Food poisoning from rice and pasta

Foodborne illnesses, including food poisoning, are major public health concerns. These illnesses impose significant annual costs on various countries, regardless of their development status. Bacillus cereus is a known pathogen that causes food poisoning. Due to its ability to produce resistant spores (a resistant form of bacteria), it can easily survive in various environments, including raw and processed foods, leading to illness. However, the exact prevalence of diseases caused by this bacterium remains unclear, as they are often non-fatal, mild, and go undiagnosed.

Growth Conditions, Habitat, and Resistance Characteristics of Bacillus cereus

Bacillus cereus is a Gram-positive, rod-shaped bacterium capable of forming spores, its resistant form. This ability allows it to survive harsh environmental conditions like extreme temperatures, varying pH levels, and other unfavorable conditions. Different Bacillus cereus species can grow in a wide temperature range, from approximately 5 to 55 degrees Celsius. This adaptability enables the bacterium to thrive in diverse environments with varying temperatures. However, the optimal growth temperature for these bacteria is around 30 to 37 degrees Celsius, providing ideal conditions for their multiplication and activity.

The bacterium can grow within a pH range of 5 to 9 but prefers neutral to slightly alkaline conditions (pH 6 to 7). It can also grow under both aerobic and anaerobic conditions, demonstrating its adaptability to various environments. Additionally, Bacillus cereus can form biofilms, which increase its resistance to harsh conditions and make it difficult to eradicate from the environment.

Bacillus cereus is naturally found in various environments like soil, water, plants, and dust, and is commonly present in food products of plant and animal origin. It can easily transfer to human environments, particularly kitchen equipment and food processing areas, which become potential sources of food contamination.

Foods Susceptible to Bacillus cereus Contamination

Bacillus cereus is a resistant bacterium that grows in many food items. Some foods, due to their specific characteristics, provide a suitable environment for Bacillus cereus growth, increasing the likelihood of contamination.

1. Starchy Foods

Starchy foods like cooked rice, pasta, potatoes, and their derivatives create an ideal environment for Bacillus cereus growth due to their neutral to slightly alkaline pH (6 to 7). The spores are naturally present in raw rice, flour, and potatoes, and are heat-resistant, surviving the cooking process. When these starchy foods are left at room temperature for over 2 hours after cooking, the spores activate into bacteria, multiplying and producing toxins. These heat-stable toxins persist even after reheating. This is particularly concerning for rice and pasta, which can cause severe food poisoning if improperly stored.

2. Dairy Products

Raw and pasteurized milk, cheese, and other dairy products can be contaminated if hygiene is not maintained during production and storage. Bacillus cereus spores can be present in raw milk and survive pasteurization. If pasteurized milk is not refrigerated, the ambient temperature can trigger spore activation and bacterial growth. In dairy products like cheese and yogurt, using contaminated milk or unsanitary equipment during production can lead to Bacillus cereus multiplication.

The presence of Bacillus cereus has also been reported in other foods like meat and vegetables.

Food Poisoning Caused by Bacillus cereus and its Effects on Human Health

Bacillus cereus can cause two major types of gastrointestinal illnesses: emetic (vomiting) and diarrheal. These illnesses result from different toxins produced by the bacterium, each with distinct characteristics and mechanisms.

Emetic illness is caused by consuming food containing cereulide toxin. This toxin is produced at temperatures around 25 to 30 degrees Celsius and is heat-stable, remaining in the food even after cooking. The bacterium does not produce the toxin in the stomach after consumption; the toxin is already present in the food. Emetic illness occurs with lower bacterial doses, around 10³ CFU (colony-forming units) per gram of food. Symptoms like nausea, vomiting, and abdominal pain appear rapidly, within 1 to 6 hours of consumption.  This type of poisoning is usually associated with consuming starchy foods like rice and pasta contaminated with the toxin.

Diarrheal illness usually results from a combination of toxins produced by Bacillus cereus during its activity in the host's body.  It requires higher bacterial doses, around 10⁵ to 10⁸ CFU per gram of food.  In this type, the toxin is produced in the intestine after bacterial growth and activity. Symptoms, including diarrhea and abdominal cramps, typically appear between 6 to 15 hours after consumption. This type of poisoning is mainly associated with consuming dairy products contaminated with the bacterium.

Vulnerable groups to Bacillus cereus poisoning include infants, toddlers, and school-aged children, who usually experience more severe symptoms. However, cases where Bacillus cereus leads to severe or even fatal infections are rare and often overlooked. This type of poisoning is mainly caused by improper handling, storage, and cooling of foods, creating conditions suitable for Bacillus cereus growth and toxin production. These factors are controllable and preventable, and adhering to food hygiene principles can significantly reduce the risk of poisoning.

Methods for Preventing and Controlling Bacillus cereus Contamination

To prevent Bacillus cereus contamination in foods, thorough cooking is essential to eliminate potential bacteria. After cooking, foods should be cooled within two hours and refrigerated (below 5 degrees Celsius).  Cooked foods should never be left at room temperature for extended periods, as this facilitates bacterial growth. When reheating, only the required amount should be heated, and it is best to avoid repeated heating and cooling, which can increase bacterial growth and toxin production.

Raw vegetables should be thoroughly washed and disinfected with clean water before consumption. Vinegar (one part vinegar to three parts water) can be used for disinfection. After washing and disinfecting, vegetables should be rinsed and dried completely before refrigeration, as moisture and ambient temperature can promote microorganism growth.

To prevent cross-contamination, raw foods should be kept separate from cooked foods. After using cutting boards and knives, all surfaces and utensils that have come into contact with food should be thoroughly cleaned. Dairy products like milk should always be refrigerated, and it is best to avoid consuming unpasteurized milk. Other dairy products should also be stored at appropriate temperatures, and expired products should be avoided.

By following hygiene principles in food preparation, storage, and cooking, the risk of Bacillus cereus related illnesses can be minimized. Proper cooking and storage temperatures, thorough washing of food items, and avoiding prolonged storage at room temperature are simple yet effective measures to maintain health.