New research sheds light on E. coli spread in human communities

Bacteria that often cause urinary infections can spread as rapidly as swine flu. But E. coli that are resistant to several classes of antibiotics behave differently.

Escherichia coli (E. coli) are the most common cause of urinary tract and bloodstream infections worldwide. Many patients are therefore treated with antibiotics, but several variants of E. coli have become multi-drug resistant, which limits available treatment options and poses a major threat to public health.

For this reason, we wanted to understand how quickly new variants of E. coli spread in the human population. Our findings provide further impetus to decipher the fundamental genetic drivers of variation in transmissibility."

Jukka Corander, Professor, Institute of Basic Medical Sciences, UiO

Of note, he says that their research in this project is not considering those types of E. coli that cause a food poisoning, which typically results in symptoms like vomiting, diarrhoea and fever.

More difficult to find out how infectious bacteria are

In recent years, we have had pandemics caused by viruses, such as covid and swine flu. The key tool of epidemiologists is to measure the transmissibility of a virus by a so called basic reproduction number, R0 for short. However, estimating R0 for bacterial pathogens is far more complicated and rarely done.

'Whereas viral infections will typically quickly lead to noticeable symptoms, opportunistic pathogenic bacteria such as E. coli can live even up to several months in the gut without causing any problems. It is only when they relocate to other parts of the body that are normally sterile, such as the bloodstream, that they cause an infection', says Corander.

Most people who get colonized by these bacteria do not fall ill

In a new study published in Nature Communications, scientists have estimated the basic reproduction number (R0) of E. coli for the first time in a human community setting. R0 indicates how many other people an average individual will infect in a population with no immunity or infection control measures in place.

The researchers gathered data from many patient samples in Norway and the UK and studied three closely related genotypes of E. coli. These three types began spreading at the beginning of the 2000s and all belong to the same main type ST131, which was discovered in 2008, after it had already caused a worldwide pandemic. Because the ST131 causes such a large number of urinary and bloodstream infections, it has been a focus of international attention for scientists ever since it was first detected.

'What we found was that one type, ST131-A, spread as rapidly as certain viruses that have caused major outbreaks worldwide, such as the swine flu (H1N1). That was quite surprising, for whereas swine flu is transmitted via droplets in the air that are inhaled, E. coli does not spread in the same way. It uses a rather longer route via fecal-oral transmission, where bacteria in faeces get onto hands and surfaces, or contaminate food and drink', says Corander.

Multi-drug resistant E. coli did not spread as fast

The two other variants of E. coli that the scientists investigated in the study, ST131-C1 and ST131-C2, are resistant to several classes of antibiotics and do therefore pose a bigger risk when causing infections. However, these two are not transmitted so easily between healthy individuals.

'This sounds like good news, but we detected some other challenges', says the professor.

The conclusion they came to was that the multi-drug resistant types of E. coli bacteria are more likely transmitted in hospitals and care homes where the frailest patients are. In these cases, an infection can pose a major threat to the survival, since several classes of antibiotics are no longer effective against these bacteria.

Multi-drug resistant E. coli probably survive better in hostile environments

Corander explains that the multi-drug resistant genotypes included in the study seem to have become very hardy and adept at survival. They likely defy the disinfectants frequently used in health care facilities and have obviously adapted themselves genetically so that they can survive in such settings.

'The conclusion that the multi-drug resistant E. coli variants are not transmitted so easily amongst healthy people, would suggest that these bacteria are also further assisted by medication to survive the continuously ongoing battle between different types of E. coli. The hypothesis is that since hospitalized patients are typically given antibiotics and other medicines, these kill off the competing more susceptible bacteria, helping the multi-drug resistant E. coli to become dominant', he explains.

Scientists want to find methods of killing bacteria without an excessive use of antibiotics

In the future, we risk not being able to treat infections caused by bacteria that have become resistant to critical antibiotics.

'So the next stage will be to find out why these variants of E. coli have developed such a capacity to survive under more selective pressure and the exact genetic reasons for their poorer transmissibility in the community settings. We also need fast and affordable ways for making rapid diagnosis and it will be important to find more ways of killing bacteria without resorting to use of broad-spectrum antibiotics. For example, in a number of new studies, researchers have tested the use of ultrasound on bacteria that hide behind biofilm - a thin layer of cellular material that they produce in order to protect themselves', says Corander.

Jukka Corander led the new study together with professor Pekka Marttinen from Aalto University in Finland.