Use of Baird-Parker's Medium to Enumerate Staphylococcus aureus in Meats ¹

The Staphylococcus aureus count was determined, using Baird-Parker (BP) medium and coagulase reaction, on 100 samples of ground beef, 23 frozen pork sausage samples and 140 retail meat cuts (beef and pork). S. aureus counts on ground beef ranged from < 100 to 4,500 per g, and 16% had counts of 1,000 per g or greater. Frozen pork sausage samples had similar S. aureus counts to ground beef. Retail meat cuts generally had counts less than 100 per cm². Typical S. aureus colonies in this study on BP medium were dark grey to grey-black, and not shiny black as generally described. Type II colonies (without egg yolk clearing) did not contribute markedly to the total S. aureus count and egg yolk clearing type I colony count is suggested for routine estimation of the S. aureus count. The S. aureus isolates in this study generally had 3+ coagulase reactions. The coagulase-positive isolates were generally phosphatase-positive (96.8%), Voges-Proskauer test-positive (97.4%), DNase-positive (98.7%) and used glucose and mannitol oxidatively and fermentatively (93.5%). Most non- S. aureus colonies were "other" staphylococci or micrococci. These isolates had variable phosphatase, Voges-Proskauer and DNase reactions, generally with at least one of these three tests negative.