A probability model for enterotoxin production of Bacillus cereus as a function of pH and temperature

Effects of Lactic Acid and Salt on Enterotoxin A Production and Growth of Staphylococcus aureus

Food poisoning caused by Staphylococcus aureus is responsible for staphylococcal enterotoxin (SE) produced in foods. Staphylococcal food poisoning is mostly caused by staphylococcal enterotoxin type A (SEA) among SEs. Growth/no growth for S. aureus under various environmental conditions was well studied with a logistic regression model so far. Recently we successfully described the boundaries of SEA production and growth of S. aureus in broth at various temperatures and salt concentrations with the model. In this study, the effects of lactic acid and salt on SEA production and growth of S. aureus was quantitatively studied. Consequently the boundaries of SEA production and growth of S. aureus cocktail in broth at various combinations of salt concentrations and pH values that were adjusted with lactic acid were successfully described with a logistic regression model. Here the cocktail was incubated in stationary culture at 30 °C and 10 °C. The maximum toxin production and cell growth of the cocktail were observed both at 5% salt in the pH range from 4.5 to 7.0. Also, the characteristics of individual strains of the cocktail in SEA production and growth at 30 °C and 10 °C were found to be specific to the strains. The present study revealed the effect of lactic acid and salt on SEA production and growth of S. aureus as well as the variety of SEA production and growth of S. aureus strains. These results would become useful information in food industry to prevent staphylococcal food poisoning. PRACTICAL APPLICATION: Boundaries of enterotoxin A production/no production and growth/no growth of staphylococcal cocktail at various combinations of pHs adjusted with lactic acid and salt concentrations were well described with a logistic regression model. The maximum toxin production and cell growth were observed both at 5% salt in the pH range from 4.5 to 7.0. A variety of the toxin production and cell growth were observed in terms of pH and salt concentration among individual strains of the cocktail.

Comprehensive Study of the Boundaries of Enterotoxin A Production and Growth of Staphylococcus aureus at Various Temperatures and Salt Concentrations

Staphylococcus aureus food poisoning, which is still a serious health problem worldwide, is caused by the intoxication of staphylococcal enterotoxin (SE). Among many types of SE, staphylococcal enterotoxin type A (SEA) is known to be the most responsible for S. aureus food poisoning worldwide. Several researchers have reported the modeling of growth/no growth boundaries for S. aureus with a logistic regression model. In this study, the boundaries of SEA production and S. aureus growth in broth were first performed with the logistic regression model, to evaluate the effects of environmental factors of temperature and salt. Consequently, the boundaries of SEA production and growth of S. aureus in temperature and salt concentration could be produced with the model in shaking and stationary cultures. The area where S. aureus cells would grow, but not produce SEA could be shown between the boundaries of SEA production and growth. Internal and external validations showed that the model could well describe and predict experimental results. Further, the maximum concentrations of SEA and cell population under various conditions of temperature and salt concentration were also compared between the shaking and stationary cultures. These results obtained in this study would become useful information in food industry to prevent S. aureus food poisoning outbreaks. PRACTICAL APPLICATION: Production/no production of staphylococcal enterotoxin A at various temperatures and salt concentrations in shaking and stationary cultures could be estimated well with a logistic regression model. Growth/no growth of staphylococcal cells under the same conditions was also well estimated with the model. The area where S. aureus cells would grow, but not produce SEA could be shown with the model. This present analysis would provide useful information in food industry to prevent staphylococcal food poisoning outbreaks.

Modeling the Effect of Water Activity, pH, and Temperature on the Probability of Enterotoxin A Production by Staphylococcus aureus

The objectives of this study were to develop a probability model of Staphylococcus aureus enterotoxin A (SEA) production as affected by water activity (a(w)), pH, and temperature in broth and assess its applicability for milk. The probability of SEA production was assessed in tryptic soy broth using 24 combinations of a(w) (0.86 to 0.99), pH (5.0 to 7.0), and storage temperature (10 to 30°C). The observed probabilities were fitted with a logistic regression to develop a probability model. The model had a concordant value of 97.5% and concordant index of 0.98, indicating that the model satisfactorily describes the probability of SEA production. The model showed that a(w), pH, and temperature were significant factors affecting the probability of toxin production. The model predictions were in good agreement with the observed values obtained from milk. The model may help manufacturers in selecting product pH and a(w) and storage temperatures to prevent SEA production.

Total phenolic and flavonoid content and antibacterial activity of Punica granatum L. var. pleniflora flowers (Golnar) against bacterial strains causing foodborne diseases

BACKGROUND

Flowers of Punica granatum L. (Punicaceae) var. pleniflora, known as "Golnar" in Iranian traditional medicine have been used for the prevention and treatment of foodborne diseases. In this study, antibacterial activities of ethanol extract of Golnar and its fractions were scientifically evaluated against bacteria causing foodborne diseases including Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes, Escherichia coli, Shigella dysantriae, and Salmonella typhi. The total phenolic and flavonoid contents of the extract and its fractions were also determined.

METHODS

The antibacterial effect of the ethanol extract and its fractions were primarily evaluated by agar well diffusion and their MIC and MBC were determined by broth macro dilution method. The total phenolic and flavonoid contents of the extract and its fractions were measured based on gallic acid and rutin equivalents (GAE and RE), respectively.

RESULTS

After evaluation of total phenolic and flavonoid content the chloroform fraction showed the lowest phenolic and flavonoid contents (3.8 mg GAE/g and 1.1 mg RE/g respectively) and the methanol fraction showed the highest phenolic and flavonoid contents (18.1 mg GEA/g and 3.3 mg RE/g respectively). The total phenolic and flavonoid content was positively associated with the antibacterial activities of the fractions with chloroform extract exhibiting lowest antibacterial activity against E. coli (MIC 25 mg/ml) and the methanol fraction exhibiting the highest antibacterial effect against S. aureus (MIC 0.19 mg/ml).

CONCLUSION

Golnar extract showed antibacterial activity against both Gram positive and Gram negative bacteria causing food poisoning. Therefore, the extract can be used for prevention or treatment of foodborne diseases or as preservative in the food industry. The methanol fraction with the highest phenolic and flavonoid content showed the highest antibacterial effect. This indicates that the phenolic and flavonoid compounds in the extract can be responsible for the effect.