Saturday, 12 December 2020

E.coli Producing Shiga Toxin, Infection and Food poisoning

  We have all had food poisoning, and it’s the worst. Stomach cramps, diarrhea, nausea, not being able to keep any food down, maybe a fever… these are all symptoms of food poisoning, which means the consumption of contaminated food or drink. When it comes to stomach trouble, it’s not always easy to identify what in particular is causing the symptoms.

The term “gastroenteritis” refers to inflammation of the lining of the gut, particularly the stomach and intestines, and cases of gastroenteritis can be caused by viruses, bacteria, or parasites. When it’s clear, or at least likely, that the source of an infection is contaminated food, we call it food poisoning.

It turns out that most cases of food poisoning clear up on their own without any type of treatment required. However, one of the most serious complications of food poisoning is dehydration, which can be especially deadly for those that are very young or very old.

Food poisoning can be caused by a variety of pathogens, i.e. Staphylococcus aureus, Clostridium,
Norovirus,
Salmonella,
Listeria,Vibrio, or
Campylobacter.

Here we’re going to discuss  about one notorious cause of food poisoning in particular, the one you usually hear about in the news: Shiga toxin-producing
E.coli, or STEC.

  E.coli consists of a diverse group of bacteria belonging to the Enterobacteriaceae family, which are associated with diseases ranging from UTIs to respiratory illness to meningitis. Pathogenic strains of E.coli can be categorised into what are called “pathotypes.” In particular, there are six pathotypes associated with diarrhea, which are appropriately named “diarrheagenic E.coli.”

six pathotypes type diarrheagenic E.coli :
1) Shiga toxin-producing E.coli,or STEC.
2) Enterotoxigenic E.coli, or ETEC.
3) Enteropathogenic E.coli, or EPEC.
4) Enteroaggregative E.coli, or EAEC.
5) Enteroinvasive E.coli, or EIEC, and
6) diffuselyadherent E.coli, or DAEC.
  These bacteria are gram-negative. They’re facultative anaerobic rods, which means they can survive both with or without oxygen present, and they contain lipopolysaccharide.

The Shiga toxin-producing E.coli cause disease by producing a toxin called Shiga toxin, and here is where it gets more confusing. Shiga toxin-producing E. coli are sometimes also called verocytotoxic E.coli, or VTEC, or enterohemorrhagic E.coli, or EHEC.

In the United States, the most common serotype of STEC is E. coli O157:H7, which is the type they are usually talking about on the news, like when there’s a widespread romaine lettuce recall. An infection begins when you swallow STEC, meaning that you have gotten a microscopic amount of human or animal feces in your mouth. That may sound gross, but it happens a lot more than you think.

Common sources include raw milk, contaminated water, or contaminated food. Foods that are considered high risk for E.coli O157:H7 include unpasteurized apple cider, soft cheeses made from raw milk, and sometimes undercooked beef or contaminated lettuce.

However, sometimes people get infected by touching surfaces at petting zoos, swallowing lake water while swimming, or eating food prepared by someone who didn’t wash their hands after using the bathroom. In most cases, STEC infections have an incubation time of 3 to 4 days before symptoms set in.

Pathogenesis of Shiga Toxin:

  STEC strains, as their name suggests, express a Shiga toxin that is one of the most potent bacterial toxins known. Shiga toxins consist of two major subunits, A and B, which work together to damage cells in the gut. In particular, these toxins disrupt protein synthesis in healthy cells and cause destruction of intestinal microvilli, which are finger like projections that typically help healthy cells absorb nutrients.

As a result, approximately half of patients experience vomiting, and a significant portion experience bloody diarrhea and severe abdominal pain. In some cases, Shiga toxin can trigger an over reaction of the immune system to attack healthy cells, as well.

Diagnosis

For the most part, STEC infections are diagnosed by testing stool specimens in the lab. In the case of big outbreaks, identifying the specific strain of STEC is important, so that we can track when and where each strain was found, and where it might be spreading. Public health officials suggest that anyone experiencing diarrhea for more than three days, especially if accompanied by vomiting and high fever, contact their healthcare provider to get checked out.

Hydration is the most important treatment, as antibiotics are not typically prescribed for this kind of infection. In fact, antibiotics can make the illness worse, causing patients to be at higher risk for hemolytic uremic syndrome, or HUS. HUS is a complication for a small subset of patients that can cause renal failure and other deadly symptoms.

Precautions 

Ultimately, the best thing you can do is wash your hands often, be careful about what you’re eating, make sure to cook meat thoroughly and avoid raw or unpasteurized milk or dairy products, do your best to avoid swallowing lake or pool water, and make sure to keep food preparation areas immaculately clean. With any luck, you can avoid food poisoning for good. 

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