Evaluation of an improved MPN medium for recovery of stressed and nonstressed Staphylococcus aureus

Area of Science:

• Food Microbiology
• Bacteriology
• Food Safety

Background:

• Staphylococcus aureus is a significant foodborne pathogen.
• Accurate recovery methods are crucial for food safety monitoring.
• Existing methods like trypticase soy broth with 10% salt (TSBS) may have limitations in recovering stressed or low-level bacterial populations.

Purpose of the Study:

• To compare the efficacy of two culture media for recovering foodborne Staphylococcus aureus.
• To evaluate the impact of adding sodium pyruvate to a standard recovery medium.

Main Methods:

• Comparison of trypticase soy broth with 10% salt (TSBS) and TSBS with 1% sodium pyruvate (PTSB).
• Recovery trials using artificially contaminated mashed potato and ham salad with heat-stressed and nonstressed S. aureus strains.
• Analysis of S. aureus recovery from naturally contaminated Monterey Jack cheese.

Main Results:

• The addition of sodium pyruvate (PTSB) significantly increased the recovery of S. aureus from artificially contaminated food matrices.
• PTSB demonstrated higher overall geometric means for S. aureus recovery compared to TSBS.
• Recovery of S. aureus from naturally contaminated cheese was significantly higher in PTSB (96/g) than in TSBS (63/g).

Conclusions:

• Supplementing TSBS with 1% sodium pyruvate (PTSB) enhances the recovery of foodborne Staphylococcus aureus.
• PTSB is a more effective medium for detecting S. aureus in various food types, including cheese.
• This improved recovery method can contribute to more accurate food safety assessments.