List bacterial pathogens.
Infection ascends from the urethra to the bladder.
Can ascend further to the ureters and the renal pelvises (see “Pyelonephritis”)
Escherichia coli: leading cause of UTI (approx. 80%) 
Staphylococcus saprophyticus: 2nd leading cause of UTI in sexually active women
Klebsiella pneumoniae: 3rd leading cause of UTI
Produces ammonia, giving the urine a pungent or irritating smell
Associated with struvite stone formation
Nosocomial bacteria: Serratia marcescens, Enterococci spp., and Pseudomonas aeruginosa are associated with increased drug resistance.
List viral and fungal pathogens.
Immunocompromised patients and children are particularly susceptible to viral UTIs. 
Adenovirus, cytomegalovirus, and BK virus are commonly involved in hemorrhagic cystitis. 
Yeast: rare (usually Candida species) 
Disseminated fungal infections (e.g., Blastomyces dermatitidis, Cryptococcus neoformans)
List host-dependent predisposing factors.
Structural or functional abnormalities of the urinary tract 
Prevent bladder emptying and/or result in urinary stasis
Benign prostatic hyperplasia
Congenital malformations causing vesicoureteral reflux
Urinary bladder diverticulum
Urinary tract calculi
Female individuals: anatomically predisposed because the urethra is shorter and anal and genital regions are in close proximity → bacteria spreading from the anal region → colonization of vagina → ascending UTIs 
Male individuals: higher risk in uncircumcised male infants 
Pregnancy: hormonal changes during pregnancy → urinary stasis and vesicoureteral reflux → increased risk of UTIs
Postmenopause: ↓ estrogen → ↓ vaginal lactobacilli → ↑ vaginal pH → ↑ colonization by E. coli 
Chronic constipation: common cause of UTIs in children
Previous UTI 
History of kidney surgery
Medication: recent use of antibiotics
List other factors.
Postcoital cystitis (honeymoon cystitis): a lower urinary tract infection that occurs in women after recent sexual activity, which can cause irritation of the urethral meatus and facilitate bacterial entry into the urethra (e.g., from the genital and/or anal region).
Diaphragm and spermicide use
Catheter-associated urinary tract infection (CAUTI)
Caused by indwelling urinary catheters
Most common cause of nosocomial urinary tract infection