Coliform Bacteria and Staphylococcus aureus in Retail Natural Cheeses

Area of Science:

• Food Microbiology
• Food Safety Analysis
• Dairy Science

Background:

• Natural cheeses are a common food source, necessitating evaluation for microbial safety.
• Previous studies indicated higher levels of certain pathogens in cheeses.
• Assessing current retail cheese safety is crucial for public health.

Purpose of the Study:

• To determine the prevalence of coliform bacteria, Escherichia coli, E. coli O157:H7, and thermonuclease-positive S. aureus in commercial natural cheeses.
• To compare current contamination levels with historical data.
• To assess the microbiological safety of retail natural cheese products.

Main Methods:

• Fifty commercial retail samples of natural cheeses were analyzed.
• Microbiological analysis included violet red bile agar and enrichment broth methods.
• Specific target organisms were coliform bacteria, E. coli, E. coli O157:H7, and S. aureus.

Main Results:

• Coliform bacteria were detected in 9 samples (18%) by violet red bile agar, with counts up to 1.1 × 10^3 CFU/ml.
• 48% of cheeses tested positive for coliforms using a 25-g enrichment broth method.
• One sample confirmed E. coli; no E. coli O157:H7 or thermonuclease-positive S. aureus were isolated.
• Detected pathogen levels were lower than those reported in a 1974-1976 Canadian study.

Conclusions:

• Retail natural cheeses generally show low levels of the tested pathogenic bacteria.
• The microbiological safety of natural cheeses appears to have improved compared to previous decades.
• Continued monitoring is recommended to ensure ongoing food safety standards.