Isolation and significance of anaerobic bacteria isolated from cases of bovine mastitis.

The role of obligate anaerobic bacteria in the aetiology of mastitis of lactating dairy cows was investigated. Anaerobes were isolated from 12% of lactating mastitic cows, which were representative of 50% of the 10 dairy herds examined. Bacteroides fragilis was the most frequently isolated organism of (50%), followed by Peptococcus indolicus (33%), Eubacterium lentum (33%), E. aerofaciens (17%), Propionibacterium granulosum (17%) and an anaerobic Streptococcus sp. (17%). These obligate anaerobes were always isolated together with organisms classically involved in mastitis. It was possible to induce overt clinical mastitis in healthy lactating udders within 24 hours by infection with single pure cultures of anaerobes via the teat canal. All B. fragilis strains were resistant to penicillin G and tetracycline. In addition, one strain was also resistant to ampicillin, cephalothin and amoxicillin. Anaerobic gram positive cocci and bacilli were sensitive to most antibiotics. These findings imply an important role for anaerobes in the aetiology of mastitis.