Performance of Four Selective Media for Enumerating Staphylococcus aureus in Corned Beef and in Cheese

Area of Science:

• Microbiology
• Food Safety
• Bacteriology

Background:

• Accurate enumeration of Staphylococcus aureus is crucial for food safety.
• Selective media are commonly used for isolating and quantifying S. aureus in food products.
• Different strains of S. aureus may exhibit varying growth characteristics on selective media.

Purpose of the Study:

• To evaluate the performance of four selective media for enumerating Staphylococcus aureus.
• To determine if media performance is dependent on the specific strain of S. aureus or the food matrix.

Main Methods:

• Artificially contaminated corned beef and naturally contaminated cheese samples were used.
• Four selective media were tested: Baird-Parker (BP), Kranep (KR), Mannitol Salt (MS), and Staphylococcus medium 110 (S110).
• Enumeration of S. aureus was performed using these media.

Main Results:

• Media performance was strain-dependent for artificially contaminated corned beef.
• BP, KR, MS, and S110 performed equally for an enterotoxin A producing strain.
• KR and BP significantly outperformed S110 for an enterotoxin D producing strain.
• BP performed significantly better than the other three media in naturally contaminated cheese samples with high microbial competition.

Conclusions:

• The choice of selective medium for S. aureus enumeration should consider the specific bacterial strain and the complexity of the food matrix.
• Baird-Parker agar demonstrates superior performance in challenging food samples like cheese.
• Further research may be needed to optimize media for specific S. aureus strains and food types.