Some features of coagulase positive staphylococci from bovine milk. 1. Carbohydrate metabolism: comparison of conventional techniques and the API 50 CH system.

When conventional techniques were applied to 84 isolates of Staphylococcus aureus from milk samples, it was found that they were all catalase and phosphatase positive and oxidase negative. They all fermented glucose within 24 h and mannitol within 24-48 h when inoculated into Hugh & Leifson's medium, enriched with 1% horse serum. When they were subjected to the carbohydrates of the API 50 CH system, all metabolized glucose aerobically, but only 85-89% of the isolates could utilize mannitol aerobically. Because of the difference in the utilization of mannitol observed, the value of the API 50 CH classification in the taxonomy of S. aureus becomes questionable. This system could be used as a handy tool, however, when selecting carbohydrates to be used in taxonomical studies.