Petri dish representing an E. coli culture and hand in lab gloves

E. coli: infections under the microscope

Gemma King Learn more, Research, Treatments

Escherichia coli (E. coli), is a type of bacteria that occurs in the intestines of people and animals, often without causing any problems at all. But in some cases it causes illnesses ranging from mild (acute diarrhoea) to life-threatening (haemolytic-uremic syndrome and severe bacteraemia). One study demonstrates that E. coli caused fatal diarrhoea in nearly 60,000 people in 2016, globally.

It is also able to survive in the environment, such as in water and soils (which is why it is so important to wash fruit and veg before eating it raw). Most strains are completely harmless, but E. coli is known for being a major cause of severe food poisoning (also called a gastrointestinal [GI] infection, or gastroenteritis). That is usually due to a particular type (a strain) called 0157. Find out more about E. coli as a cause of food poisoning.

This bacteria can also cause serious infections when it gets into vulnerable areas of the body, such as wounds, catheter sites or into the bloodstream. It is a leading cause of urinary tract infections, too. This blog explains the basic biology of E. coli, as well as the causes, symptoms, treatments and outcomes of infections.

Basic biology of E. coli bacteria

E. coli is a gram-negative (i.e. it is not stained by Gram stain) rod-shaped bacterium. Each cell is 1-2µm (micrometres, or microns) in size – 400 million bacteria would fit on a full stop. This is far, far smaller than can be seen with the naked eye. E. coli is a ‘facultative anaerobe’, which means that it thrives in oxygenated environments, but can also survive in environments that lack oxygen, such as the gut.

Some strains of E. coli have flagella, which are whip-like appendages that they can use to move through liquid or semi-solid environments. Not all bacteria are able to move like this, so it provides it with a great advantage. Many strains are also able to stick to the surface of intestines, and other surfaces inside the body.

Aside from its ability to cause different types of infection and to survive in a range of environments, this bacterium also reproduces very rapidly. Each cell can divide into two new ‘daughter’ cells every 20 minutes in favourable conditions. Each time a cell divides, there is the opportunity for a fault in the process to result in a ‘mutation’ in the genetic code, meaning that one of the daughter cells might not be a perfect copy. Most of the time these mutations either cause the cell not to function properly, or they have no discernible impact. Sometimes, however, they cause that cell to become resistant to a medicine such as antibiotics. Being able to divide rapidly means that these resistant mutations have more opportunities to occur. On average, one natural mutation that gives antibiotic resistance occurs per 100 million offspring per generation.

Mechanisms of illness

There are six different ways that E. coli is believed to cause illness:

  1. Enterotoxigenic (producing toxic chemicals), as in Traveller’s Diarrhoea.
  2. Enteropathogenic, as in the cause of childhood diarrhoea.
  3. Enteroinvasive, as in E. coli-induced dysentery.
  4. Enterohaemmorhagic, as in haemorrhagic colitis or haemolytic-uremic syndrome.
  5. Enteroaggregative, as in the persistent childhood diarrhoea found in developing countries.
  6. Enteroadherent, as in childhood diarrhoea and traveller’s diarrhoea in Mexico and North Africa.

E. coli bacterial infections

E. coli infections cause many illnesses, such as meningitis, pneumonia, cholecystitis, cholangitis, intra-abdominal abscesses, enteric infections, simple or recurrent cystitis, pyelonephritis and sepsis. A 2019 study found that hospital stays lasted longer in people with drug-resistant E. coli than in those with drug-susceptible strains, although resistance did not increase mortality. The researchers estimated that E. coli bacteraemia cost the UK £14 million (in 2012 £s). Research has also shown that preventing unnecessary catheterisation could reduce the cost of catheter-associated infections (urinary tract and bloodstream) significantly; they directly cost UK hospitals more than £50 million in 2016/17.

Worldwide, diarrhoeal disease caused more than 1.6 million deaths in 2017; sadly, one-third of those that died were children. While things are improving (in 1990, 1.7 million children died from diarrhoeal diseases), and not all of those deaths are caused by E. coli, it highlights the devastation that it can cause. Even in the UK, such diseases killed three infants and nine 1-4 year olds in 2019 (and a total of 1,419 people altogether). You can use this tool from the Global Health Data Exchange to explore data on deaths by cause, age, country and more.

Since the start of the COVID-19 pandemic, the number of cases of E. coli bacteraemia reported in hospitals in England has decreased. This could be for a number of reasons. For example, fewer people are acquiring healthcare-related infections as all elective surgeries were cancelled. It is possible that E. coli infections were tested for less frequently due to reduced staffing of lab facilities, or that hospital staff and patients are washing their hands more frequently.

Hospitals in England reported more than 37,000 cases of E. coli bacteraemia in 2020 (compared with nearly 44,000 during 2019).

Latest data:

There were 3,245 E. coli bacteraemia reported by hospitals in England during March 2021, compared with 3,013 during March the previous year. However, monthly numbers have fluctuated rather than increased consistently throughout the intervening months.

According to the NHS, the following things put you more at risk of contracting an E. coli infection (of the bloodstream, a wound or in the urinary tract):

  • Having a urinary catheter or intravenous line
  • Dehydration
  • Older age
  • Prostate issues
  • Gall bladder or kidney stones
  • Chronic (long-term) health conditions such as COPD and diabetes
  • Open wounds, like ulcers
  • Recent hospital admission
  • Recent surgical procedure

Things like eating unwashed fruit and vegetables, eating raw or poorly cooked meats and not washing your hands during food preparation and eating put you more at risk of getting a GI E. coli infection.

The illnesses caused by E. coli are often the result of the toxins (harmful chemicals) that they produce. Not all strains produce toxins, and the ones that do must be present in significant numbers to produce enough toxin to make you sick.

Some examples of the toxins and/or illnesses produced by different strains include:

  • Verotoxigenic E. coli (also known as 0157) produces vero-cytotoxin, which ruptures red blood cells, leading to haemolytic uraemic syndrome (HUS) and kidney failure. There is no evidence that antibiotics improve the course of this illness.
  • Enterotoxigenic E. coli (ETEC) is a strain – or group of strains – that produce special toxins that stimulate the lining of the intestines to secrete excessive fluid and cause diarrhoea. It is the main cause of both Travellers’ Diarrhoea and diarrhoeal disease in children in low-income countries.

What causes E. coli infections?

The reason that some strains don’t cause illness is that they do not produce the toxins described above in high enough volumes to do so. But where are the harmful strains found? E. coli exists in so many different environments that it has been hard to pinpoint any one source that contributes the most. Traditionally, we think of it as a type of food poisoning caused by gone-off meat or poor food hygiene at restaurants. However, recent research found that most infections with antibiotic-resistant E. coli were caused by strains typically found in humans, and that non-human ‘reservoirs’ made little contribution to invasive illness in people.

Diagnosis of an E. coli infection

The symptoms vary depending on the type of infection. For example, in someone with a UTI it may cause the following:

  • Generally feeling unwell
  • Fever and/or rigors (shakes)
  • Altered mental state
  • Reduced mobility
  • Headache
  • Pelvic and/or loin pain
  • Excessive frequency in passing urine
  • Burning sensation when passing urine
  • Offensive smell or colour or urine
  • Haematuria (blood in the urine)

However as food poisoning (a gastrointestinal [GI] infection, or gastroenteritis) the symptoms might be:

  • Diarrhoea (which may or may not contain blood)
  • Nausea and/or vomiting
  • Stomach cramps
  • A fever
  • Dehydration

GI infections can, rarely, lead to a serious condition called haemolytic uraemic syndrome, which can cause kidney failure and death. This is most common in children under the age of five years.

Treatments and outcomes

The treatment depends on the strain of E. coli and the type of infection (GI, UTI or bloodstream). Antibiotics are often not recommended for GI infections as they can cause complications such as infection with Clostridium difficile after treatment. There is no evidence that antibiotics help with infections caused by E. coli 0157. Drink lots of water to replace that lost through vomiting and diarrhoea.

Some strains of E. coli are resistant to the most commonly used antibiotics. For example, β-lactams are a type of antibiotic. There is a type of E. coli called ‘ESBL producing’, which stands for extended spectrum β-lactamase. This means that the bacteria produce an enzyme (lactamase) that breaks down the antibiotic (lactam). As a result, these antibiotics are not effective against ESBL E. coli. However, in some cases, another medication called sublactam can be given, as it prevents the bacterial enzyme from working, allowing the antibiotics to work.

If you have persistent bacteraemia (a blood-stream infection) you will likely need medical treatment with antibiotics.

Do you, or someone you know, have an antibiotic-resistant infection? You can contact our Patient Support Service for free information and a friendly chat.

Preventing the spread of E. coli

Although the infection is contagious, it is possible to live safely with someone who has an E. coli infection. Hospitals isolate people with the infection due to the double threat of exposing vulnerable sick people to an infection that is hard to treat.

If you have a GI infection (stomach bug) caused by E. coli, it is very important to ensure good hand hygiene, and if possible to use separate washing and toilet facilities throughout the duration of your illness. Most GI infections like this will not need treatment.

If you have a chronic (long-term) infection, particularly with a resistant strain of the infection, you may be advised to use separate washing and toilet facilities to other members of the household whenever possible. Everyone you live with will need to maintain good hand hygiene, too.

The best way to avoid getting a E. coli infection is to wash your hands thoroughly and regularly, particularly after going to the loo, and follow our tips to prevent the spread of antibiotic resistance. These apply to preventing the spread of all types of bacterial infection.

Current relevance

Professor Colin Garner, CEO of Antibiotic Research UK, explains: “E. coli is a rapidly evolving bacterium that has a variety of uses within healthcare, such as in drug production. Sadly, it is also the cause of hundreds of thousands of hospitalisations every year. Its ability to adapt and resist treatment makes it a particularly dangerous bacterial infection. It is vital that we continue to invest in research and the development of new drugs that will help us stay one step ahead of it.”

Further information

Some sources we recommend if you wish to know more:

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