Harmless or deadly? New study examines evolution of E. coli bacteria

E. coli usually live as harmless bacteria in the gastrointestinal tracts of birds and mammals, including humans. They also reside, independent of a host, in environments such as water and soil, and in food products including chicken and turkey meat, raw milk, beef, pork and mixed salad.

These bacteria can cause disease if they possess or acquire factors that allow them survive in areas of the human body outside the gut.

E. coli is the primary source of urinary tract infections, a common reason for hospital admissions. It can also lead to sepsis, which kills 11 million people globally each year, and meningitis, an infection that affects the brain and spinal cord.

Dr Cameron Reid, from the University of Technology Sydney, said the aim of the study, recently published in Nature Communications, was to better understand the evolution and genomic characteristics of an emerging strain of E. coli known as ST58.

ST58 has been isolated from bloodstream infections in patients around the world, including France, where the number of infections with this strain was shown to have doubled over a 12 year period. ST58 is also more drug resistant than other strains.

"Our team analysed E. coli ST58 genomes from more than 700 human, animal and environmental sources around the world, to look for clues as to why it is an emerging cause of sepsis and urinary tract infections," said Dr Reid.

"We found that E. coli ST58 from pigs, cattle and chickens contain pieces of genetic material, called ColV plasmids, which are characteristic of this strain of disease causing E. coli," he said.

Plasmids are tiny double-stranded DNA molecules, separate from the bacterial chromosome, that can replicate independently and transfer across different E. coli strains, aiding the evolution of virulence.

Acquisition of ColV plasmids may prime E. coli strains to cause extra-intestinal infections in humans, and also increase the likelihood of antimicrobial resistance, the research suggests.

"Zoonosis, particularly in relation to E. coli, should not be viewed simply as the transfer of a pathogen from an animal to a human," said research co-author Professor Steven Djordjevic.

"Rather, it should be understood as a complex phenomenon arising from a vast network of interactions between groups of E. coli (and other bacteria), and the selective pressures they encounter in both humans and animals," he said.

The findings suggest all three major sectors of food animal production (cattle, chickens and pigs), have acted as backgrounds for the evolution and emergence of this pathogen.

"The contribution of non-human sources to infectious disease in humans is typically poorly understood and its potential importance under-appreciated, as the debate regarding the ecological origins of the SARS-CoV2 virus attest," said Dr Reid.

"In a globalised world, eminently susceptible to rapid dissemination of pathogens, the importance of pro-active management of microbial threats to public health cannot be understated."

The study has broad implications for public health policy that spans across food industry, veterinary and clinical settings.

"To date, infectious disease public health has been a reactive discipline, where action can only be taken after a pathogen has emerged and done some damage," said Dr Reid.

"Ideally, with the advent and widespread uptake of genome sequencing technology, future infectious disease public health can transition to a primarily pro-active discipline, where genomic surveillance systems are able to predict pathogen emergence and inform effective interventions."

Dr Reid said for such a system to work, it requires ongoing research and collaboration with government, public health bodies, food producers and clinicians, and it would involve surveillance of a variety of non-human sources of microbes.

"This would include domestic and wild animals -- particularly birds -- food products, sewerage and waterways, in what is referred to as a 'One Health' approach. Some microbes, like ST58 E. coli, know very few barriers between these increasingly interconnected hosts and environments.

"A One Health genomic pathogen surveillance system would be a revolution within public health and do much to break down historically human-centric approaches devoid of connection with the world around us."