Urinary tract infections (UTIs) are fairly common, with at least 50% of women experiencing a UTI once during her life. Many UTIs respond well to antibiotics when diagnosed and treated, but without treatment, an infection can spread to the kidneys and even become systemic. The unfortunate rise in drug-resistant infections means that some UTIs don’t respond to antibiotic therapy, which also puts patients at risk for disseminated infection.
UTIs are a major problem both for those in hospitals for unrelated treatment and for those who are otherwise healthy in the community. Drug-resistant UTIs are increasing both in hospital-acquired and community-acquired infections, highlighted this last week in a list from the World Health Organization of the major drug-resistant bacterial groups. This list noted that carbapenem-resistant Enterobacteriaceae (CRE), which include common UTI infectious agents Escherichia coli, Klebsiella pneumoniae, and Proteus species, are among the drug-resistant bacteria for which new therapies are most critical.
We've discussed the hard work clinical microbiologists are doing to systematically find the best sample collection method for accurate UTI diagnoses, as well as the work toward predicting UTI antibiotic resistance profiles based on patient history. Today comes a new Applied and Environmental Microbiology study addressing another important aspect of UTIs: the association of foodborne resistant bacteria and resistant UTIs.
Applied and Environmental Microbiology: Extraintestinal Pathogenic and Antimicrobial-Resistant Escherichia coli, including Sequence Type 131 (ST131), from Retail Chicken Breasts in the United States in 2013
The study follows a long line of research linking chicken meat products to the spread of drug-resistant E. coli strains capable of causing disease. Genetic similarities between extraintestinal pathogenic E. coli (ExPEC) and retail meat products have shifted the understanding within the biomedical community of UTI transmission and infection.
The AEM study looked at carriage of E. coli by chicken products, mostly chicken breasts, from across the United States Source.
The new AEM study examined chicken products collected in 2013. 205 (65%) of 316 samples tested were culture-positive for E. coli, and 25 were ExPEC. The researchers tested cultured bacteria by amplifying ExPEC-specific genetic markers; samples were considered ExPEC-positive if they contained two of the five markers tested. Once identified, the research team, led by first author James Johnson and senior scientist Urvashi Rangan, looked for additional virulence-associated genes and determined the sequence type and antimicrobial susceptibility for each isolate.
Over half the ExPEC strains were resistant to at least one antibiotic class, and 33% of the strains were resistant to multiple antibiotics, with resistance most commonly found against antibiotic classes frequently used in poultry production. Resistance levels were lower from products marked “organic” or “no antibiotics,” although the virulence characteristics didn’t vary among the product types. This means ExPEC strains are equally able to cause disease regardless of the source, but are more likely to respond to antibiotic therapy if consumed from products that explicitly ban antibiotics in animal practices.
The phylogenetic groups, or phylogroups, of ExPEC observed were very similar to those seen in human patients. Most ExPEC clinical isolates, including the Sequence Type 131 (ST131) pandemic lineage, are in the B2 phylogroup. In the AEM study, 11 of the 25 chicken ExPEC isolates were in the B2 phylogroup, including 5 ST131 isolates. Because the samples were taken from throughout the United States, this demonstrates the ubiquity of contaminating, clinically related ExPEC strains among chicken products.
This study doesn’t directly connect the contaminated chicken to UTIs, but adds to the evidence that clinically relevant strains are associated with meat products. 70-95% of UTIs are caused by E. coli, including ST131, and the genetic similarities between the chicken and clinical isolates are supportive, but not causative; it will be important to consider the routes of transmission in follow-up studies using technologies like whole-genome sequencing that can determine strain relatedness down to the nucleotide level. Even if a direct link is made, it’s highly unlikely that all UTIs are caused by contaminated meats. However, the wide distribution of clinically relevant isolates, and the wide variety of multidrug resistant isolates, is cause for concern.
Urinary Tract Infections: Molecular Pathogenesis and Clinical Management. Now available at ASM Press.
Because antibiotic resistance genes were common among the chicken isolates, there is the double threat that infections will become more difficult to treat and that the resistance genes can easily be passed other pathogenic microbes. Some scientists argue that the antibiotics fed to livestock lead to resistant strains that can seed infection in people. There is some support for this: the recent mcr-1 colistin-resistant E. coli infection in the United States was found in a woman suffering a UTI, and chicken products have been found to harbor mcr-1. Future studies will determine whether there is a strong association between these two phenomena.
The newly published book Urinary Tract Infections: Molecular Pathogenesis and Clinical Management, Second Edition covers issues such as source of infection in much greater detail. The text covers the clinical aspects, virulence mechanisms, and host responses to UTIs, with each section authored by subject-matter experts.