Variation in Counts, Enterotoxin Levels and TNase in Swiss-Type Cheese Contaminated with Staphylococcus aureus

Area of Science:

• Food Science
• Microbiology
• Public Health

Background:

• Staphylococcal intoxications linked to contaminated Swiss-type cheese in 1977.
• Investigation prompted by multiple recalls of cheese manufactured in early 1977.

Purpose of the Study:

• To quantify Staphylococcus aureus contamination in recalled Swiss-type cheese.
• To detect staphylococcal thermonuclease (TNase) and enterotoxin levels.
• To assess pH variations and their potential impact on cheese safety.

Main Methods:

• Analysis of 59 cheese lots for S. aureus counts, TNase, enterotoxin B, and pH.
• Sampling from various locations within cheese blocks (center and periphery).

Main Results:

• S. aureus counts ranged from <25 to 10^8 CFU/g, with most between 10^4-10^6 CFU/g.
• Enterotoxin B detected in 72.6% of samples; TNase in 52.5%.
• pH levels varied (5.5-6.2), often exceeding the normal range for Swiss-type cheese (5.7).
• Significant variations observed within and between cheese lots and blocks.

Conclusions:

• Contaminated cheese posed a significant health risk due to high bacterial loads and toxin presence.
• Variations in starter cultures, processing temperatures, and salt penetration may explain contamination inconsistencies.
• Recommend sampling both center and periphery of cheese blocks for comprehensive analysis of S. aureus, TNase, and enterotoxin.