title: Host and pathogen factors influencing urinary tract infections caused by Pseudomonas aeruginosa
Creators: name: Newman, John
Publisher: name: University of Liverpool Repository
Year: 2021

description: Urinary tract infections (UTIs) are one of the most common and costly infections in the world. UTIs can affect any part of the urinary tract: the urethra, bladder, ureters and, most seriously, the kidneys. UTIs can stay localized to the urinary tract or spread to the kidneys, abdomen and bloodstream. UTIs are most commonly seen in women and are typically caused by Escherichia coli. The pathogenesis of uropathogenic E. coli (UPEC) is a popular area of research and is increasingly well understood. Less commonly studied are other uropathogens such as P. aeruginosa. P. aeruginosa UTIs are more commonly seen in catheterized patients and the elderly, where both men and women are equally affected. P. aeruginosa UTIs in elderly patients are associated with high levels of morbidity and mortality. P. aeruginosa is an opportunistic Gram-negative pathogen that is frequently isolated in lung, eye and wound infections and is characterized by its large, adaptable genome and high levels of antibiotic resistance. Research into P. aeruginosa infections in the lungs of cystic fibrosis patients has found that P. aeruginosa can evolve into diverse lineages that make elimination with antibiotics extremely difficult. UPEC can usually be successfully treated with a course of antibiotics that relieve symptoms of UTI, but patients will often experience recurrence of UTI weeks or months later – sometimes with the same strain. UPEC researchers have attributed this to the ability of UPEC to invade the epithelium of the urinary tract where it can lie dormant in quiescent intracellular reservoirs protected from antibiotics and the immune system. The work aimed to investigate if phenotypic and genotypic diversity could occur in P. aeruginosa UTIs, determine if P. aeruginosa can invade epithelial cells of the urinary tract in a similar fashion to UPEC, and identify genes that help P. aeruginosa to act as an intracellular pathogen in the urinary tract. P. aeruginosa UTI samples were obtained from 5 elderly patients at the Royal Liverpool University Hospital. 40 isolates were taken from each patient sample and screened for phenotypic heterogeneity across measures of antibiotic resistance, hypermutability, auxotrophy and virulence factor production. Evidence of phenotypic heterogeneity was found and supported by genome sequencing of the most phenotypically diverse pairs of isolates from each of the 5 patient samples. Genotypic differences were found between pairs of isolates from 3/5 patients in the form of non-synonymous SNPs. There was no evidence for a single UTI patient being colonized by multiple strains of P. aeruginosa. Gentamicin protection assays and confocal microscopy provided novel evidence of P. aeruginosa’s ability to invade bladder epithelial cells in an in vitro model. This ability was conserved across lab strains PAO1 and PA14 as well as clinical UTI isolates. Finally, a transposon directed insertion site sequencing (TraDIS) experiment was performed to identify genes that may be required for successful invasion of bladder epithelial cells. Experimental issues plagued multiple repeats of the TraDIS experiment but the results that were salvaged highlighted genes that could likely prove important in P. aeruginosa UTI pathogenesis and offer targets for treatment. This work highlights the need for a better understanding of P. aeruginosa UTI pathogenesis so that better strategies can be adopted for the treatment of P. aeruginosa UTI.