Abstract
Conditions influencing Bacillus cereus growth and cereulide production, such as temperature and pH, were evaluated at varying incubation periods. The growth and cereulide production at different temperatures and pH values ranging from 10 to 40 ºC and 5.0 to 8.5, respectively showed that the temperature from 20 to 30 ºC and at pH from 6.0 to 7.0 gave the optimum growth and cereulide production by B. cereus SA105. pH below 6.0 resulted in reduced growth and cereulide production. Cereulide production increased along with the incubation period, and maximum cereulide titre (ng/mL) of 1219.1±8.90 was obtained after 6 days of incubation at 30 ºC and pH 6.5 under static conditions. There was no quantifiable toxin at incubation temperatures of 10 and 40 ºC by B. cereus SA105. This work further reveals that B. cereus growth and cereulide production was significantly affected by temperature and pH in relation to the incubation period. Furthermore, the findings of this study will serve as a means for reducing the diversity of emetic toxin-producing B. cereus population in food and food products, thus preventing food poisoning.
Highlights
Bacillus cereus, a Gram-positive, rod-shaped, beta haemolytic, endemic soil-dwelling bacterium is a common cause of food poisoning around the world (Turnbull, 1996)
The optimum temperature (30 oC) for B. cereus SA105 recorded is in accordance with the report of previous authors who observed the optimum temperature for the growth of B. cereus to be between 30-37 oC (European Food Safety Agency, 2005; Nguyen-The, Carlin, & Guinebretiere, 2003)
Evaluation of the effect of pH on the growth rate of the emetic strain of B. cereus in this study revealed that it grew best from pH 6.0 to 7.0 and that it is not acid-tolerant
Summary
A Gram-positive, rod-shaped, beta haemolytic, endemic soil-dwelling bacterium is a common cause of food poisoning around the world (Turnbull, 1996). The emetic syndrome was first identified in the 1970s and was associated with the consumption of fried rice (Kramer & Gilbert, 1989) This syndrome is an intoxication caused by B. cereus emetic toxin, called cereulide which is secreted in foods before ingestion. Yokoyama et al (1999) suggested that more than 90% of food poisoning caused by B. cereus is of the emetic type in countries of the Far East. This may be partly due to the wide consumption of rice, which is a well-known food vehicle for the emetic toxin. We compare and assess the effects of temperature and pH on growth and cereulide production of B. cereus at different days of incubation
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