3: Microbiology of UTI Flashcards
What is a UTI?
Microorganisms in the urinary tract which are causing INFECTIOUS SYMPTOMS
What is a lower UTI?
Confined to the bladder (cystitis)
What is an upper UTI?
Infection involving the ureters AND/OR kidneys
(pyelonephritis)
Urine is normally ___.
sterile
What is a complicated UTI?
Symptoms of UTI (e.g dysuria, urgency, increased frequency) with any of:
SYSTEMIC SYMPTOMS (fever, rigors, N&V…)
RENAL STONES
ANATOMICAL ABNORMALITIES
Does bacteruria mean infection?
Not without symptoms
What is a common site for colonisers of the urinary tract?
Catheter
(Men / women) are more likely to develop UTIs.
women
shorter, wider urethras
sex
pregnancy
People with ___ are more likely to get UTIs.
catheters
What are the two routes of infection in UTI?
Ascending route
Haematogenous
What is the most common organism causing UTIs?
E. coli
Why is E. coli well adapted to causing UTIs?
Common bowel commensal
Have fimbriae (sticky appendages which let them climb all over the place)
Which investigations are used to
a) rule out
b) properly diagnose
UTIs?
a) Dipstick
b) Urine culture
What is the best investigation for UTI?
Urine culture
What are coliforms?
Gram negative bacilli
most commonly E. coli
E. coli is also called a ___ fermenter.
lactose fermenter
along with Klebsiella, Enterobacter
What organisms commonly cause UTIs?
Escherichia
Klebsiella
Enterobacter
Proteus
Pseudomonas
What does E coli produce to cause sepsis?
Endotoxin
What renal disease is Proteus associated with?
Renal stones
particularly struvite stones
Which UTI organism is associated with renal stones?
Proteus
Which type of renal stone is commonly seen in Proteus infection?
Staghorn calculus
Is Pseudomonas a coliform?
NO
but it is a Gram -ve bacillus
What is Pseudomonas UTI associated with?
Catheters
Surgery
How is Pseudomonas UTI treated?
Ciprofloxacin
How does ciprofloxacin work?
Affects bacterial DNA
What are the 4Cs?
Co-amoxiclav
Ciprofloxacin
Clindamycin
Cephalosporins
What’s the difference between Enterobacter and Enterococcus?
Enterobacter is a Gram -ve bacillus
Enterococcus are Gram +ve
What is a Gram positive coccus which causes UTI?
Enterococcus (faecalis)
Staph. saphrophyticus
What is a type of Staphylococcus associated with UTIs in women of child bearing age?
Staph. saphrophyticus
What are the symptoms of UTI?
Dysuria
Haematuria (not always)
Nocturia
Increased frequency
Constitutional symptoms
What symptoms suggest an upper UTI?
Loin pain
Constitutional symptoms
Fever, rigors, N&V…
What type of urine sample is taken to diagnose UTI?
Why?
MIDSTREAM urine sample
First portion of urine will be contaminated by commensals
What is an MSU?
Midstream urine sample
How long after a urine sample is collected must it reach the lab?
< 2 hours
What positives on urinalysis may indicate infection?
Leukocytes
Nitrites
remember dipsticks aren’t the ideal investigation
Why might positive nitrites indicate a UTI?
Coliforms convert nitrates to nitrites
In general, ___ shouldn’t be used to investigate UTI.
What should be used instead?
urinalysis
MSU culture
More than ___ organisms on microscopy indicates UTI.
105
More than ___ organisms on a urine culture indicates infection.
105
Which type of growth in a urine culture is probably not significant?
Mixed growth
i.e more than one organism
What is abacterial cystitis?
Symptoms of UTI without bacterial growth on culture
Why may a patient have abacterial cystitis?
- Early UTI
- Urethral trauma - “Honeymoon cystitis”
- STI
- Patient has taken antibiotics before urine culture collected
What is abacterial cystitis associated with urethral trauma also known as?
Honeymoon cystitis
How may abacterial cystitis be managed?
Stay hydrated
Good hygiene
Refrain from having sex until symptoms stop
Alkalinise urine (symptomatic relief only)
What is asymptomatic bacteriuria?
> 105 organisms in urine but NO SYMPTOMS OF INFECTION
How is asymptomatic bacteriuria treated?
What’s the exception?
Supportively i.e no antibiotics
Pregnant women are given antibiotics
Why are pregnant women given antibiotics if they have asymptomatic bacteriuria?
Complications include:
pyelonephritis
premature labour
growth retardation in child
People with catheters are more at risk of UTI.
When would you give antibiotics to someone with bacteriuria and a catheter?
> 105 organisms AND symptoms of infection
How do you treat an uncomplicated UTI in women?
Nitrofurantoin OR Trimethoprim (3 days)
How do you treat an uncomplicated UTI in men?
Nitrofurantoin OR Trimethoprim (7 days)
Which drug could you give to a pregnant women with an uncomplicated lower UTI?
Cefalexin
because trimethoprim is teratogenic in the 1st trimester and nitrofurantoin is teratogenic in the 3rd (but generally alright to use)
Why are nitrofurantoin or trimethoprim used to treat lower UTIs only?
They aren’t effective in the upper urinary tract
How do you treat a complicated UTI or pyelonephritis in primary care?
Co-amoxiclav (14 days)
How do you treat a complicated UTI in primary care in a patient who is allergic to penicillin?
Co-trimoxazole (14 days)
How do you treat a complicated UTI or pyelonephritis in hospital?
Amoxicillin + Gentamicin IV (3 days)
If a patient in hospital develops a complicated UTI and you treated them with amoxicillin + gentamicin IV for 3 days, what would you then step down to?
Co-trimoxazole PO (4 days)
For a total of 7 days on antibiotics
How do you treat a complicated UTI or pyelonephritis, in hospital, in a patient who is allergic to penicillin?
Co-trimoxazole + Gentamicin IV (3 days)
then step down to
Co-trimoxazole PO (4 days)
Gentamicin can only be used in hospital - why?
Has to be given IV
Is gentamicin safe in pregnancy?
No
How is gentamicin dose calculated?
Weight
What are possible effects of gentamicin toxicity?
Nephropathy
CN VIII damage - hearing loss, balance problems
If a bacterium has beta lactamase, which antibiotics won’t work on it?
Penicillins
Cephalosporins
Carbapenemase-resistant bacteria are resistant to which antibiotics?
All of them
What can be given as an alternative to gentamicin in some patients?
Aztreonam IV
In which trimesters should
a) trimethoprim
b) nitrofurantoin
be avoided?
Why drug could be given to a pregnant women with a UTI instead?
a) 1st trimester
b) 3rd trimester
Cefalexin PO
What is the combined form of trimethoprim which can be given to patients with complicated UTIs?
What is a rare side effect of using it?
Co-trimoxazole
Stevens-Johnson syndrome (severe blistering disease)
