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Effect of sodium chloride and pH on enterotoxin C production
Insights
High salt concentrations inhibit Staphylococcus aureus growth and enterotoxin C production. Even at optimal pH, 12% NaCl prevented toxin formation, similar to enterotoxin B patterns.
Area of Science:
- Food Microbiology
- Bacterial Toxinology
- Food Safety
Background:
- Staphylococcus aureus is a significant foodborne pathogen.
- Enterotoxins produced by S. aureus can cause food poisoning.
- Environmental factors like salt concentration and pH influence bacterial growth and toxin production.
Purpose of the Study:
- To investigate the impact of varying sodium chloride (NaCl) concentrations and initial pH on the growth of Staphylococcus aureus.
- To determine the conditions supporting the production of enterotoxin C by S. aureus.
- To compare the effects of NaCl on enterotoxin C production with those on enterotoxin B.
Main Methods:
- Staphylococcus aureus strain 137 was cultured in N-Z Amine NAK broths with 0-12% NaCl.
- Initial pH ranged from 4.00 to 9.83.
- Incubation was performed at 37°C for 8 days, monitoring growth and enterotoxin C production.
Main Results:
- Bacterial growth occurred across a wide pH range (4.00-9.83) at 0% NaCl with sufficient inoculum.
- Growth rate decreased significantly with increasing NaCl concentrations up to 12%.
- Enterotoxin C production was observed between pH 4.00-9.83 at 0% NaCl, pH 4.40-9.43 at 4% NaCl, and pH 4.50-8.55 at 8% NaCl.
- At 10% NaCl, enterotoxin C production was limited to pH 5.45-7.30 (high inoculum) or pH 6.38-7.30 (lower inoculum).
- No enterotoxin C was detected at 12% NaCl, regardless of pH.
- NaCl's inhibitory effect on enterotoxin C production mirrored its effect on enterotoxin B.
Conclusions:
- NaCl concentration is a critical factor limiting Staphylococcus aureus enterotoxin C production.
- High salt levels (≥10%) significantly restrict the pH range for enterotoxin C synthesis.
- 12% NaCl completely inhibited enterotoxin C production under the tested conditions.
Abstract:
Growth and production of enterotoxin C by Staphylococcus aureus strain 137 in 3% + 3% protein hydrolysate powder N-Z Amine NAK broths with 0 to 12% NaCl and an initial pH of 4.00 to 9.83 were studied during an 8-day incubation period at 37 C. Growth was initiated at pH values as low as 4.00 and as high as 9.83 at 0% salt level as long as the inoculum contained at least 10(8) cells per ml. Rate of growth decreased as the NaCl concentration was increased gradually to 12%. Enterotoxin C was produced in broths inoculated with 10(8) cells per ml and above and having initial pH ranges of 4.00 to 9.83, 4.40 to 9.43, 4.50 to 8.55 and respective NaCl concentrations of 0, 4, and 8%. In the presence of 10% NaCl, the pH range supporting enterotoxin C production was 5.45 to 7.30 for an inoculum level of 10(8) cells per ml and 6.38 to 7.30 for 3.6 x 10(6) cells per ml. In repeated experiments in which the inoculum contained 10(8) cells per ml, we failed to demonstrate enterotoxin C production in broths with 12% NaCl and a pH range of 4.50 to 8.55 and concentrated up to 14 times. The effect of NaCl on enterotoxin C production followed the same pattern as its effect on enterotoxin B production. As the concentration of NaCl increased from 0 to 10%, yields of enterotoxin B and C decreased to undetectable amounts.