Fomites and reservoirs of Staphylococcus aureus causing intramammary infections as determined by phage typing: the effect of milking time hygiene practices

We studied the association of milkers' hands and milking unit liners as fomites, and teat skin as a reservoir, with S. aureus intramammary infections (IMI). Samples were collected from 40 commercial herds and S. aureus isolates were phage typed. Only 10 of 257 isolates were not typable. Of the milk samples, 8.4% had typable S. aureus; 4.5% and 9.2% of the skin and liner swabbings had typable S. aureus. Twenty-three different phage types were identified, 1 type was found in nearly 75% of the herds. Herds in which milking unit backflush was used were less likely to have the same phage type on the liners and the teat skin, and on the liners and milk samples, than herds that did not backflush. A greater percentage of liners had S. aureus of the same type as those causing S. aureus IMI, than skin swabbing solutions with the same type as that associated with IMI. Herds which did not use post-milking teat asepsis (teat dip) did not have a greater percentage of S. aureus isolates on the teat skin, nor were the S. aureus test skin isolates more likely to be of the same type as those causing intramammary infection. Results would suggest that the liner appears to be a significant fomite, that backflushing reduces its significance, and that teat skin is a less significant reservoir for S. aureus intramammary infection.