Microbiology of the urinary tract

Question 1

Symptoms of UTI

Answer 1

1. Polyuria
2. Dysuria
3. Urgency
4. Fever
5. Suprapubic discomfort
6. Haematuria

Question 2

Symptoms of pyelonephritis

Answer 2

1. Symptoms of cystitis (bladder infection)
2. Loin pain
3. Fever
4. Rigors
5. Renal angle tenderness

Question 3

Explain how catheters cause UTIs and how this can be prevented

Answer 3

• They bypass the defence mechanism of the urinary tract and act as a foreign body.
• Bacteria form biofilm on the catheters
• 5-10% increase in prevalence of bacteriuria each day a catheter remains in situ
• All catheters eventually get colonised
• Catheter-associated bacteriuria does not require antimicrobials, only if the patient has signs/symptoms of infection

Prevention:

1. Not catheterising the patient
2. Limited duration of catheter
3. Aseptic insertion
4. Closed drainage system

Question 4

UTI causing bacteria, community vs hospital acquired & OTHER

Answer 4

Community:

• E.coli (UPEC)
• Coagulase-negative staphylococci
• Staph. epidermidis
• Staph. aureus
• E.terococcus faecalis

Hospital:

• Candida
• Proteus
• Klebsiella
• Enterobacter
• Serratia
• Pseudonomas aeruginosa

OTHER:

• Adenoviruses
• BK and JC viruses
• TB
• Schistosoma haematobium

Question 5

Host defences against UTI

Answer 5

1. Urine flow and micturition
2. Urine - osmolality, pH, organic acids (anti-microbial agent)
3. Secreted factors - sIgA (sticks to bacteria), lactoferrin (iron chelator)
4. Mucosal defences - Mucopolysaccharides (slows down bacteria), few receptors (bacteria can’t invade cells)

Question 6

Virulence factors of UPEC & which strains are each factor associated with

Answer 6

1. Type 1 fimbriae
   - Associated with cystitis-causing strains
   - Hairs that stick to bladder epithelium. Bind to mannose residues on bladder endothelial cells membrane
2. Type P fimbriae
   - Associated with pyelonephritis-causing strains
   - Bind to glycolipid residues on host cells
3. Bacterial capsule
   - Associated with cystitis-causing strains
   - K antigen. Resists phagocytosis

Question 7

Proteus species virulence factors

Answer 7

• G-ve bacteria
• Proteus mirabilis is the most common
• Produces urease. Increases pH of urine. Production of magnesium ammonium (struvite) stones, surrounds and protects the proteus

Question 8

Diagnostic criteria for UTIs & pros/cons

Answer 8

1. UTI signs in urine
   - Cloudy urine
   - Urine dipstick
2. Urinalysis
   - Protein
   - Blood
   - Leukocyte esterase* (esterase produced by leukocytes, sign of WBCs in urine)
   - Nitrites* (bacteria have enzyme nitrate reductase that converts nitrates into nitrites)

Pros = high NPV (rule out) but lower PPV (ruling in)

Cons = nitrite may be falsely negative (such as taking vit C). Leukocyte esterase may be falsely negative (patient taking antibiotics or high glucose in urine)

Question 9

Management of uncomplicated lower UTI

Answer 9

1. Maintain good hydration
2. May resolve spontaneously
3. May use microbials in order (trimethoprim, nitrofurantoin, ampicillin/amoxicillin, ciprofloxacin)

Question 10

Management of recurrent UTI

Answer 10

1. Antibiotics
2. Self-medication - cranberry juice tablets (contain proanthocyanidins)
3. Voiding post-intercourse & HRT in post-menopausal women

Question 11

UTI treatment in children (lower tract, upper tract mild & severe)

Answer 11

Lower tract: amoxicillin, trimethoprim, cephalexin

Upper tract mild: co-amoxiclav

Upper tract severe: Cefotaxime, gentamicin