Staphylococcus aureus biotypes in cows presenting subclinical mastitis from family dairy herds in the Central-Eastern State of Mexico

Mastitis causes great economic loss in dairy farms. One of the main agents involved is Staphylococcus aureus, which is important not only in public health but in herd health as well. The aim of this study was to determine S. aureus frequency and the predominant biotypes in cows presenting subclinical mastitis from family dairy farms in the Central-Eastern zone of the State of Mexico. A transversal study was conducted considering 269 dairy cows in different lactation periods and herd information was taken through a closed questionnaire. Individual milk samples were taken and California test was used for mastitis detection. Biotypes were identified using soy tripticase agar with violet cristal added (1:100,000). Results show a subclinical mastitis prevalence of 48.3 % (CI95% 42.22 to 54.47) and for clinical mastitis 6.1 % (CI95% 3.44 to 9.48). 62 S. aureus isolations were obtained, from which 79 % were biotype C (Human), 11.3 % A (Bovine), 6.5 % E (Canine) and 3.2 % from non specific hosts. Herd size represented a risk factor associated to S. aureus frequency, especially when the herd was larger than 13 cows (OR=5.63, CI95% 1.72 to 18.21). In the family dairy herds there was a high prevalence of subclinical mastitis associated to the infection produced by S. aureus Biotypes C and A, considered important in public health.