Microbiology of UTIs

Question 1

What is a UTI?

Answer 1

Presence of micro-organism in urinary tract that result in clinical infection

Question 2

What does the lower urinary tract refer to?

Answer 2

Bladder

Question 3

What does upper urinary tract consist of?

Answer 3

Ureters and kidneys

Question 4

Which organisms normally colonise the lower urethra?

Answer 4

Coliforms and enterococci from the large bowel

Question 5

What is a complicated UTI?

Answer 5

UTI complictaed by systemic symptoms or urinary structural abnormalities/stones

Question 6

What are the main risk factors for UTI?

Answer 6

1. Female
   
   • Short wide urethra
   • Proximity of urethra to anus
   • Increased risk with sexual activity
   • Pregnancy
2. Catheterised patients
3. Abnormalities of the urinary tract

Question 7

What is the most common causative pathogen which causes UTI?

Answer 7

E. coli

Question 8

What is the most common mode of UTI infection?

Answer 8

Ascending infection

(bloodstream less common)

Question 9

Which test is best for confirming the causative pathogen in UTI?

Answer 9

Culture

(dipstick gives much less information and poor confirmation)

Question 10

What causes sepsis in gram negative bacteria?

Answer 10

Endotoxins

Question 11

Where do endotoxins live in gram negatives?

Answer 11

Lipopolysacchraide layer (strores LPS endotoxin)

Question 12

Proteus infection is associated with causing what when assoictaed with UTI?

Answer 12

Renal calculi

(Produces urease which breaks down urea to form ammonia, which increases urinary pH - precipitation of salts)

Question 13

Pseudomonas is a gram negative _________ but not a ____________

Answer 13

Pseudomonas is a gram negative baclillus but not a coliform

Question 14

Which causes is P. aeruginosa associated with when causing UTIs?

Answer 14

Instrumentation and catheters

Question 15

Which antibiotic is P. aeruginosa not resistant to?

Answer 15

Ciprofloxacin

Question 16

How does ciprofloxacin function?

Answer 16

Inhibits bacterial DNA gyrase, which prevents “supercoiling” of bacterial DNA

Question 17

What is the most common cause of gram positive UTI?

Answer 17

Enterocci

(faecalis > faecium)

Question 18

Which gram postive organism commonly affects women of child bearing age and causes UTI?

Answer 18

S. saphrophyticus

Question 19

What are the signs and symptoms of UTI?

Answer 19

1. Dysuria (pain passing urine)
2. Frequency of urination
3. Nocturia

(Haematuria, Fever, Loin pain associated with upper UTI)

Question 20

What is the best way to gain a sample?

Answer 20

Midstream sample

(need bladder sample)

(Suprapubic aspiration and ­Straight (in/out) catheter good scientifically, but bad for patient)

Question 21

Which patients should not have their urine dipsticked for infection diagnosis?

Answer 21

Elderly

Catheterised patients

Question 22

In which instance would asymptomatic bacteruria be tretaed and why?

Answer 22

Pregnancy

1. Intra-uterine growth retardation
2. Premature labour
3. Increased risk of pyelonephritis

Question 23

How is a female lower UTI treated?

Answer 23

Trimethoprim or nitrofurantoin orally 3 days

Question 24

How is an uncatheterised male UTI treated?

Answer 24

Trimethoprim or nitrofurantoin orally 7 days

Question 25

How is a complicated UTI treated in the GP setting?

Answer 25

Complicated UTI or pyelonephritis (GP)

­Co-amoxiclav or co-trimoxazole (14 days)

Question 26

How is a complicated UTI treated in the hospital setting?

Answer 26

Complicated UTI or pyelonephritis (Hospital)

­Amoxicillin and gentamicin IV for 3 days

­(cotrimoxazole and gentamicin if penicillin allergy), stepdown as guided by antibiotic sensitivities

Question 27

What are the risks of gentamicin toxicity?

Answer 27

VIII nerve palsy (dizziness, hearing loss)

Renal toxicity

Question 28

Which drug is the choice for ESBLs?

Answer 28

Meropenem

Question 29

Which drug is generally used if gentamicin cannot be used?

Answer 29

Aztreonam

(also used when eGFR < 20)

Question 31

Why is trimethoprim avoided in the first trimester of pregnancy?

Answer 31

Inhibition of folic acid synthesis

Can increases neural tube defects

Question 32

When is nitrofurantoin avoided?

Answer 32

1. Avoid in late pregnancy (can cause neonatal haemolysis)
2. Breast feeding
3. Children <3 months old