(A) Bystander: gut does not affect susceptibility to rUTI. Other mechanisms prevent either UPEC colonization of the gut or invasion of the bladder in healthy women. (B) Facilitator: dysbiotic gut facilitates UPEC colonization in rUTI. More abundant and/or more urovirulent E. coli (darker shade of red) in the guts of rUTI women increase the risk of bladder infection. (C) Agitator: UPEC invasion of the bladder occurs in all women, but interactions between a dysbiotic gut and the host immune system result in increased inflammation and symptom severity in rUTI women. The bottom panel illustrates some of the many states of the gut-bladder axis in otherwise healthy people. Hair-like fibers are type 1 pili. GI, gastrointestinal.