Due to emerging trends in consumption habits, the presence of Cereulide toxin in food constitutes an emerging risk, as although the danger is known, an increase in exposure can be expected in the future. The development of analytical techniques for quantifying this toxin, produced by certain strains of Bacillus cereus, is therefore an essential tool for its control in food matrices.
Bacillus cereus is a group of ubiquitous bacteria, widely spread in the environment, especially in soil. We can find B. cereus spores in a large number of foods, such as milk, vegetables, cereals, flours, spices and herbs, texture agents, and liquid eggs…
Bacillus cereus: Symptoms and Causes
Some strains of B. cereus pose a risk to food safety as they can cause two types of human illnesses:
- Intoxication with emetic symptoms, caused by the ingestion of the toxin that these strains can produce, Cereulide toxin. This is a heat-stable peptide toxin produced, as we mentioned, by cereus. From ingestion, the incubation period is 30 minutes to 6 hours, resulting in nausea, vomiting, intestinal cramps, and general discomfort. Symptoms typically last less than 24 hours and it is not a communicable disease (as it has been caused by a toxin). The toxin affects various types of human cells and in some cases can lead to serious complications, such as reversible liver failure.
- Toxinfection with diarrheal symptoms, caused by the ingestion of cereus and the subsequent production of Cereulide toxin in the affected individual’s intestinal tract. In this case, symptoms include diarrhea, intestinal pain, typically lasting around 24 hours, it is also not transmissible, and complications are rare.
How Bacillus cereus bacteria are produced
In addition to contamination that can come with raw materials, it can also occur during processing in the production plant, as Bacillus cereus spores are very resistant on surfaces of facilities and equipment. Furthermore, Bacillus cereus has the ability to form biofilms, making it particularly persistent as it can withstand cleaning and disinfection processes.
During processing, spores of emetic strains (those that produce the toxin) become dominant as they have greater heat resistance than non-emetic ones. In canned products where the product is treated at high temperature and when the pH is low, spores can be eliminated, but in other types of foods with less aggressive thermal treatments or without them, there are no means to eliminate them from the food.
Even when the bacteria have been eliminated, if the toxin has been produced in the products, thermal inactivation is not possible without completely destroying the food matrix. Cereulide is not inactivated by baking or cooking treatments commonly used. Furthermore, it is stable in pH ranges between 2 and 11; and due to its small size, technologies used, for example, in the dairy sector such as bactofugation or ultrafiltration, are also ineffective.
In conclusion, although hygiene measures are effective in minimizing the likelihood of B. cereus entering and establishing in the plant, if this occurs, it will be difficult to completely eliminate B. cereus spores from it. On the other hand, as we have discussed, if the bacteria have already produced the toxin, we will face the impossibility of inactivating or eliminating it from the food, even if we could eliminate the bacteria. Therefore, all measures aimed at preventing the production of the toxin in the food become important here.
Bacillus cereus, How to Prevent Food Poisoning?
Temperature control is the primary tool we have to prevent the production of toxin in our products. During the time they remain in the plant, intermediate storages (between different processing operations) are the stages we must control most closely. If the food is kept at temperatures that allow the spores of Bacillus cereus to germinate, bacterial proliferation will occur rapidly, as well as the generation and accumulation of the toxin. Thus, the time of intermediate storage, temperature, and initial bacterial load are the factors that will determine the safety of this stage, as they will influence not only bacterial proliferation but also toxin generation.
In most recorded outbreaks, the importance of not respecting adequate temperatures during preparation and especially food storage has been evident. We know that emetic strains (those that produce the toxin) are not usually dominant in uncooked products or before a thermal treatment. However, once this has occurred, since the spores of these strains are heat-resistant and competitive microflora disappears, germination and rapid bacterial proliferation can occur, resulting in the generation and accumulation of the toxin. The way to avoid this situation is rapid temperature reduction of the food and storage at temperatures below 10°C (preferably between 4°C and 6°C) or above 65°C if storing hot.
Inadequate handling of storage temperatures has been found to be related to the majority of outbreaks occurring in restaurants or other collective catering services. Given the current trend towards the consumption of precooked meals, Cereulide must be considered an emerging threat to the food industry. It should be noted that the problem can also occur in consumers’ homes, so these temperature control measures should also be taken into account in households. Therefore, it is important to provide consumers with good information and training. Regarding risk in product manufacturing, dairy, cereals, and frozen precooked foods are some of the highest-risk products.
Regarding analytical control of products, microbiological methods, suitable for determining the presence or quantification of bacteria, are not logically applicable to the determination of toxin presence (as we can find the latter in food without the presence of the bacteria).
Aware that the presence of Cereulide toxin in food constitutes an emerging risk (known, but one that may be expected to increase due to new consumption trends), AINIA has developed and validated a quantification method based on liquid chromatography coupled to a mass detector (LC-MS/MS). This is the most specific and sensitive accessible methodology for this determination. With this, we continue to expand and complete our portfolio of analytical services, in order to meet the new needs of the food sector.
