Inactivation of Bacillus cereus Spores during Rice Cooking (original) (raw)
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Food Control, 2016
Bacillus cereus is a pathogenic spore-forming bacterium implicated in cases of diarrheal and emetic type of foodborne illness. We previously found that enterotoxigenic B. cereus is widely present in retail spices. Here we analyzed the spore heat resistance of nine diarrheal strains isolated from spices. Seven had D 95°C values ranging from 0.64-3.53 min while two emetic strains had D 95°C values of 7.04 min and 6.64 min. The ability of selected strains to grow in cooked rice at temperatures 20°C, 17°C and 12°C was determined as well as their toxin expression capability. After 48 h, B. cereus levels of 1.26 X 10 7 and 3.8 x 10 7 CFU/ g were obtained in cooked rice maintained at 17°C and 20 °C respectively. At 12 °C, counts did not reach 10 4 CFU/g even after 48 h of incubation. The increase in the aerobic, mesophilic bacterial population (APC) and B. cereus population naturally present in 0.1% crushed pepper added to cooked rice was determined over a period of 48 h at 20°C and 17°C. Levels of B. cereus in pepper/rice samples reached a maximum of 1600 MPN/g at 20 °C while the APC was 2.4 x 10 8 /g at this temperature. When thyme, containing the same initial natural level of B. cereus, was added to rice in place of pepper, more than a five-fold greater level of B. cereus was detected at 20°C. Since thyme contained initial APC of 2.5 log 10 less than pepper we conclude that the high APC functions in a competitive-exclusion manner, minimizing the growth of B. cereus and potentially other agents of foodborne illness. This is particularly relevant in instances of temperature abuse of foods and may explain the low incidence of foodborne illness due to B. cereus despite its widespread presence shown in previous surveys of market spices.
Dry heat inactivation of Bacillus cereus in rice
Czech Journal of Food Sciences, 2008
The aim of this work was to validate the method of decontamination of rice at the temperature of 120°C (determined as optimal in previous experiments). Bacillus cereus was selected as the marker micro-organism for the monitoring of decontamination. The spores of Bacillus cereus are moderately heat resistant. In order to show the efficacy of our decontamination process, we artificially contaminated the rice under study with B. cereus. Decontamination was carried out in a homogenising steriliser about 20 h after contamination. The sample was first heated to 90°C and held at this temperature for 70 minutes. Then the temperature was increased to 120°C and held for 3 hours. Five samples were taken for microbiological analyses as follows: before the experiment, on reaching 120°C, and then after 1, 2, and 3 h of decontamination. Decontamination of rice from vegetative forms and spores of B. cereus present at the level of 400 CFU/ml was effected by heating to 120°C and holding for 1 hour.
Risk of Bacillus cereus in Relation to Rice and Derivatives
Foods, 2021
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...
Prevalence and characterisation of Bacillus cereus in cooked rice retailed in Ilara-mokin, Nigeria
Journal of Food Safety and Hygiene
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 ...
Food Control, 2009
The effect of storage temperature abuse on the growth and physiology of Bacillus cereus in cooked rice was examined using plate counting and flow cytometry (FCM). Concurrently, toxigenic potential was measured through recording phosphatidylcholine-specific phospholipase C (PC-PLC) activity. Rice spiked with endospores was incubated at 4°C, 10°C or 18°C for 6 days. Growth was not recorded at 4°C, whereas >1.0 Â 10 6 CFU g À1 were detected at 10°C and 18°C. PC-PLC activity was temperature dependent and was not destroyed by microwaving. FCM population profiling complemented plate count data, providing novel physiological data e.g. on the membrane integrity, redox or intracellular activities of cells over time during low temperature incubation.
Enumeration, isolation and characterization of Bacillus cereus strains from Spanish raw rice
Food Microbiology, 2002
Bacillus cereus was present in 61 samples of raw rice analysed representing unhusked, husked and commercial origins. B. cereus in husked and white rice samples did not reach 10 2 cfu g À1 , while in the unhusked rice B. cereus densities exceeded 10 3 cfu g À1 . Processing steps such as drying, husking and polishing reduced the number of B. cereus in the ¢nal product. Eight strains with typical morphology of B. cereus on Polymyxin^Mannitol^EggYolk^Phenol Red Agar (PMYPA) were isolated. According to ISO con¢rmatory tests, the API System tests and supplementary tests of motility, oxidase activity and enterotoxin production, these isolates were characterized and identi¢ed as B. cereus. All strains were motile, oxidase-negative and produced diarrheal enterotoxin inTSB. D and z-values were used to characterize heat resistance of spores obtained from the eight strains of B. cereus characterized. A large diversity in heat resistance was observed among the isolates. At 901C, D-values ranged from 2?23 to 23?26 min, with ¢ve groups of D-value means signi¢cantly di¡erent at the 95% con¢dence level. D 95and D 100 values calculated for the eight strains ranged from 0?69 to 5?17 min and from 0?43 to 1?09 min, respectively. Statistical analysis revealed that there was signi¢cant di¡erence between the D-value means obtained for the strains at each temperature.The z-values for the eight strains of B. cereus tested in this study ranged from 7?421C to 8?201C with an average of 7?71C.
International Journal of PharmTech Research, 2015
The aim of this study has been an investigation of the presence of Bacillus cereus and detection of enterotoxigenic genes in cooked rice samples through utilizing a PCR technique. In this study the providence of B.cereus was carried out to cooked rice samples and the B.cereus isolates were investigated for enterotoxigenic gene. The cooked rice samples were purchased from several restaurants in the area of (Bangi, Kajang and UKM) Selangor, Malaysia. A total of 70 samples have been analyzed. B. cereus contamination has been formed between 1.2 × 10 4 to 1.6 × 10 6 cfu/g cooked of 110 colonies of tentative B. cereus have been tested onto mannitol egg yolk polymyxin agar and Chromogenic Bacillus cereus Agar, and 35 colonies have been detected as B. cereus using biochemical test and partial sequence of 16s r DNA sequences analysis. The B. cereus isolates that are BC1 to BC35 have been distinguished for hemolytic enterotoxin (HBL complex encoding gene (hblD), and ematic (ces) gene toxin. 12 isolates have been reported to be positive towards hblD, None of the B. cereus isolates have been found positive towards ematic(ces) gene. Therefore, the presence of B. cereus and their enterotoxigenic genes in cooked rice samples can be regarded as a potential risk for public health.
Predictive model for growth of Bacillus cereus during cooling of cooked rice
International journal of food microbiology, 2018
Bacillus cereus is frequently implicated in foodborne outbreaks associated with the consumption of cooked rice. The main contributing factors leading to outbreaks is rice cooked in large quantities and subsequently, inadequately chilled or stored at room temperatures for a prolonged period of time prior to consumption. Bacillus cereus growth in cooked rice inoculated with approximately 2 log CFU/g of heat-shocked (80 °C/10 min) spores at several isothermal conditions (between 10 and 49 °C) was quantified. B. cereus populations were determined by plating on mannitol egg yolk polymyxin agar and incubating at 30 °C for 24 h. Primary growth models, namely Baranyi, Huang, modified Gompertz, and logistic models were fitted to growth data. Specific growth rates from all four primary models were used to fit the modified Ratkowsky square-root model with respect to temperature. All four primary models were well fitted by the modified Ratkowsky model (R values from 0.90-0.99). Based on the goo...
Behavior of an Emetic Bacillus cereus Strain in Rice Food
2018
Subject description: This article deals with the possible competitiveness of emetic B. cereus against nonemetics, likely to confer a development advantage to the first mentioned. The goal of this study was to evaluate the behavior of an emetic strain with respect to other B. cereus contaminants. Method: A rifampicin-resistant mutant of the emetic strain k5975c was grown in Luria-Bertani. Broth overnight at 30°C, then inoculated in cooked rice or in naturally contaminated rice and incubated for 24 h at 23°C and 30°C. The emetic toxin and its toxicity were detected using the boar sperm motility inhibition bioassay and the liquid chromatography-ion trap mass spectrometry (LC-MS). Results: With an inoculum level of ca. 6 log CFU g-1, the emetic strain showed unhampered growth in rice contaminated by other B. cereus at both incubation temperatures, although it did not inhibit the growth of B. cereus contaminants. When the inoculum level of the emetic strain was reduced to ca. 3 log CFU g...