Bacteria lurking in everyday store-bought meat may be causing thousands of urinary tract infections, especially in lower-income communities.
Study: Zoonotic Escherichia coli and urinary tract infections in Southern California. Image credit: Sergey Ryzhov/Shutterstock.com
*Important notice: mBio publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
Urinary tract infections (UTIs) are prevalent worldwide and mainly caused by Escherichia coli (E. coli). In some cases, this bacterium may be acquired through consuming meat from infected animals, the zoonotic route. A recent study published in Clinical Microbiology examines the proportion of metropolitan-area UTIs caused by zoonotic extraintestinal pathogenic E. coli (ExPEC) in Southern California.
Introduction
E. coli colonizes humans and animals, including those domesticated for meat. Infections caused by this bacterium cause an estimated one million deaths globally each year.
ExPEC strains cause infections beyond the gut, including UTIs, cystitis, pyelonephritis, sepsis, and meningitis. About eight million UTIs occur each year in the United States alone. They significantly affect productivity and the cost of healthcare. Many become severe infections, with UTIs responsible for over half of sepsis due to E. coli.
Food animals may be responsible for a notable minority of these bacterial infections, more than previously thought. However, the contribution of zoonotic ExPEC to the burden of infection remains unclear, mainly because these infections are typically sporadic and because over nine billion animals are raised for meat in the USA. Given that E. coli is a common bacterium in both human and animal populations, it is challenging to distinguish sporadic from endemic strains.
The gold standard method is core-genome phylogenetic analysis, commonly used to pinpoint the origin of an infectious outbreak. However, it requires a large representative sample of the suspected population. Even without this, however, it can be used to identify the primary host species.
The current study used a Bayesian latent class genomic attribution model on a large set of E. coli isolates. This statistical-genomic method combines core-genome phylogeny with mobile genetic elements (MGEs) that show distinguishable differences between food animals and humans. This method assessed the percentage of zoonotic strains contributing to the total UTI burden in Southern California. The aim was to gain actionable insights into the risk of infection with these strains.
About the study
The study involved eight Southern California counties and lasted from 2017 to 2021. The researchers obtained 12,616 isolates of E. coli from retail meat and 23,483 from patients with UTI, looking to compare them with a representative sample of 5,728 isolates.
Study findings
The study participants mostly included women, with a median age of 50. About 37% were Hispanic, and 31% were White.
E. coli contamination was highest in turkey (82%) and ranged between 47% and 58% for beef, chicken, and pork in the sampled retail meats. The most contaminated samples were from poor neighborhoods, with 12% higher contamination rates for every 10% absolute increase in family poverty rate for that region. Value packs were also more likely to be contaminated.
This pattern may reflect improper meat handling, inadequate storage temperatures, or extended storage periods. Socioeconomic conditions and access to food safety resources could influence contamination and infection risk.
Older men were more likely to have zoonotic infections, the median age being 73, compared to 65 for those with non-zoonotic infections. Zoonotic ExPEC strains were more frequent in women than men, at 20% vs. 8.5%, respectively.
Unique sequence types were useful in distinguishing isolates by their origin. Sequence types from clinical isolates were different from those that dominated meat isolates. Their distribution pattern also distinguished zoonotic from non-zoonotic ExPEC strains.
MGEs also showed enrichment patterns that were different in human isolates than in meat. Chicken and turkey meat isolates had elements like M1, M2, M4, and M5 at high frequency. Conversely, human-associated elements such as H2, H3, and H6 were more likely in isolates from UTIs.
Overall, nearly one in five (18%) UTIs were linked to ExPEC strains derived from food animals. The proportion rose to 21.5% in poor neighborhoods, a 1.6-fold higher risk than in low-poverty areas.
A large proportion of ExPEC strains found in clinical UTI samples were linked to a few E. coli strains in the B2 and D phylogroups isolated from meat, suggesting these particularly virulent strains play a key role in zoonotic UTI risk, probably due to their virulence. The findings that the prevalence of these strains in zoonotic UTIs did not directly mirror their abundance in meat samples support this. Poultry meat, especially turkey, appears to be the highest-risk among all animal foods for virulent ExPEC-linked infection.
Zoonotic strains showed intermediate antimicrobial resistance genes between the clinical and meat-derived isolates. They were less likely to show multidrug resistance than non-zoonotic isolates, but not different from meat isolates. Both zoonotic and meat isolates were less resistant to commonly used antimicrobials, except for tetracyclines.
However, zoonotic and non-zoonotic clinical strains were less likely to show gentamicin resistance than meat isolates. This may reflect regulatory and agricultural changes, such as reduced antimicrobial use in livestock under policies like California Senate Bill 27, that have lowered resistance among bacteria linked to zoonotic UTIs.
Conclusions
These findings underscore the contribution of zoonotic ExPEC to the UTI burden in Southern California and the need for targeted interventions to reduce risk in vulnerable communities.
With nearly a fifth of UTIs in this population being linked to zoonotic ExPEC strains, this study indicates the urgency of framing food safety interventions to reduce the prevalence of these strains in the food supply, especially poultry meat.
The authors also note limitations: the model could not distinguish all meat sources, particularly cattle, and the study focused mainly on outpatient community-acquired infections, which may underestimate the full zoonotic contribution.
More work is required to establish the clinical value of reducing the use of clinically relevant antimicrobials in food animals, potentially reducing antimicrobial resistance in human infections. Meanwhile, high-risk groups like immunocompromised and older adults should be careful when dealing with any form of raw meat, paying attention to hand hygiene and avoiding cross-contamination, while ensuring thorough meat cooking before consumption.
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*Important notice: mBio publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
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