Countering long-held theories on how urinary tract infections (UTIs) are spread, a new study has found that a strain of E. coli known to cause a large proportion of bacterial UTIs may be passing to new hosts through contaminated store-bought poultry products.
"In the past, we could say that E. coli from people and poultry were related to one another, but with this study, we can more confidently say that the E. coli went from poultry to people and not vice versa," lead researcher Lance B. Price said in a statement.
Writing in the open-access journal mBio, Price and his colleagues explain that a widely distributed E. coli subtype called E. coli ST131 has evolved the ability to rapidly colonize the human bladder after it enters the bloodstream. In the early 2000s, the strain exploded in prevalence and subsequently acquired resistance to multiple antibiotic agents. E. coli ST131 is now the most troubling UTI pathogen in circulation. If left untreated, or if the patient has a compromised immune system, the infection may progress to the kidneys and become life-threatening.
Epidemiologists speculate that the most common ST131 lineage, ST131-H30, spreads from person-to-person from community and hospital exposure, given that previous studies found that food animals are not a significant reservoir. However, little work had been done on the transmission of a different lineage, ST131-H22. This strain interested Price and his team because it is often found inside living chickens and turkeys and the meat products made from them. It also carries the mobile gene elements that confer resistance to colistin, a drug reserved as a last resort agent against several human pathogens.
To assess whether patients could be contracting ST131-H22 UTIs through food, they spent one year collecting and analyzing 1,725 blood and urine samples from all UTI cases diagnosed in Flagstaff, Arizona, and analyzed 2,452 samples of retail meat from all available brands, purchased twice a month from every major grocery chain in the area. About 72 percent of all human samples tested positive for some strain of E.coli, as did nearly 80 percent of those from meat. Twenty-five meat isolates (of which 24 were from poultry) and 24 human clinical isolates were determined to be ST131-H22 specifically.
Using advanced genetic analysis techniques, the team then compared the genomes of the ST131-H22 bacteria cultured from each source. The results indicated that the human isolates were nearly identical to those from poultry products, and that nearly all ST131-H22 bacteria carried a particular DNA element that is known to give human-adapted E. coli strains the ability to thrive in birds. Comparisons to DNA from ST131-H22 lineages from elsewhere in the world suggest that this pathogen has evolved the ability to jump from humans to birds – and back again – at least six times since the 1940s.
"This particular E. coli strain appears capable of thriving in poultry and causing disease in people," first author Dr Cindy Liu added. "Poultry products could be an important vehicle for bacteria that can cause diseases other than diarrhea."
According to Price, E. coli products are currently not routinely tested for the E. coli strains that may cause UTIs. His work, sponsored in part by the National Institutes of Health, could help change that.
"We are now working to measure what proportion of UTIs might be caused by foodborne E. coli by looking at all E. coli strains, not only ST131," Price said. "This is not an easy question to answer but an extremely important one."