Urinary tract infections (UTIs) are the second most common bacterial infection with high recurrence rates. A major causative agent of UTIs are uropathogenic Escherichia coli (UPEC), which employ multiple mechanisms to invade and persist in host cells. With the rise of multi-drug resistant (MDR) UPEC, UTI treatment is becoming increasingly difficult and costly.
Here we used a mouse model of MDR UTI to investigate adaptive immune responses and their contribution to controlling infection. C57BL/6J wild-type or rag1-/-mice were transurethrally inoculated with an MDR strain of UPEC ST131 (EC958). Infection outcomes were assessed via flow cytometry and bacterial quantification of bladders and urine. In bladder-draining lymph nodes, germinal centre (GC) B cell responses had developed by 4 weeks post-infection and tapered off at 7 weeks post-infection. At 4 weeks, rag1-/-mice had significantly higher loads of bacteria in their bladders compared to wild-type mice, suggesting a role for adaptive immune responses in protecting against UTI. At 7 weeks post inoculation, detectable bladder bacteria remained in the majority of infected wild-type mice, which speaks to the many mechanisms of persistence that UPEC employ to evade the immune response.
One such mechanism is the formation of UPEC intracellular bacterial communities (IBCs). As IBCs are biofilm-like structures that could potentially be reservoirs for recurrent infections, this study also investigates if IBCs can be targeted using nitroxide functionalised antibiotics. We first showed that nitroxide-ciprofloxacin hybrids can successfully eradicate UPEC biofilms in vitro by simultaneously signalling cell dispersal and killing. Pilot studies in a mouse UTI model involving IBC formation at early infection stages, showed that a short 1-hour ex vivo bladder treatment with a nitroxide functionalised antibiotic resulted in decreased intracellular bacterial compared to the gentamicin-only treated group. These preliminary results show promise for these compounds as potential UTI therapeutics. Investigations are currently ongoing into their mode of action against UPEC, and their activity in mouse UTI treatment regimes ex vivo and in vivo.