2. URINARY TRACT INF.

Overview of Bacterial Urinary Tract Infections

Bacterial urinary tract infections (UTIs) represent a significant health concern, primarily affecting the bladder, urethra, and sometimes extending to the kidneys. Understanding the various causative agents, their mechanisms of action, diagnosis, and treatment is critical for effective management. This overview will delve into important classifications of bacteria, pathophysiology, clinical manifestations, specimen collection techniques, and laboratory processing of urine cultures.

Bacterial Classifications in UTIs

Aerobic and Facultative Anaerobes

Gram +

  • Cocci:

    • Staphylococci:

      • Coagulase positive: Staphylococcus aureus implicated in male prostatitis and epididymitis.

      • Coagulase negative: More common species include S. saprophyticus (rare) and S. epidermidis (contaminant)

    • Streptococci:

      • β-haemolytic:

        • S. agalactiae (frequently found in normal vaginal microbiota, in pregnant women: can cause neonatal meningitis - screening and antibiotic treatment)

        • S. pyogenes → related to prostatitis and epididymitis.

    • Enterococcus spp.: Includes E. faecalis and E. faecium.

Gram -

  • Bacilli:

    • Enterobacterales: Major pathogens include Escherichia coli, Klebsiella spp. (K. pneumoniae, K. oxytoca), and Proteus spp. (P. vulgaris, P. mirabilis).

    • Others: Include Pseudomonas aeruginosa and Stenotrophomonas maltophilia.

  • Cocci:

    • Neisseriacea: Acinetobacter spp.

Non-Cultivable and Fastidious Pathogens

  • Chlamydia trachomatis: Often considered in non-gonococcal urethritis.

  • Ureoplasma ureolyticum: Known for causing non-gonococcal urethritis (NGU).

  • Others: Neisseria gonorrhoeae and Mycobacterium spp. (e.g., Mycobacterium tuberculosis).

Pathophysiology of Urinary Tract Infections

Lower Urinary Tract Infections (LUTI)

  • Iatrogenic Causes: Catheterization is a significant risk factor leading to catheter-associated UTIs. Biofilm formation can occur on indwelling catheters, which causes further complications.

  • Anatomical Contamination: Bacteria from the skin microbiota, particularly around the urethra, can ascend and infect the urinary bladder.

  • Common Pathological Factors: Conditions such as nephrolithiasis (kidney stones), pregnancy, immunosuppression, diabetes mellitus, and neurogenic bladder issues contribute to susceptibility to infections.

Upper Urinary Tract Infections (UUTI)

  • Symptoms include fever and flank pain, and infections usually ascend from the bladder to the kidneys.

  • Iatrogenic origins such as ureteral catheter insertion can also play a role in these infections.

  • No urinary tract infection without proof of pyuria

    • Pyuria: the production of urine which contains white blood cells by automated urine analyser (>10/mm3) OR ≥ WBC per field of view at 400x magnification in centrifuged urine

Basic concepts of UTIs

Uncomplicated UTI

  1. Immunocompetent patient

  2. No comorbidities

  3. Non pregnant women

  4. Premenopausal age

  5. Non-recurring UTI in women

Complicated UTI

  1. UTI in men → as they have a low chance for getting a UTI normally

  2. Pregnancy

  3. Presence of a bladder catheter or other foreign body in the urinary tract, e.g. kidney stone

  4. Recent urological interventions

  5. Anatomical or functional disorders of the urinary tract (obstructions)

  6. Immunocompromised contions

→ group and dose of the recommended antibiotics differ for the two types of infection!! (EUCAST)

Sterile pyuria

  • the presence of elevated numbers of white cells in a urine which appears sterile using standard culture techniques (so no bacterial growth on medium)

  • causes of sterile pyuria:

    • treated UTI within 1-2 weeks of treatment

    • inadequately treated UTI

    • urethritis caused by fastidiously cultured bacteria

      • ureoplasma ureolyticum NGU = Non-gonorrhoeal urethritis, causing agent of nephrolyt = renal stone

    • Chlamydia trachomatis infection - NGU

    • Neisseria gonorrhoea - gonorrhoea, STD

    • Genitourinary tuberculosis

    • renal stones

    • prostatitis

    • tubulo-interstitial nephritis

    • renal papillary necrosis (e.g. from analgesic excess)

    • urinary tract neoplasm

Signs and Symptoms of UTIs

  • Lower UTI Symptoms: Characterized by dysuria (painful urination), frequent and urgent urination, and potential complications such as prostatitis in men.

  • Upper UTI Symptoms: Manifestations of pyelonephritis include systemic symptoms like fever and localized flank pain.

Diagnostic Methods

Specimen Collection

  • Clean-Catch Midstream Urine Samples: Essential for obtaining a reliable urine specimen; steps must be followed to minimize contamination.

  • Child and Adult Collection Techniques: Guidelines to ensure no contamination from genital flora are important; techniques differ slightly between males and females.

  • Urine Culture Techniques: Utilize sterile containers and transport samples promptly to laboratories for accurate culture and sensitivity analysis.

Microbiological Processing

  • Specimens are cultured on selective media (e.g., blood agar, eosin methylene blue agar), incubated to allow bacterial growth, followed by evaluation and antibiotic susceptibility testing.

Interpretation of Urine Culture Results

  • The threshold for significant bacteriuria is defined as 105 cfu/ml. Lower counts suggest contamination or possible false positivity, whereas counts greater than this indicate a likely infection requiring appropriate therapy based on identified pathogens.

  • Considerations during interpretation include patient history and clinical symptoms to tailor treatments effectively. Care must be taken to avoid misinterpretation of results, especially in atypical presentations and populations.

Conclusion

Bacterial urinary tract infections predominantly involve a variety of microorganisms, with patient-specific factors influencing their occurrence and management. Understanding the classification, pathophysiology, and diagnostic approaches is pivotal for effective intervention and treatment strategies.