Differentiation of Strains of Staphylococcus epidermidis Isolated From Bovine Udders

Strains of Staphylococcus epidermidis isolated from bovine udders were differentiated by comparing biochemical tests, serological typing of proteolytic enzymes, colonial morphology, and the spectrophotometric analysis of pigments extracted with methanol. The cultures were divided into proteinase-positive and proteinase-negative groups, based on their proteolytic activity on skim milk agar, staphylococcus medium no. 110 (Difco), and gelatin. Most of the proteinase-negative cultures produced acetoin, whereas the opposite was true for the proteinase-positive cultures. A further subdivision of the cultures in each group was made by using Baird-Parker's (1963) biochemical subgrouping scheme. The proteinase-positive cultures were also subdivided by serological typing of their proteolytic enzymes into five groups, B, F, G, H, and NR, a non-reacting group. Approximately three-quarters of the cultures in the first four proteinase groups could be placed in one of Baird-Parker's biochemical subgroups. The cultures in the NR group, however, were sufficiently distinctive in their biochemical reactions to be considered as a separate biochemical subgroup. The colonies formed by the cultures were classified into five types, each consisting of two to four forms. No absolute relationship was found between the spectral absorption curves of the pigments and proteinase groups, although there were differences in the types of absorption curves that predominated in each proteinase group. Nine cultures which produced coagulase were more closely related to S. epidermidis than to S. aureus in that they did not utilize mannitol anaerobically or produce α-or β-type haemolysis, they were non-pigmented and were less active biochemically. Also, serological typing of the proteolytic enzymes of three of these cultures resulted in one being classified as group G and two as group H. Group H contained only these two cultures. In contrast 27 cultures of S. aureus were classified as group A. Except for coagulase production, the biochemical reactions and the serological grouping of the proteolytic enzymes suggested a classification of S. epidermidis for the nine cultures.