LECITHINASE REACTION OF STAPHYLOCOCCUS-AUREUS STRAINS OF DIFFERENT ORIGIN ON BAIRD-PARKER MEDIUM

Staphylococcus aureus produces one or more enzymes with lipolytic acti vity, but differences between strains have been reported (Owens and Jo hn 1975; O'Toole 1987; Rollof et al. 1987). The biological and biochem ical properties of these enzymes have been investigated and results we re recently reviewed (Kotting et al. 1984). Baird-Parker medium (Baird -Parker 1962) is a selective medium commonly used for the isolation of Staph. aureus. The presence of egg yolk in this medium permits the de tection of two reactions due to lipolytic activity of staphylococci : (1) Lecithinase reaction, a zone of precipitate in the medium surround ing the colonies; and (2) Lipase reaction or 'pearly layer', an irides cent film in and immediately surrounding colonies, visible by reflecte d light (iridescent sheen or 'oil in water'). In this study, human and bovine strains, previously biotyped according to the scheme of Devrie se et al. (1984), were compared for production of a zone of precipitat ion, lecithinase reaction, on Baird-Parker medium. Bovine and human st rains of Staph. aureus were compared for production of the egg yolk re action (lecithinase reaction) on Baird-Parker medium and the results w ere related to their biotypes and site of origin of the sample. Human strains and strains biotyped as human biotypes had higher percentage o f positive results than bovine isolates and/or biotypes. However, all strains isolated from body sites of heifers produced a positive reacti on regardless of the biotype.