Outbreak of subclinical mastitis due to beta hemolytic group L streptococci (S. dysgalactiae ssp. equisimilis) in an Austrian dairy herd

This study is reporting an outbreak of subclinical mastitis due to beta-hemolytic group L streptococci in an Austrian dairy herd with a history of high somatic cell count. At the first survey 16 of 33 lactating cows (28 quarters of 132) were cultured positive for beta-hemolytic, CAMP and esculin negative cocci that grew on Columbia blood agar with small grey catalase negative colonies. With the commercial API 20 Strep system (bioMerieux, F) isolates were classified as members of streptococci group L. All tested strains (eight of 28) produced acid from ribose, lactose, trehalose, amidon and glycogen; they hydrolysed hippurate and showed beta-glucuronidase, beta-galactosidase, alkaline phosphatase, leucinaminopeptidase and arginindehydrolase activity. Isolates were sensitive to bacitracin but resistant to tetracycline. Using phenotypic characterisation as well as sequence analysis of the 16S-23S intergenic spacer region of a representative strain, recovered isolates were identified as Streptococcus (S.) dysgalactiae ssp. equisimilis. Mastitis was characterized by normal milk secretions and absence of clinical abnormalities but high elevations of somatic cell count. Based on the characteristics of the strains and on the observations during the first herd survey, contagious transmission during milking as a result of poor milking hygiene was assumed. The mastitis was controlled through implementation of a strict hygiene protocol including use of single-use udder towels, post milking teat desinfection and cluster disinfection between milking cows in combination with antibiotic treatment of infected udders.