Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Microbiology and Immunology

Supervisor

Reid, Gregor

2nd Supervisor

Burton, Jeremy P.

Co-Supervisor

Abstract

The purpose of this thesis was to increase understanding of enterococcal UTI, in particular, the response of Enterococcus to antibiotic prophylaxis in vitro and in vivo and enterococcal communication with the bladder.

We studied the in vitro effects of trimethoprim-sulfamethoxazole (TMP/SMX) and nitrofurantoin, two of the antibiotic treatments used most commonly in the management of both urinary tract infection (UTI) and recurrent UTI (RUTI), on Enterococcus faecalis attachment to urothelial cells. In doing so, we documented nitrofurantoin-induced increases in bacterial attachment at growth inhibitory concentrations of nitrofurantoin, but not TMP/SMX. This increased virulence did not correlate with increased expression of virulence factors but was correlated with increased expression of three putative genes.

We then explored whether this corresponded to alterations in bacterial communities throughout antibiotic prophylaxis for paediatric patients with RUTI. Our bacterial culture results indicated uropathogens were present in the urine of children with and without a history of RUTI and that antibiotic prophylaxis induced a transient decrease in uropathogen load. Interestingly, none of our patients were experiencing symptomatic UTI at the time of urine sample collection, yet a significant proportion of midstream urine samples met the clinical threshold for UTI, indicating these patients had asymptomatic bacteriuria (ABU). Further, E. faecalis bacterial load was positively correlated with non-E. coli uropathogens, suggesting some patients may be pre-disposed to polymicrobial UTI.

To elucidate mechanisms by which enterococci can mask the host’s perception of UTI, which may also contribute to the polymicrobial nature of E. faecalis UTI, we completed targeted metabolomics of neuroactive molecules in vitro under conditions mimicking the bladder environment. Our results suggest Enterococcus may produce tyramine in the bladder at concentrations that are likely to have a physiological effect on both urothelial cells and cohabiting bacteria.

Our data raises questions about the application of nitrofurantoin to enterococcal UTI and the efficacy of antibiotic prophylaxis for RUTI. Further, our clinical and in vitro data suggest E. faecalis may contribute more to polymicrobial UTI than previously thought. Indeed, enterococcal production of tyramine may explain the high incidence of enterococci in not only polymicrobial UTI but also other infections.

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