Lecithinase reaction of Staphylococcus aureus strains of different origin on Baird-Parker medium.

Staphylococcus aureus produces one or more enzymes with lipolytic activity, but differences between strains have been reported (Owens and John 1975; O'Toole 1987; Rollof et al. 1987). The biological and biochemical properties of these enzymes have been investigated and results were recently reviewed (Kötting 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 detection of two reactions due to lipolytic activity of staphylococci: (1) Lecithinase reaction, a zone of precipitate in the medium surrounding the colonies; and (2) Lipase reaction or 'pearly layer', an iridescent film in and immediately surrounding colonies, visible by reflected light (iridescent sheen or 'oil in water'). In this study, human and bovine strains, previously biotyped according to the scheme of Devriese et al. (1984), were compared for production of a zone of precipitation, lecithinase reaction, on Baird-Parker medium. Bovine and human strains of Staph. aureus were compared for production of the egg yolk reaction (lecithinase reaction) on Baird-Parker medium and the results were related to their biotypes and site of origin of the sample. Human strains and strains biotyped as human biotypes had higher percentage of positive results than bovine isolates and/or biotypes. However, all strains isolated from body sites of heifers produced a positive reaction regardless of the biotype.