what is E.coli SEM image of E coli bacteria


E.coli (Escherichia coli), is a type of bacteria that lives in your intestines and those of animals (cattle and poultry). Most types of E.coli are harmless to us and are actually important for our internal gut flora. However, of concern to us are those strains of E.coli that are bad and dangerous to us. Meaning those that can cause diarrhoea if you eat contaminated food or drink “dirty” water.

The Biology of E.coli

Escherichia coli (E.coli) is a gram-negative facultative, anaerobic, rod-shaped bacteria, 2–6 μm long and 1.1–1.5 μm wide. Escherichia coli are usually motile by flagella and produce gas from fermentable carbohydrates.  E. coli is also the most common member of the normal flora of the human intestinal tract. Because E.coli occur naturally in the gut, the most common way that this bacteria causes the infection is by the faecal–oral route. This is also why this bacteria is so common in food poisoning and why we test for E.coli. Poor hygiene and cross-contamination are the major causes of E.coli contamination. It is for this reason, that E.coli is considered as an indicator organism. It tells us that somewhere along the line of production to food preparation, unhygienic practices took place.

Why is E.coli important to test for?

Through unhygienic practices, E.coli is transmitted to humans primarily through consumption of contaminated foods and unwashed hands.

Such foods include raw or undercooked ground meat products, raw milk, and contaminated raw vegetables.

You can become sick when you eat even a small amount of E. coli present in food or water. We know that if E.coli is present in food, water or on the hands of a food handler, there is a very high chance that other dangerous bacteria are present as well.

Among the ways this can happen:

  • Ground meat (mince):
    • Eating mince that carries E. coli, usually from and the meat wasn’t cooked well enough to kill the bacteria.
    • When meat is processed, the bacteria from the animals’ intestines make their way into the meat. This happens more with mince than we steaks because it comes from more than one animal.
  • Raw or untreated milk/dairy:
    • Drinking unpasteurised milk, which hasn’t been heated to kill bacteria. E. coli can get into the milk from the cow’s udder or from milking equipment.
  • Vegetables and fruit:
    • Eating fresh vegetables or fruit that’s been tainted by water that has the bacteria. This happens most often when manure from nearby animals mixes with the water supply.
    • This is why is so important to wash and sanitise fruits and vegetables before preparation.
  • Water:
    • Untreated water carries a high risk of E.coli contamination.
  • Food Handlers:
    • Food handlers that do not wash their hands after using the loo or handling raw foods can contaminate anything they touch. This is why frequent hand washing is so important.

You can also contaminate food in your own kitchen if you allow a knife or cutting board that has touched uncooked meat (like chicken) to come into contact with food that will be eaten raw or uncooked (like a salad).

Symptoms of E.coli Food Poisoning

Signs and symptoms of E. coli infection typically begin three or four days after exposure to the bacteria, though you may become ill as soon as one day after to more than a week later.

Signs and symptoms include:

  • Diarrhoea, which may range from mild and watery to severe and bloody
  • Abdominal cramping, pain or tenderness
  • Nausea and vomiting, in some people

E.coli 0157:H7

The worst type of E. coli, known as E. coli O157:H7, causes bloody diarrhoea and can sometimes cause kidney failure and even death.

Strains of E. coli

There are a large number of strains of E. coli. Laboratory strains are somewhat atypical when compared to strains isolated from the gut of animals or humans or from the environment. The natural strains contain more genes than the laboratory strains. About 2,000 genes make up the core genome, which consists of those genes which any strain of E. coli must have to live and grow. The remainder of the genes varies between strains (there are more than 15,000 different genes that have been found in different strains)1. Genes found in only some strains include genes involved in pathogenesis and in survival in a mammalian host. This variable genetic make-up means that different strains of E. coli cause different diseases. Thus, there are diarrheagenic E. coli (DEC), uropathogenic E. coli (UPEC), and E. coli which cause meningitis. In this article, I will focus on the DEC strains.

Prevention of E.coli contamination

Fortunately E.coli contamination is very easy to prevent. Following the basic hygiene and food safety rules will help prevent causing any further contamination in your kitchen or food factory.

  1. Always practice good personal hygiene.
    1. This means washing your hands after handling raw foods
    2. After going to the toilet.
  2. Store raw meats and vegetables separately
    1. Keep raw foods separate from all ready to eats foods.
    2. This can mean, keeping these foods in sealed containers and storing raw foods below ready to eats.
  3. Cook raw foods to above 70°C for a minimum of 10 minutes.
  4. Display hot foods above 60°C.
  5. Wash and sanitise all fruits and vegetables before use.
  6. Cleaning and sanitise cutting boards, equipment and tables before and after using them.

Following these steps as set out in the FCS hygiene audit will help prevent possible food poisoning cases.

Food Consulting Services is a private South African-owned Food Testing Laboratory and Food Safety Consultancy, that tests water and food to ensure compliance with South African National Standards. We also perform hygiene survey audits to the hospitality and food manufacturing industry. If you’d like to learn more about Food Consulting Services, visit our website or feel free to enquire with us. We look forward to hearing from you and becoming your food safety partners. Get in touch with us for more information.

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