The bad side of E. coli: urinary tract infections

Escherichia coli, better known as E. coli, is a tube-shaped microbe that sometimes causes infection. E. coli is notoriously at the root of urinary tract infections (UTI) when it travels to the urinary tract.

This is a case of ‘wrong place, wrong time’, where the usually harmless microbe ends up where it’s not supposed to, finds a new home and leads to illness. Some strains, or types, of E. coli take on this role of opportunistic pathogen, causing infections like UTIs.

UTIs are common in the UK and most are treatable with antibiotics. But the problem of antibiotic resistant UTIs is increasing. Here at the Quadram Institute, we’ve researched the antibiotic-resistant strains of E. coli causing UTIs in our region of Norfolk, UK.

The worst side of E. coli: food poisoning

Other strains of E. coli can cause food poisoning. Though E. coli is not the only microbe that causes food poisoning – others include Campylobacter and Salmonella – it’s a particularly nasty infection. In 2024, an outbreak of E. coli infected nearly 300 people and hospitalised over 100, though the root cause of the outbreak was not identified.

These outbreaks are caused by very specific strains of E. coli called STEC, which stands for Shiga-toxin producing E. coli. The toxin produced by STEC can make you ill, with symptoms like diarrhoea, cramps and vomiting. In severe STEC cases, this can lead to a kidney condition called haemolytic uremic syndrome, which has lifechanging effects.

While these cases of E. coli are dangerous, the causal strains are rare and there are ways to protect yourself from this microbial risk. At home, you can follow guidance from the Food Standards Agency by cooking food properly, rinsing fruits and vegetables eaten raw and washing your hands to prevent contamination from raw animal products onto fresh produce and surfaces.

The Food Safety Research Network, hosted here at Quadram, also works with food businesses, testing labs and the government to develop better testing for STEC.

But there are many of other strains of E. coli, not just the bad strains.

A model microbe with so much genetic diversity

E. coli is very well studied. Firstly, because it’s a useful model organism in biological research to learn about genetics at the molecular level. Secondly, because of how genetically diverse this microbe is.

Recent PhD graduate, Gab Astorga, uncovered some of E. coli’s genetic diversity during his project. Gab monitored E. coli strains found in retail foods like poultry, shellfish and leafy salads. He found that the majority of E. coli strains on these foods are commensal, which means they don’t do much harm nor good to humans.

He found that these foods contain many different strains of E. coli carrying different antimicrobial resistance markers, which could be useful in identifying potential food threats.
Gab explains, “Two strains of E. coli can be as genetically different, if not more different, than a human to a chimpanzee”.

It’s this diversity, in part, that means many E. coli strains can contribute to good health.

The good side of E. coli: a key signature of the gut microbiome

Before occasionally reaching the urethra, commensal E. coli lives in the intestinal lining. It’s in your intestines that E. coli spends most of its time contributing to the community of microbes which ensures your health and wellbeing – your gut microbiome.

Present early on during infancy, these E. coli strains are an important gut microbe. They are part of the Escherichia microbial ‘signature’, one of five microbial ‘signatures’ that represent the different groups of microbes working together in the gut.

Commensal E. coli can use oxygen to create the anaerobic environment many other beneficial gut microbes need to thrive, like the probiotic Bifidobacterium. Together, these gut microbes break down our food to release beneficial compounds such as short chain fatty acids, which have protective qualities.

Vitamin factories

Commensal E. coli also produce important vitamins like vitamin K, the group of vitamins necessary for wound healing and maintaining healthy bones. More recently, E. coli was used to make vitamin B12, a key micronutrient that helps produce red blood cells. The vitamin B12 industry is currently thriving and pharmaceuticals treating B12 deficiency have high commercial value.

But B12 production using bacteria is complex and releases a lot of waste cobalt, which is hazardous and costs money. Our researchers from the Warren group and national collaborators engineered E. coli, which don’t naturally produce the vitamin, to make vitamin B12 while reducing cobalt waste. Specific E. coli now present an option for the industrial production of an important micronutrient.

Like many living organisms, E. coli is complex. Some strains of E. coli are good for you most of the time when they contribute to a healthy, balanced gut microbiome but other strains can be bad for you if they reach the wrong place at the wrong time.