STEC, Shiga-toxin producing Escherichia coli. The recent recall of a batch of sliced scamorza cheese provides an opportunity to learn more about this bacterium. (1)
The jambs of E. coli capable of producing shiga-toxins are among the most dangerous food-borne bacteria. As capable of causing particularly severe and sometimes lethal clinical forms especially in the most at-risk consumers (children and the elderly).
STEC, the bacterium and its consequences for consumer health
STEC Escherichia coli are able to adhere firmly to the cells of the intestinal epithelium and produce potent toxins, so-called Shiga-like toxins, precisely. Which enter the circulation and exert their action on target cells far from the intestinal tract. Namely, the endothelial cells lining the vessels of the renal glomeruli and the small blood vessels of the colon.
STEC infections are therefore characterized by diarrheal episodes sometimes complicated by intestinal bleeding (hemorrhagic colitis). And in severe cases, from acute renal failure related to dysfunction of the renal glomeruli. The actual failure is aggravated by concomitant hemolytic anemia and platelet deficiency, which combine to delineate the severe picture of the so-called Hemolytic-Uremic Syndrome (HUS).
SEU and hemorrhagic colitis can result in a lethal outcome, or otherwise cause serious illnesses such as chronic renal failure, with possible need for dialysis treatment and recourse to kidney transplantation. The severity of the disease leads public health authorities to the utmost severity in cases of STEC-contaminated food products.
STEC, dairy and meat products
Several animal species – ruminant, in particular – harbor E. coli Shiga-toxin producers in the intestines without presenting any symptoms of disease. Animals in this case behave as ‘asymptomatic carriers’. And their milk, or meat, may enter the food chain where not subject to targeted testing.
Cheeses, when subject to recall, present a greater hazard because they are foods that do not undergo heat treatment before consumption (foods ‘Ready-to-Eat‘). Heat treatments above 70°C-such as pasteurization or boiling of milk and complete cooking of meat-are conversely effective in destroying the jambs of E. coli Shiga-toxin producers.
Thus, STEC contamination of a cheese can result from the raw material (milk), but it can also occur downstream in the production process. This is the case of ‘post-process’ contamination, which can take place despite the fact that hygiene control procedures are followed (supplier control, milk pasteurization, production process hygiene), thus in spite of their apparent adequacy.
The ‘post-process’ contamination, in particular, can be blamed on the colonization of equipment – in the industrial or distribution stage (e.g., portioning or packaging machines) – by microbial strata capable of forming tenacious microbial films, commonly called ‘biofilms,’ where bacteria are produced by the action of disinfectants used in sanitization practices. The ability to form biofilms is indeed characteristic of several bacteria, including the E. coli Shiga-toxin producers.
STEC, operator responsibilities and corrective actions to be taken
The food handler (FBO) is primarily responsible for placing food on the market that does not pose a health risk to the consumer. (2) This responsibility is joined by that of downstream operators in the supply chain, namely the distributor.
The implementation of hygienic measures (GMP, GHP) and the ubiquity of analytical controls in the plant and distribution-including the detection of any niches colonized by biofilm-producing bacteria-are confirmed to be essential for reducing the microbiological risk of food safety.
STEC-contaminated foods-according to the requirements of the ‘General Food Law‘-must be classified as seriously hazardous to public health and then subjected to the most drastic corrective measures. (3) In implementation of current European rules, there are no tolerable microbial limits and the mere presence of STEC, even at minimal levels, is sufficient to trigger alerts on all batches of product potentially involved.
Silvia Bonardi and Dario Dongo
Notes
(1) Recall Società Agricola F.lli Ponti, product formaggella 2.5 kg, production lot no. 06-28.8.18, reason for reporting presence of E.Coli STEC. Notification 3.10.18, on the Ministry of Health website.
(2) For more on this topic, please refer to our free ebook ‘Food safety, mandatory rules and voluntary standards‘, at https://www.greatitalianfoodtrade.it/libri/sicurezza-alimentare-regole-cogenti-e-norme-volontarie-il-nuovo-libro-di-dario-dongo. For updates on the evolution of the international reference standard, ISO 22000:2018, see the article https://www.greatitalianfoodtrade.it/certificazioni/iso-22000-2018-lo-standard-aggiornato-per-la-sicurezza-alimentare
(3) See reg. EC 178/02, Articles 14 and 19. Among the corrective actions to be taken, when the unsafe product has already reached the level of distribution to the consumer and ‘any other measures are inadequate to ensure public health‘, public recall should be carried out
Graduated in Veterinary Medicine and Specialist in Inspection of Food of Animal Origin and in Veterinary Public Health, she is Professor of Inspection and Control of Food of Animal Origin at the University of Parma.
Dario Dongo, lawyer and journalist, PhD in international food law, founder of WIISE (FARE - GIFT - Food Times) and Égalité.
