109. Microbiological Aspects of Urinary Tract Infections (UTIs)

Covers urinary tract infections from definition through to prevention, following the order of classification, causative organisms, pathogenesis, clinical forms, diagnosis and treatment. Tables set out the UTI types, the main pathogens with their notes, and the clinical features of each form, and a short section outlines antibiotic choices for uncomplicated, complicated, pyelonephritis and catheter-related infections. It closes with prevention measures, including prophylaxis in recurrent cases.

Inside: 9 sections · 1 labelled picture · 6 tables · 15 flashcards · 3 min

Topic 109 of 113 in the MU Sofia syllabus for Microbiology (Medicine, Year 3). The free AceMed note covers it in 9 sections, about 200 words (3 min of reading), with 15 flashcards.

I. Definition and Overview

UTIs are infections involving any part of the urinary tract: urethra, bladder, ureters, or kidneys.
Most are caused by ascending infection of bacteria from the urethra.
Common in females due to shorter urethra and proximity to anus.

IV. Pathogenesis

1. Colonization of periurethral area → often from gut flora
2. Ascending infection into bladder (cystitis), then kidneys (pyelonephritis)
3. Virulence factors:

E. coli: adhesins (P pili, type 1 fimbriae), hemolysin, siderophores
Proteus: urease alters urine pH
Biofilm formation in catheterized patients

VI. Diagnosis

A. Specimen Collection

Midstream clean-catch urine (preferred)
Catheter aspirate
Avoid swabs

B. Tests

UTI Treatment

Uncomplicated UTIs are treated with nitrofurantoin (5 days), TMP-SMX (3 days), or fosfomycin (single dose). Fluoroquinolones are reserved due to resistance concerns.

Complicated UTIs need broad-spectrum antibiotics like ciprofloxacin or ceftriaxone for 7–14 days, depending on severity. Always address underlying causes like catheters or obstruction.

Pyelonephritis (kidney infection) starts with IV ceftriaxone or ciprofloxacin, then switches to oral antibiotics for 10–14 days total.

Catheter-related UTIs require catheter removal/change and antibiotics targeting resistant organisms (e.g., ciprofloxacin, piperacillin-tazobactam).

Asymptomatic bacteriuria is only treated in pregnancy and before urologic procedures