The role of anaerobic bacteria in bovine mastitis: a review.

Routine bacteriological diagnosis of bovine mastitis does not provide an index to the obligate anaerobic flora involved. No anaerobic bacteria were recovered from cows with normal quarters or those with latent facultative anaerobic or aerobic udder infections as diagnosed according to the criteria of the International Dairy Federation. Simultaneous isolation of anaerobic bacteria from udder quarter abscesses and mastitic milk from the same quarter occur in some lactating dairy cows. In most dairy herds there are cows with anaerobic udder infections. Anaerobic bacteria have been isolated from lactating as well as from dry cows. Most anaerobic bacteria were isolated concurrently with facultative anaerobic bacteria except in aseptic mastitis cases. The polymicrobial nature of udder infections shows that multiple anaerobic as well as facultative anaerobic species colonise and act together. In spite of antibiotic therapy, anaerobic bacteria were still isolated from mastitic quarters. Gram-positive anaerobic bacteria were mostly sensitive to penicillin-G but most of the Gram-negative anaerobic bacteria were resistant and some Bacteroides fragilis strains produced beta-lactamase. Nearly all the aminoglycosides display consistently poor activity against anaerobic bacteria. A high degree of resistance against tetracyclines was also demonstrated. Anaerobic Gram-positive cocci and rods were sensitive to common antibiotics. The pathogenicity of several pure cultures of anaerobic bacteria has been demonstrated by their ability to induce clinical mastitis in healthy lactating udders. Anaerobic bacteria may act as mastitis pathogens probably in a primary and/or secondary role because clinical mastitis could be induced in normal quarters under experimental conditions. Their high prevalence of anaerobic bacteria in mastitic quarters and the ability of some strains to produce heparinase also suggests a pathogenic role. The handling of udder abscesses and the therapy of mastitis where anaerobic bacteria may be involved, is fully discussed.