"FROM PLATE TO PATHOGEN: THE IMPACT OF BACILLUS CEREUS IN STORED RICE"
Rice is the staple main course in many parts of the world, not just because of its nutritious content but also due to cultural significance, especially in countries of Asia. Bacillus cereus which is a gram positive, rod-shaped, aerobic and facultative anaerobic, ubiquitous bacteria. They also produce toxins and cause foodborne illness; diarrheal and emetic syndrome, when the contaminated food is consumed, because of their ability to produce endospores in unfavorable conditions they are resistant to environmental stresses.
When Bacillus cereus enters the stomach due its resistant nature, it survives in the acidic environment and invades the intestinal lining. They compete with the gut microbiota for nutrients and space and eventually build up biofilm using quorum sensing. The biofilm helps the bacteria to stick to the surface of the lining and becomes resilient to the environmental stresses like immunity, and antibiotics.
The diarrheal syndrome arises from the small intestine, when the three key toxins associated with food poisoning have been identified as hemolysin BL (Hbl), non-hemolytic enterotoxin (Nhe), and cytotoxin K (CytK). Cereulide, the heat- and acid- resistant toxin which stabilises and resists proteolytic degradation, is responsible for the emetic syndrome that typically causes vomiting after consuming the food. It is synthesized by non-ribosomal peptide synthetases that cause cell damage in animal cells and inhibit human immune cells. Due to increased use of Refrigerated Processed Foods of Extended Durability (REFPEDs), and immunocompromised population, the foodborne illness is expected to rise.
The experiment began with preparing four different samples of the freshly boiled rice; a) rice stored in room temperature for 24 hours b) stored in refrigerator for 24 hours c) stored in refrigerator for 72 hours d) stored in refrigerator for 120 hours. To prepare the rice extract 3mL of sterile saline solution was mixed with the rice and grinded in aseptic conditions. The rice extract was streaked on the different medium agars like nutrient agar, Bacillus cereus agar, blood agar, etc. After incubation for 24 hours the isolated colonies were isolated and examined. B.cereus is beta hemolytic.
On performing preliminary identification tests, B.cereus was found to be catalase positive and motile due to the presence of the flagella. It was further characterized by performing biochemical tests,it was found to be methyl red (a fermentative path tracing test) positive, an alkaline slant and an alkaline butt in triple sugar iron test, and positive for citrate utilization test and urease.
The results indicated that the microbial colonies in the rice stored in the room temperature have more growth than the refrigerated rice sample. But in refrigerated samples as the time span increases the microbial load also increases.
To prevent food poisoning caused by B.cereus it is important to follow prompt refrigeration and reheating. It is necessary to consume the food item fresh if not possible at the moment, avoid storing in the room temperature and practice safe food storage.
IMAGE REFERENCE
REFERENCE
Mahbubani S, Vani GS. ISOLATION & IDENTIFICATION OF Bacillus cereus FROM COOKED RICE AT REFRIGERATED & UNREFRIGERATED CONDITIONS.
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