Microbiology of Urinary Tract Infections

Bugs causing UTIs

Bug (Bacteria only)	Comments
E. coli	#1 leading cause of UTI
S. saprophyticus	#2 leading cause of UTI, common in young, sexually active women
K. pneumoniae
Proteus
P. aeruginosa	Common cause in patients with indwelling catheters
Serratia
Enterobacter cloacae
E. faecalis

Urinary tract infections
- cystitis (“bladder infection”)
  - dysuria
  - polyuria
  - suprapubic pain
  - WBCs in urine
    - no casts
  - systemic symptoms (e.g. fever) uncommon
- pyelonephritis (infection reaches upper urinary tract or kidney)
  - fever
  - chills
  - flank pain / costovertebral angle (CVA) tenderness
  - WBC casts in urine
  - hematuria
Diagnosis
- positive leukocyte esterase test = bacterial UTI
- positive Nitrite test = Gram-Negative bacterial UTI
Predisposing factors
- urinary catheterization
- diabetes
- pregnancy
- kidney surgery
- congenital defects
- vesicoureteral reflux (urine flows from bladder back to ureters)
- BPH
Epidemiology
- women affected 10x more frequently than men
  - shorter urethra
  - proximity of urethra to anus
  - colonization of vagina by fecal flora
- leading cause of UTIs is urinary catheters