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Growth and Enterotoxin Production of Staphylococcus aureus in Fresh Packaged Mushrooms ( Agaricus bisporus )
Stefan T Martin1, Robert B Beelman1
1Department of Food Science, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Abstract:
Freshly harvested mushrooms were found to induce a near-anaerobic environment (<2% O2) in unventilated, PVC-overwrapped packages within 2 to 6 h when incubated at 20 to 30°C. Mushrooms were inoculated with an enterotoxigenic strain of Staphylococcus aureus and incubated in overwrapped trays at different temperatures. S. aureus grew and produced staphylococcal enterotoxin (SE) in unventilated PVC-overwrapped mushroom packages when inoculated at levels of 103, 104, and 105 CFU/g of mushroom after 4 days of incubation at 30°C. Growth of S. aureus was observed at all levels of inoculation at 25°C, but no SE was detected after 7 days of incubation. When mushroom packages were ventilated, S. aureus growth was suppressed and no SE was detected after 7 days at 25°C and 4 days at 30°C. However, S. aureus growth in ventilated packs exceeded growth in unventilated packages when the incubation temperature was increased to 35°C; SE was detected within 18 h of incubation at this temperature, even in mushrooms inoculated at a low level (102 CFU/g). These results show the extreme importance of proper sanitation and worker hygiene during mushroom harvesting and packaging, ventilation of fresh mushroom packages, and proper storage temperatures for fresh mushrooms at all points of the food chain.
Insights
Fresh mushrooms in sealed packages quickly create low-oxygen conditions. This environment promotes Staphylococcus aureus growth and toxin production, especially at warmer temperatures, highlighting the need for proper handling and ventilation.
Area of Science:
- Food Microbiology
- Food Safety
- Horticultural Science
Background:
- Fresh mushrooms are susceptible to microbial contamination during post-harvest handling.
- Packaging conditions can significantly influence microbial growth and toxin formation in fresh produce.
Purpose of the Study:
- To investigate the impact of packaging environment and temperature on Staphylococcus aureus growth and staphylococcal enterotoxin (SE) production in fresh mushrooms.
- To determine the role of ventilation in mitigating microbial risk in packaged mushrooms.
Main Methods:
- Fresh mushrooms were packaged in PVC overwraps and incubated under varying temperatures (20-35°C) with and without ventilation.
- Inoculation with Staphylococcus aureus at different concentrations (10^2 to 10^5 CFU/g).
- Monitoring of oxygen levels, bacterial growth, and staphylococcal enterotoxin (SE) production.
Main Results:
- Unventilated packages rapidly developed near-anaerobic conditions (<2% O2) within 2-6 hours at 20-30°C.
- Staphylococcus aureus grew and produced SE in unventilated packages at 30°C within 4 days.
- Ventilation suppressed S. aureus growth and SE production at 25°C and 30°C, but higher temperatures (35°C) with ventilation led to rapid toxin production.
Conclusions:
- Proper ventilation and temperature control are critical for preventing Staphylococcus aureus growth and staphylococcal enterotoxin (SE) production in fresh mushrooms.
- Emphasizes the importance of sanitation, worker hygiene, and temperature management throughout the mushroom supply chain to ensure food safety.
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