3M™ Petrifilm™ Staph Express Count plate method for the enumeration of Staphylococcus aureus in selected dairy foods:: Collaborative study

The 3M(TM) Petrifilm(TM) Staph Express Count plate method was compared with AOAC Official Method 975.55 for the enumeration of Staphylococcus aureus in selected foods. Five foods-ice cream, raw milk, yogurt, whey powder, and cheese-were analyzed for S. aureus by 12 collaborating laboratories. For each food tested, the collaborators received 8 blind test samples consisting of a control sample, a low inoculation level, a medium inoculation level, and a medium inoculation level with background flora, each in duplicate. The mean log(10) counts for the methods were comparable for all 5 foods. The repeatability and reproducibility variances of the 24 h Petrifilm Staph Express Count plate method were similar to those of the 72 h standard method.