Mechanisms of pain from urinary tract infection

The pain response to urinary tract infection is largely uncharacterized, but the symptomatic response to urinary tract infection contrasts with the lack of pain response among individuals with asymptomatic bacteriuria. Quantifying pelvic pain in a murine urinary tract infection model, uropathogenic Escerichia coli induces transient pelvic pain, whereas an asymptomatic bacteriuria E. coli isolate causes no pain, thus recapitulating the spectrum of clinical responses to intravesical E. coli. These differential pain responses are not correlated with bladder colonization or inflammation, but instead are intrinsic to E. coli lipopolysaccharide and dependent on the lipopolysaccharide receptor, TLR4. Epidemiological data suggest a link between interstitial cystitis and a history of urinary tract infection, so it was evaluated whether repetitive uropathogenic E. coli instillation would result in chronic pain through central sensitization. Although repeated infection with wild type uropathogenic E. coli results in only transient episodes of acute pain, a uropathogenic E. coli mutant lacking O-antigen causes chronic, post-urinary tract infection pelvic pain. Similarly, a K-12 E. coli strain lacking O-antigen induces chronic pain that persisted long after bacterial clearance, and expressing O-antigen nullified the pain phenotype. Spinal cords isolated from mice with post-urinary tract infection chronic pain showed deficits in short-term depression consistent with central sensitization. Deleting O-antigen gene complex from a uropathogenic E. coli strain and subsequent heterologous expression of O-antigen gene clusters shows that a single bacterial isolate can exhibit pain phenotypes ranging from a null phenotype, an acute pain phenotype, to a chronic pain phenotype. Post-urinary tract infection chronic pain is also associated with voiding dysfunction and anxious/depressive behavior. These effects are also mediated by TRPV1 at the level of pain establishment and CCR2 at the level of pain maintenance. Together, these findings show that transient infection with E. coli might result in chronic visceral pain with the hallmarks of neuropathic pain. This pattern of behaviors mimics the spectrum of interstitial cystitis symptoms, thus supporting the possibility of an infectious etiology of interstitial cystitis.