Microbiology of UTI Flashcards
UTI definition?
microorganisms in urinary tract causing clinical infection
where is lower UTI?
confined to bladder (cystitis)
where is upper UTI?
ureters +/- kidneys (pyelonephritis)
describe distribution of bacteria in urinary tract
urine in kidneys and bladder = sterile
lower end of urethra colonised by coliforms and enterococci from large bowel
what is a complicated UTI?
UTI complicated by systemic symptoms or urinary structural abnormality/stones
what is bacteriuria?
bacteria in urine
not always infection - common in elderly patients or patients with catheters
what must be done for bacteriuria?
culture
dipstick not enough
who is UTI most common in?
women (urethra is shorter and wider and closer to anus)
catheterised patients
any abnormality in urinary tract
what can cause an ascending infection?
bacteria from bowel
perianal skin
lower end of urethra
bladder > ureters > kidneys
two common routes of infection in UTI?
ascending (most common)
bloodstream
what can cause bloodstream UTI?
septicaemia
seeded into kidneys
multiple small abscesses
bacteria in urine
when should urine sample be taken?
mid stream
when is dipstick useful?
young people with cystitis
not useful in older people or people with catheters as it doesn’t really tell you much, has lots of false positives
describe coliforms
gram -ve bacilli
biggest cause of UTI?
coliforms
- E.coli (mainly)
- also klebsiella and enterobacter
other non coliform causes of UTI?
pseudomonas
describe E. Coli
endotoxin in LPS layer
fimbriae (help it to attach)
describe proteus
foul smelling (burn chocolate)
produces swarming cultures
causes alkaline urine leading to precipitation of salts
what type of stone does proteus cause?
struite stones (triple phosphate) - due to alkaline urine
describe pseudomonas
gram -ve bacillus
NOT A COLIFORM
associated with catheters and urinary instruments
pseudomonas is resistant to most antibiotics except what?
ciprofloxacin
describe the action of ciprofloxacin
inhibits bacterial DNA gyrase, preventing supercoiling of DNA
not used in children or pregnant women
C. Diff risk
active against pseudomonas, most coliforms, some enterococci but not staph
what commonly causes UTI in hospitals?
enterococcus
- faecalis (mainly)
- faecium
(types of strep which live in the GI tract)
who gets staph saphrophyticus UTI?
women of child bearing age
who gets staph aureus UTI?
if bacteraemia is present
symptoms of UTI?
dysuria
frequency
nocturia
haematuria
what 3 features suggest involvement of upper urinary tract and should be taken seriously?
fever
rigors
loin pain
cystitis vs pyelonephritis?
pyelonephritis more common in systemic disease (diabetes, immunosuppression etc)
pyelonephritis causes more systemic symptoms (fever, chills, malaise, nausea etc)
how is UTI diagnosed?
mid stream specimen collection
- can be suprapubic aspiration
- straight in/out catheter
describe process of collecting mid-stream specimen
wash perineum/urethral meatus with sterile saline (not antiseptic)
give patient wide mouth bowl
first urine passed into toilet
next part of stream collected in bowl without interruption
last urine passes into toilet
urine transferred into lab container
what containers are used for urine specimen?
boricon (stops bacteria multiplying to can last 24 hrs) sterile universal (must reach lab within 2 hrs)
other methods of urine collection?
clean catch (in children or cognitive/physical restriction)
bag urine (used in babies - negative finding is more useful to rule out UTI)
catheter specimen
suprapubic aspiration
purpose of dipstick testing?
leukocyte esterase indicates WBCs in urine
nitrites indicates bacteria in urine
can show protein and blood (not useful for diagnosis)
NOT USED IN ELDERLY OR CATHETER SPECIMENS
lab diagnosis of UTI?
microscopy not really used, can be used after culture
culture usually done
- >10x5 per ml = significant
Kass criteria for culture diagnosis?
10 to power 5 organisms/ml of urine = probable UTI
what is mixed growth?
2 or more organisms on culture
usually not significant if found on culture, even if > 10x5/ml
management of uncomplicated UTI?
3 day course of antibiotic in women
anti-inflammatories can be as good as antibiotics in some cystitis patients
what is abacterial cystitis/urethral syndrome?
symptoms of UTI and pus cells present in urine but no significant growth on culture
can be early phase of UTI, urethral trauma or urethritis due to STI
how can abacterial cystitis be managed?
alkalinising the urine can help symptoms
what is asymptomatic bacteriuria?
significant bacteriuria (>10x5/ml)
no symptoms, codition is detected incidentally
no pus cells in urine
how is asymptomatic bacteria managed?
no antibiotics needed
all pregnant women are screened at 1st antenatal visit
antibiotics are given in pregnancy as can progress to pyelonephritis or lead to growth retardation in foetus
when should catheterised patients be given antibiotics?
only if >10x5 organisms/ml and supporting evidence of UTI (fever, symptoms etc)
common to have colonising bacteria in catheter
empirical female lower UTI management?
nitrofurantoin or trimethoprim orally for 3 days
uncatheterised male UTI management?
get cultures
nitrofurantoin or trimethoprim orally for 7 days
how is complicated UTI or pyelonephritis managed in GP?
co-amoxiclav or co-trimoxazole for 14 days
how is complicated UTO or pyelonephritis managed in hospital?
amoxicillin and gentamicin IV for 3 days
- co-trimoxazole + gentamicin if penicillin allergic
first line for coliforms?
gentamicin IV
first line for enterococcus?
amoxicillin IV
1st line UTI antibiotics?
amoxicillin
trimethoprim
nitrofurantoin
gentamicin
2nd line UTI antibiotics if resistant?
pivmecillinam
co-amoxiclav
ciprofloxacin
main features of gentamicin?
only used in hospital avoid in pregnancy narrow therapeutic index first line for coliforms only give for 3 days
