Injury to Staphylococcus aureus during sausage fermentation.

Area of Science:

• Food Microbiology
• Bacterial Physiology
• Food Safety

Background:

• Staphylococcus aureus is a significant pathogen in food products.
• Fermentation processes in sausages can impact bacterial viability.
• Understanding bacterial injury is crucial for accurate microbial assessments.

Purpose of the Study:

• To investigate the effect of fermentation on Staphylococcus aureus viability in beef sausages.
• To determine if lactic acid produced during fermentation causes bacterial injury.
• To assess the recovery of injured Staphylococcus aureus.

Main Methods:

• Inoculation of beef sausage with Staphylococcus aureus 196E.
• Fermentation at 35°C with varying glucose concentrations and starter cultures.
• Plating on tryptic soy agar (TSA) and TSA with 7.5% NaCl.
• Incubation at 5°C followed by reincubation at 35°C.

Main Results:

• Staphylococcus aureus showed reduced growth on selective media (TSA with 7.5% NaCl) due to fermentation-induced injury.
• Lower glucose concentrations (higher acidity) exacerbated the injury.
• Injured bacteria recovered viability upon reincubation at 35°C after cold storage.
• No injury was observed in the absence of glucose or starter culture.

Conclusions:

• Lactic acid produced during sausage fermentation causes reversible injury to Staphylococcus aureus.
• Bacterial injury must be considered for accurate enumeration of viable Staphylococcus aureus in fermented sausages.
• Fermentation conditions significantly influence the viability and injury status of Staphylococcus aureus.