Microbiology of UTIs Flashcards
What is a UTI?
Presence of micro-organism in urinary tract that result in clinical infection
What does the lower urinary tract refer to?
Bladder
What does upper urinary tract consist of?
Ureters and kidneys
Which organisms normally colonise the lower urethra?
Coliforms and enterococci from the large bowel
What is a complicated UTI?
UTI complictaed by systemic symptoms or urinary structural abnormalities/stones
What are the main risk factors for UTI?
- Female
- Short wide urethra
- Proximity of urethra to anus
- Increased risk with sexual activity
- Pregnancy
- Catheterised patients
- Abnormalities of the urinary tract
What is the most common causative pathogen which causes UTI?
E. coli
What is the most common mode of UTI infection?
Ascending infection
(bloodstream less common)
Which test is best for confirming the causative pathogen in UTI?
Culture
(dipstick gives much less information and poor confirmation)
What causes sepsis in gram negative bacteria?
Endotoxins
Where do endotoxins live in gram negatives?
Lipopolysacchraide layer (strores LPS endotoxin)
Proteus infection is associated with causing what when assoictaed with UTI?
Renal calculi
(Produces urease which breaks down urea to form ammonia, which increases urinary pH - precipitation of salts)
Pseudomonas is a gram negative _________ but not a ____________
Pseudomonas is a gram negative baclillus but not a coliform
Which causes is P. aeruginosa associated with when causing UTIs?
Instrumentation and catheters
Which antibiotic is P. aeruginosa not resistant to?
Ciprofloxacin
How does ciprofloxacin function?
Inhibits bacterial DNA gyrase, which prevents “supercoiling” of bacterial DNA
What is the most common cause of gram positive UTI?
Enterocci
(faecalis > faecium)
Which gram postive organism commonly affects women of child bearing age and causes UTI?
S. saphrophyticus
What are the signs and symptoms of UTI?
- Dysuria (pain passing urine)
- Frequency of urination
- Nocturia
(Haematuria, Fever, Loin pain associated with upper UTI)
What is the best way to gain a sample?
Midstream sample
(need bladder sample)
(Suprapubic aspiration and Straight (in/out) catheter good scientifically, but bad for patient)
Which patients should not have their urine dipsticked for infection diagnosis?
Elderly
Catheterised patients
In which instance would asymptomatic bacteruria be tretaed and why?
Pregnancy
- Intra-uterine growth retardation
- Premature labour
- Increased risk of pyelonephritis
How is a female lower UTI treated?
Trimethoprim or nitrofurantoin orally 3 days
How is an uncatheterised male UTI treated?
Trimethoprim or nitrofurantoin orally 7 days
How is a complicated UTI treated in the GP setting?
Complicated UTI or pyelonephritis (GP)
Co-amoxiclav or co-trimoxazole (14 days)
How is a complicated UTI treated in the hospital setting?
Complicated UTI or pyelonephritis (Hospital)
Amoxicillin and gentamicin IV for 3 days
(cotrimoxazole and gentamicin if penicillin allergy), stepdown as guided by antibiotic sensitivities
What are the risks of gentamicin toxicity?
VIII nerve palsy (dizziness, hearing loss)
Renal toxicity
Which drug is the choice for ESBLs?
Meropenem
Which drug is generally used if gentamicin cannot be used?
Aztreonam
(also used when eGFR < 20)
Why is trimethoprim avoided in the first trimester of pregnancy?
Inhibition of folic acid synthesis
Can increases neural tube defects
When is nitrofurantoin avoided?
- Avoid in late pregnancy (can cause neonatal haemolysis)
- Breast feeding
- Children <3 months old
