Development and application of a centrifugation-plating method to study the biodiversity of Bacillus species in rice products (original) (raw)
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Risk of Bacillus cereus in Relation to Rice and Derivatives
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Rice is a very popular food throughout the world and the basis of the diet of the citizens of many countries. It is used as a raw material for the preparation of many complex dishes in which different ingredients are involved. Rice, as a consequence of their cultivation, harvesting, and handling, is often contaminated with spores of Bacillus cereus, a ubiquitous microorganism found mainly in the soil. B. cereus can multiply under temperature conditions as low as 4 °C in foods that contain rice and have been cooked or subjected to treatments that do not produce commercial sterility. B. cereus produces diarrhoeal or emetic foodborne toxin when the consumer eats food in which a sufficient number of cells have grown. These circumstances mean that every year many outbreaks of intoxication or intestinal problems related to this microorganism are reported. This work is a review from the perspective of risk assessment of the risk posed by B. cereus to the health of consumers and of some con...
Detection of toxigenic Bacillus cereus and Bacillus thuringiensis spores in U.S. rice
International Journal of Food Microbiology, 2009
Bacillus cereus is a gram-positive, endospore forming pathogenic bacterium that is ubiquitous in the environment and is frequently associated with emetic and diarrheal types of foodborne illness. In this study, 178 samples of raw rice from retail food stores were analyzed for the presence of B. cereus spores. Spores of Bacillus species were found in 94 (52.8%) of the rice samples with an average concentration of 32.6 CFU/g (3.6-460 CFU/g for B. cereus and 3.6-23 CFU/g for Bacillus thuringiensis). Eighty three of the 94 isolates were identified as B. cereus and 11 were identified as B. thuringiensis. Bacillus mycoides (240 CFU/g) was the predominant isolate in one rice sample. Using PCR the isolates were checked for the presence of the cereulide synthetase gene (ces), the hblA and hblD genes of the hemolysin BL (HBL) complex and the nheA and nheB genes of the nonhemolytic (NHE) enterotoxin complex. The ces gene was not identified in any of the isolates. By contrast 47 (56.6%) B. cereus isolates possessed the hblA and hblD genes and 74 (89.1%) isolates possessed the nheA and nheB genes. As determined by commercial assay kits, forty four (53.0%) of the 83 B. cereus isolates produced both NHE and HBL enterotoxins whereas 78 (93.9%) were positive for either one or the other. Protein toxin crystals were detected visually in the 11 B. thuringiensis isolates. PCR analysis revealed 10 (90.9%) of those 11 isolates carried the cry gene. All the B. thuringiensis isolates were positive for NHE and HBL enterotoxins. Our results suggest that foodborne illness in the U.S. due to B. cereus with rice as the vehicle would be most likely associated with the diarrheal-type syndrome.
Bacillus cereus and Bacillus thuringiensis in ready-to-eat cooked rice in Malaysia
Bacillus cereus (B. cereus) isolates are toxigenic and can cause food poisoning. Cooked rice is a potentially hazardous food, especially in tropical countries. The aim of this study was to determine the prevalence of B. cereus and B. thuringiensis in raw and cooked rice marketed in Selangor, Malaysia. A combination of Most Probable Number-Polymerase Chain Reaction (MPN-PCR) method was used to detect gyrB gene in B. cereus and B. thuringiensis. Five local varieties of raw rice samples were negative for B. thuringiensis but all (100%) were positive for B. cereus. A total of 115 cooked rice samples (nasi lemak, nasi briyani, nasi ayam and nasi putih) were studied for the presence of B. cereus and B. thuringiensis. Nasi ayam was found to have the highest prevalence (100%) of B. cereus compared to nasi putih (76.2%) and nasi lemak (70.4%). Nasi briyani had the lowest prevalence (50%) of B. cereus. The frequencies of B. thuringiensis were found to be 10, 30 and 35.2 % in nasi putih and nasi ayam, nasi briyani and nasi lemak, respectively. Occurrence of B. cereus and B. thuringiensis in the samples ranged from < 3 to 1100 MPN/g in different samples. Maximum number of B. cereus was observed in nasi lemak, nasi briyani and nasi putih (> 1100 MPN/g) while nasi ayam showed less contamination (460 MPN/g) with B. cereus which was significantly different (P < 0.05) from others. The number of B. thuringiensis in nasi lemak, nasi briyani, nasi putih and nasi ayam were found to be >1100, 93, 9.2 and 3.6 MPN/g, respectively.
1999
As 16S rRNA sequence analysis has proven inadequate for the differentiation of Bacillus cereus from closely related species, we employed the gyrase B gene (gyrB) as a molecular diagnostic marker. The gyrB genes of B. cereus JCM 2152(T), Bacillus thuringiensis IAM 12077(T), Bacillus mycoides ATCC 6462(T), and Bacillus anthracis Pasteur #2H were cloned and sequenced. Oligonucleotide PCR primer sets were designed from within gyrB sequences of the respective bacteria for the specific amplification and differentiation of B. cereus, B. thuringiensis, and B. anthracis. The results from the amplification of gyrB sequences correlated well with results obtained with the 16S rDNA-based hybridization study but not with the results of their phenotypic characterization. Some of the reference strains of both B. cereus (three serovars) and B. thuringiensis (two serovars) were not positive in PCR amplification assays with gyrB primers. However, complete sequencing of 1.2-kb gyrB fragments of these reference strains showed that these serovars had, in fact, lower homology than their originally designated species. We developed and tested a procedure for the specific detection of the target organism in boiled rice that entailed 15 h of preenrichment followed by PCR amplification of the B. cereus-specific fragment. This method enabled us to detect an initial inoculum of 0.24 CFU of B. cereus cells per g of boiled rice food homogenate without extracting DNA. However, a simple two-step filtration step is required to remove PCR inhibitory substances.
Prevalence and characterisation of Bacillus cereus in cooked rice retailed in Ilara-mokin, Nigeria
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Bacillus cereus is widely distributed in different food products and causes a variety of symptoms associated with food poisoning. Rice has been suggested as a vehicle for contamination and being involved in B. cereus intoxication. Based on the aforementioned risks, studies of Bacillus cereus incidence along with its isolation and characterization are essential to establishing the safety of cooked rice. Using the selective culture technique, pure isolates of Bacillus cereus strains were characterized and identified based on cultural, and biochemical features. Characterization was done on the ability of the bacterial strains to hydrolyse casein and starch, ferment lactose, and lyse red blood cells (haemolysis). Out of the 47 samples screened, 45 isolates were detected in 14 samples. Antibiotic susceptibility testing revealed that all isolates showed resistance to Ampicillin (10 μg), but were susceptible to Erythromycin (15 μg), Vancomycin (30 μg), Tetracycline (30 μg), Ampicillin (10 ...
Inactivation of Bacillus cereus Spores during Rice Cooking
Food Science and Technology Research, 2004
The D-values at 80, 90 and 100'C of Bacillus cereus spores (Philippine strain 1061) in 2% broth of Philippine rice cultivar PSB Rc72H were 38, 12 and 5 min, respectively. The Z-value of the test spore was 20'C. The mathematically calculated lethality for the Bacillus spores in rice cooked at 100'C was established to be 25 min, which could be adequately attained during normal rice cooking times of ~25 min by boiling.
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Dry heat inactivation of Bacillus cereus in rice
Czech Journal of Food Sciences, 2008
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Enumeration, isolation and characterization of Bacillus cereus strains from Spanish raw rice
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