Abstract:
Urinary tract infections (UTIs) are considered to be the most commonly encountered bacterial infection in humans, with uropathogenic Escherichia coli (UPEC) identified as the predominant causative agent. The ability of UPEC to form intracellular bacterial communities (IBCs) in bladder epithelial cells promotes survival of the pathogen in the host and acts as a bacterial reservoir for recurrent infection. UPEC 536 forms biofilm-like aggregates in response to an iron-restricted environment, such as is encountered in the urinary tract, which disperse upon the provision of iron. Dysregulation of the aggregation and dispersal cycle was hypothesised to affect virulence in a Galleria mellonella larvae assay. In vitro, a ΔbcsA mutant fails to form biofilm-like aggregates and aggregate dispersal is dependent on the expression of yhjK. In vivo, results suggested that the ΔbcsA mutant is marginally more virulent and a ΔyhjK mutant is slightly less virulent when survival rates, caterpillar health and LD50 are compared to parent UPEC 536. A recurrent infection model was piloted exploiting the advantages of bioluminescence and, in conjunction with Gram’s stain visualisation of larval haemolymph, it was proposed that the formation of biofilm-like aggregates in vivo may be associated with the pathogenesis of UPEC 536ΔyhjK. qPCR analysis produced the novel finding that yhjK is expressed as part of the cellulose biosynthesis operon, bcsABZC. Relative gene expression within the operon during aggregate formation in iron-restricted conditions was compared to expression during iron-induced dispersal; results suggest that an increase in cellulose production is not due to an upregulation in gene expression, and it was proposed that activation of cellulose biosynthesis may occur on a post-transcriptional level.