[Recovery of Staphylococcus aureus after acid damage]

Area of Science:

• Food Microbiology
• Dairy Science
• Bacteriology

Background:

• Staphylococcus aureus is a pathogen of concern in dairy products.
• Understanding its behavior in fresh cheeses like Minas and Mozzarella is crucial for food safety.
• The impact of environmental factors, such as increasing acidity, on bacterial viability requires investigation.

Purpose of the Study:

• To examine the growth dynamics of S. aureus in Minas and Mozzarella cheeses during storage.
• To determine if increasing acidity during cheese shelf life causes injury to S. aureus.
• To quantify the conditions under which S. aureus injury occurs.

Main Methods:

• Raw milk was inoculated with S. aureus FRIA-100 (approx. 10^6 cells/ml).
• Minas cheese was stored for 40 days and Mozzarella for 60 days at 7°C.
• Acidity, pH, and S. aureus counts (traditional and repair methods) were assessed every 2-3 days.

Main Results:

• S. aureus growth was monitored throughout the shelf life of both cheese types.
• Bacterial injury was observed at acidity levels ranging from 0.7% to 0.8% lactic acid.
• A higher bacterial count (1.3 log) was indicative of injured S. aureus cells.

Conclusions:

• Increasing acidity in fresh cheeses can lead to S. aureus injury.
• Specific acidity thresholds (0.7-0.8% lactic acid) are associated with S. aureus injury.
• The findings highlight the importance of monitoring acidity for controlling S. aureus in cheese production.