Bacillus cereus in Samples of Pre-cooked and Cooked Rice for Sale to the Public in Colima State, Mexico

Abstract

Bacillus cereus is recognized as a pathogen that causes food poisoning. There have been outbreaks associated with the consumption of rice contaminated with this bacterium. It is one of the few pathogens with the ability to spoil food. Outbreaks of diarrheal and emetic syndromes caused by this organism have been widely reported in Mexico, Japan, the United States, the Netherlands, Thailand, Africa, South Korea, the United Kingdom, Belgium, and Finland. In Mexico, there are no data available to evaluate the epidemiological importance of B. cereus as a causative agent of enteric diseases, although its possible presence in parboiled and cooked rice could represent a health risk. Thus, the objective of this work was to identify the presence of B. cereus in parboiled and cooked rice for sale to the public in Colima, Mexico. The health quality, the quantity of B. cereus present and the identification of strains of the hblA and ces genes, which are involved in diarrheal and emetic syndrome, respectively, were determined. 155 samples of cooked and 32 precooked rice were collected from different establishments in the city of Colima (homes, fixed and street restaurants, inns and supermarkets). Sanitary quality was evaluated by observing the counts of aerobic mesophilic bacteria and total coliform bacteria, which were carried out following the current official methodology. The B. cereus count was performed on MYP agar (mannitol, yolk egg and polymyxin). Finally, the identification of diarrheal or emetic B. cereus strains was by amplification of the hblA and ces genes by PCR. In 87.5 % of the parboiled rice samples and in 23.2 % of the cooked rice samples, high counts of aerobic mesophilic bacteria were obtained (> 10⁵ CFU / g), and in 71 % of the total samples analyzed it was demonstrated the presence of viable total coliform bacteria. In 28.1 % of the parboiled rice samples and in 89 % of the cooked rice samples, B. cereus was recovered. The hblA gene (encoding one of the three BL hemolysin subunits) was amplified in 86 % of B. cereus isolates, however, no strains carrying the ces gene (encoding cereulide) were identified. All samples of the cooked or parboiled rice samples containing vegetables (corn, potato, green bean, carrot and pea) showed the presence of B. cereus, so these ingredients may be related to the presence of the pathogen in cooked rice or precooked. Even in figures far below those considered as a health risk, if it is stored under conditions of temperature abuse, as is often the case in the sampled sites, contaminated rice can represent a risk to the health of the consumer.