STRAIN DIFFERENTIATION OF ISOLATES OF STREPTOCOCCI FROM BOVINE MASTITIS BY PULSED-FIELD GEL-ELECTROPHORESIS

Pulsed-field gel electrophoresis (PFGE) was examined as a tool to diff erentiate strains of streptococci isolated from clinical and sub-clini cal cases of bovine mastitis. Analysis of SmaI chromosomal digests of Streptococcus agalactiae, S. dysgalactiae subsp. dysgalactiae and S. u beris isolates revealed intraherd and interherd strain relationships w ithin each species. Comparison of S. agalactiae isolates from the same herd revealed little variability in their SmaI restriction patterns i ndicating a single strain originating from a common source of infectio n. However, comparison of S. agalactiae isolates between herds showed that each herd was infected with a distinct strain. The restriction pr ofiles from S. dysgalactiae subsp. dysgalactiae and S. uberis were mor e diverse and often multiple strains of both species were present with in an individual herd, with some herds containing more than one repres entative of a particular strain. Interestingly, it was only observed w ith S. dysgalactiae subsp. dysgalactiae that some strains were present in more than one herd. PFGE was found to be a useful and reproducible method for the discrimination of different strains of the three most important species of streptococci responsible for bovine mastitis and to offer a means to identify environmental sources of infection. (C) 1 997 Academic Press Limited.