Microbiology of the Urinary Tract Flashcards
What are the main routes of UTI acquisition?
Ascending (from urethra to bladder/kidney) and haematogenous (from blood to kidney).
What are the main sites of UTI?
Urethra (urethritis), bladder (cystitis), kidney (pyelonephritis).
What’s the difference between community-acquired and nosocomial UTI?
Community-acquired occurs outside healthcare settings; nosocomial occurs during hospitalisation, often catheter-related.
How common are UTIs in women?
5% of women present to GPs annually; up to 50% experience one in their lifetime.
What is the most common cause of UTI?
Uropathogenic E. coli (UPEC), a normal flora of the large bowel.
Name other infectious causes of UTI besides E. coli.
Adenoviruses, BK/JC viruses (post-transplant), Mycobacterium tuberculosis, Schistosoma haematobium.
Name 4 host defences against UTI.
- Urine flow/micturition
- Urine chemistry (pH, osmolality)
- Secreted factors: sIgA, lactoferrin
- Mucosal defences: mucopolysaccharides, low receptor density
What are Type 1 fimbriae?
E. coli structures that bind to mannose residues, associated with cystitis (lower UTI).
What are Type P fimbriae and K antigens?
Type P fimbriae bind to kidney cells; K antigen inhibits phagocytosis—both linked to pyelonephritis.
What are risks of UTI during pregnancy?
Low birth weight, premature delivery, perinatal morbidity, pyelonephritis (30% of untreated cases).
Symptoms of cystitis in pregnancy?
Frequency, urgency, dysuria, suprapubic discomfort, mild/no fever.
Symptoms of pyelonephritis?
Cystitis symptoms + loin pain, fever, rigors, renal angle tenderness.
What does urinalysis detect in UTI?
Protein, blood, leukocyte esterase, nitrites.
What can cause false negatives in urinalysis?
Antibiotics, low bacteria count, high glucose, non-nitrate-reducing bacteria.
What suggests contamination in urine microscopy?
Presence of epithelial cells.
What is the most common nosocomial infection?
Catheter-associated UTI.
How do catheters increase UTI risk?
Bypass defences, act as foreign bodies, allow biofilm formation.
Catheter-associated UTI: What works to prevent it?
Aseptic insertion, limiting duration, closed drainage, silver-bonded catheters.
What does NOT help prevent catheter-associated UTI?
Soap at meatus, bladder irrigation with antiseptics.
What is urethral syndrome?
UTI symptoms with negative cultures, often due to fastidious organisms or non-infectious causes.
First-line management of uncomplicated lower UTI?
Hydration; may resolve spontaneously. If antibiotics needed: short 3-day course.
Why use short antibiotic courses for UTI?
Reduce resistance, fewer side effects, as effective as longer courses.
When is antimicrobial prophylaxis considered in women?
If >3 UTIs annually.
When should a urine sample be sent in children?
If fever >38°C for >24 hours.
What are UTI risk factors in children?
Poor flow, recurrent fever, renal abnormalities, VUR, constipation, poor growth, high BP, etc.
How is UTI diagnosed in children <3 months?
Less reliance on dipsticks; follow NICE CG160 guidance.
Antibiotics for lower tract UTI in children?
Amoxicillin, trimethoprim, cephalexin.
Antibiotics for upper tract UTI (mild)?
Co-amoxiclav.
Antibiotics for upper tract UTI (severe)?
Cefotaxime or gentamicin.
Why is E. coli the most common cause of UTI?
It’s part of normal bowel flora and has specific virulence factors that promote UTI.
When should catheter-associated bacteriuria be treated?
Only if symptomatic.
What does a high number of white cells in urine microscopy suggest?
Infection (presence of pyuria).
What does a high number of epithelial cells in urine suggest?
Contamination of the urine sample.
What are causes of red blood cells in urine?
Menstruation, infection, stones, tumours.
Why does nitrite have low sensitivity in urinalysis?
Not all bacteria reduce nitrate to nitrite; low bacterial count may also cause false negatives.
What does leukocyte esterase detect?
Presence of neutrophils (indirect evidence of infection).
How fast does bacteriuria develop in catheterised patients?
Increases by 5–10% for each day the catheter remains in place.
Should asymptomatic catheter-associated bacteriuria be treated?
No, only if patient is symptomatic.
What is a key method to reduce CAUTI?
Avoid unnecessary catheterisation and remove promptly.
What percentage of women with cystitis symptoms have negative cultures?
Up to 50%.
What are possible causes of urethral syndrome?
- Low bacterial count
- Fastidious organisms (e.g., Ureaplasma)
- Non-infective inflammation
- STIs like Chlamydia trachomatis
What is considered recurrent UTI?
≥3 episodes per year.
Management strategies for recurrent UTI?
- Antimicrobial prophylaxis
- Self-start antibiotics
- Voiding post-intercourse
- Vaginal HRT in postmenopausal women
Role of cranberry in UTI prevention?
Limited evidence; Cochrane review (2008) showed weak benefit only in young women.
What diagnostic method is recommended for children <3 months with fever?
Urine sample + treat as per NICE CG160 guidelines.
Why is imaging important in children with UTI?
To detect underlying renal tract abnormalities (e.g., VUR, obstruction).
Name 5 risk factors for UTI in children.
- Recurrent fever
- Poor urine flow
- Constipation
- Family history of renal disease
- History of UTI (others: VUR, spinal lesions, poor growth, high BP)
Why are antibiotics with high urinary concentration preferred?
They ensure effective eradication of urinary pathogens.
What makes uropathogenic E. coli (UPEC) unique?
- Type 1 fimbriae: bind to mannose (cystitis)
- P fimbriae: bind to kidney cells (pyelonephritis)
- K antigen: inhibits phagocytosis
Classic triad of cystitis symptoms?
Frequency, urgency, dysuria.
Key symptoms of pyelonephritis?
Fever, loin pain, rigors, possible nausea/vomiting.
When is fever absent in UTI?
Often in lower UTI/cystitis.
How often do healthy women urinate per day on average?
3.4 times/day.
