On August 24, 2022, the Spanish Agency for Food Safety and Nutrition (AESAN) established a food alert for staphylococcal toxin poisoning in a glass canned product, specifically, mushrooms fried in olive oil. Although the initial alert affected only one manufacturer, two days later it was extended to a total of six brands that shared the same batch number [02/02/2021].
There is a belief that, in the face of such an alert, cooking the product at high temperatures may be sufficient, since all bacteria die during the cooking process. But it is not always so simple; in this case, neither boiling, roasting nor even frying the contaminated product guarantees its safety . In staphylococcal toxin poisoning, it is as easy to get poisoned with the cooked product as it is raw.
Where does staphylococcal toxin come from?
Staphylococcal toxin is a single chain protein, synthesized by Staphylococcus aureus . It is a facultative anaerobic bacterium, it does not need oxygen in its metabolism, but it can live in environments with oxygen and use it if it is present.
It inhabits both the skin and the mucous membranes of some people, without causing problems, since the epidermis works as an effective barrier. It is estimated that about 20% of the population are persistent carriers of this bacterium, and another 60% may be occasional carriers. In sensitive people it can cause minor skin infections. But the fact that its presence on the skin or mucous membranes is practically harmless does not make it a harmless bacterium.
When food is handled with bare hands —and even more so if the handler touches their face or hair—, it is easy to deposit S. aureus in that product. If the consumption is immediate or in a short time, or if the food is cooked after handling, the bacteria will die in the process and surely nothing will happen.
However, if after handling the product is left in an environment with a temperature between 10 and 50 °C, bacteria can proliferate in the food and contaminate it.
staphylococcal toxin poisoning
The production of staphylococcal toxin is directly associated with the proliferation of S. aureus . It is the toxin, not the bacteria, that causes diet-related health problems. Cooking the food after this proliferation kills the bacteria, but does not solve the problem of contamination, since one of the characteristics of this toxin is its high stability even at high temperatures. In other words , the toxin is not degraded by cooking, frying, or baking .
We must banish the erroneous idea that “heat kills everything”.
Some of the symptoms of staphylococcal toxin poisoning include hypersalivation, nausea, vomiting, abdominal cramps, and diarrhea. If it continues over time without proper attention, it can lead to dehydration and hypotension. The intoxication is generally self-limited; the patient recovers in an average of 20 hours from the start, and on very rare occasions it takes more than 48 hours. However, in sensitive patients such as the elderly, babies or immunocompromised people it can have very serious consequences.
In most cases, poisoning is caused by food that has already been cooked, and therefore, the bacteria responsible for the toxin are no longer there. Antibiotics are discouraged , in addition to the fact that there are no more bacteria, mainly for two reasons: firstly, because they can negatively affect the intestinal microbiota and aggravate digestive symptoms; and secondly, because due to the indiscriminate abuse of antibiotics, more and more bacterial strains are resistant to these antibiotics.
It is better prevent
To avoid food poisoning by staphylococcal toxin there are several techniques, which are basic in food handling. Each one, by itself, is already useful, and combining them all, a scenario practically free of intoxication is achieved.
On the one hand, maintain a very scrupulous hygiene at all times of food production. Thorough hand washing with soap and water removes most S. aureus from the skin, but special care must be taken not to touch the mouth, nose, face or hair during the food preparation process. Of course, it is a priority to work with the hair collected and covered.
On the other hand, proper food preservation is also essential. If the handled product is not going to be cooked or consumed immediately, the best thing to do is refrigerate or freeze the product and avoid breaking the cold chain by all means. S. aureus cannot grow below 10°C. It is important to remember that cold slows or stops growth, but does not kill bacteria. The Scientific Committee of the AESAN recommends the ideal temperature for the conservation of refrigerated food between 0 and 5 °C
Some cooked foods, consumed hot, lose organoleptic properties when cooled and reheated. These foods can be kept hot. The AESAN Scientific Committee recommends, for hot storage, using constant temperatures of at least 63 °C . Any conservation at a lower temperature does not guarantee the death of staphylococci, and below 50 °C they can proliferate massively and contaminate the product.
If it is not going to be kept hot, again, refrigerating the product is the best option; the cooling process must be as fast as possible, to avoid bacterial growth while the food loses temperature. Specifically, it must reach a temperature of 4 °C in less than two and a half hours , and when reheated it must reach a minimum of 74°C for at least 15 seconds.
References:
AESAN. 2022. Alert for staphylococcal toxin poisoning in mushrooms fried in olive oil (Boletus edulis) from Spain (Ref. ES2022/248).
Argudín, M. Á. et al. 2010. Food Poisoning and Staphylococcus aureus Enterotoxins.
Toxins, 2(7), 1751-1773. DOI: 10.3390/toxins2071751
AESAN Scientific Committee (Working Group). 2021. Report of the Scientific Committee of the Spanish Agency for Food Safety and Nutrition (AESAN) on the time-temperature combinations necessary for the safe cooking of food and the appropriate temperatures for keeping hot and reheating prepared meals. Magazine of the Scientific Committee of the AESAN, 33, 113-150.
Figueroa G, G. et al. 2002. Carriage of enterotoxigenic Staphylococcus aureus in food handlers. Medical Journal of Chile, 130(8), 859-864. DOI: 10.4067/S0034-98872002000800003
Kadariya, J. et al. 2014. Staphylococcus aureus and Staphylococcal Food-Borne Disease: An Ongoing Challenge in Public Health. BioMed Research International, 2014, e827965. DOI: 10.1155/2014/827965
