Host-bacterial interactions underlying recurrent urinary tract infections

Abstract

Although most urinary tract infections (UTIs) are easily treated with antibiotics, many patients present with long-term bacterial colonisation of the urinary tract. Amongst these patients, some remain asymptomatic but others exhibit severe and frequent UTI symptoms. Currently, there is little understanding of the host-microbial interactions underpinning these clinical conditions. Hence further understanding of these interactions underlying the pathogenesis of asymptomatic bacteriuria (ASB) and recurrent UTIs is essential for effective clinical management. To explore these interactions further, genomic data from two clinical studies (AnTIC & BUTI) were mined and bacterial isolates exploited to determine the effects of antibiotic prophylaxis (AnTIC) and hostspecific factors (BUTI) on long-term bacterial colonisation. Using bioinformatic approaches, the AnTIC dataset was analysed to investigate the impact of antibiotic prophylaxis on bacterial colonisation of the urinary tract. The findings suggested that antibiotic prophylaxis reduced the frequency of symptomatic UTIs by not only clearing bacteria from the urinary tract, but also in a subset of patients through stabilising Escherichia coli colonisation. An association between stable colonisation and a reduction in UTI frequency was also observed in the BUTI study, but with a focus on Proteus mirabilis rather than E. coli. In these patients, host factors appeared important with patients characterised by a TLR1 1805T SNP associated with stable and clinically asymptomatic P. mirabilis colonisation. In vitro experiments using bladder RT4 cells and TLR agonists supported a role for TLR1 in modulating the immune response, which may play a role in ASB. Analysis of E. coli isolated from AnTIC patients supported a link between stable long-term bacterial colonisation and increased antibiotic resistance. In the UK, nitrofurantoin underpinned by the low incidence of resistance amongst uropathogens, is prescribed for managing UTIs. In vitro experiments using mutagenised clinical E. coli isolates were performed to investigate potential factors driving nitrofurantoin resistance. In the absence of nitrofurantoin, bacterial growth data demonstrated that nitrofurantoin resistant (NitR) strains grew as well as sensitive strains (NitS doubling time= 21.9 ± 0.9 min; NitR mutants= 25.7 ± 0.4 min; NitR natural= 25.7 ± 1.1 min). However, in the presence of nitrofurantoin (8 – 16 μg/ml), resistant strains showed a fitness advantage, with the average doubling time of these mutants reduced by 35% (p<0.001). These results in combination with clinical pharmacokinetics data suggest that urinary nitrofurantoin concentrations in prophylaxis therapy driving fitness via selective advantage, which potentially results in the selection of NitR isolates. Taken together, these studies show that investigating both host and microbial components and how they interact are essential to understanding the pathogenesis of UTI and will help improve the management of recurrent UTI sufferers.