908003671 Printed in the United Kingdom