Microbiology of UTI's Flashcards
What is the definition of a UTI? what is the difference between a lower and upper UTI?
presence of microorg.s in tract causing an environmental infection
Lower - confined to bladder
Upper - involves ureters +/- kidneys
what is the definition of a complicated UTI?
UTI + systemic sepsis or urinary structural abnormality or stones
what is:
- bacteruria
- cystitis?
Bacteruria - bacteria in urine (not always a UTI)
cystitis - inflammation of bladder
what is the colonisation of the normal urinary tract?
Kidneys/ureter/bladder - sterile
Lower urethra - coliforms/enterococcus
Why are women more susceptable to UTI’s? what increases the risk of UTI’s?
Short (5cms) wide urethra that’s in close proximity to the anus
Increased risk if: pregnant, sexual intercourse, catheter, abnormal urinary tract
What are the two different routes of UTI?
Ascending or from bloodstream due to bacteraemia/septicaemia
what are the 4 different coliforms assoc. with UTI’s?
coliforms = gram -ve bacilli
-e.coli
-klebsiella
-enterobacter sp
-proteus sp
other coliforms
What is a UTI due to proteus assoc. with?
stone formation: produces urease that breaks down urea = ammonia = increases the urinary pH = precipates salt
What gram -ve bacilli that is not considered a coliform can cause UTI’s? What are UTI’s due to this organism assoc. with?
pseudomonas aeruginosa
- assoc. with catheters and other instrumentation
- resistant to most abiotic except ciprofloxacin
What gram positive organisms cause UTIs?
- Enterococcus
- staphylococcus saphrophyticus
- staph aureus
Enterococcus:
- what type of organism is this?
Gram positive streptococci that occur as diplococci or in strips
-gamma haemolytic (do not cause haemolysis)
Staphylococcus saphrophyticus
- What type of organism is this?
- what demographic of patients does this affect?
coagulase negative staphylococcus
-affects women of child bearing age
What are the 7 s/s of UTI?
Dysuria frequency nocturia haematuria fever loin pain rigors
what type of urine sample is important when testing for UTI’s in general?
MSSU
When would: -clean catch urine -bag urine -catheter specimen -suprapubic aspiration be used to collect a urine sample?
Clean catch: babies/elderly
Bag urine: attach a bag to urethral meatus in babies - often contaminated with bowel flora so if positive have to do a suprapubic aspiration to confirm
catheter specimen - aspirate from tube
suprapubic aspiration - babies/young children
What is the difference between a boricon container and a sterile universal container when sending urine?
Boricon (red top) has preservative that works for about 24hours
sterile universal container must reach lab within 2 hours
What different dipstick urine tests would suggest UTI?
- leukocyte esterase
- nitrites (some bacteria convert nitrates to nitrites)
- protein/blood
How does the lab diagnose UTI’s?
-microscopy urine if urgent: look for polymorphs (pus cells), bacteria +/- RBCs
- Culture urine on all samples: look for a significant bacteruria (only UTI if there’s a significant amount colonisation of 1 bacteria)
- if there is a mixed growth probably not significant (doesn’t apply for abnormal tracts)
What is kess’s criteria?
applies to women of childbearing age:
>10^5 organisms/ml = significant (probable UTI)
<10^3 organisms/ml = not significant
10^4 organisms/ml = contaminated? infection? repeat
What is the empirical treatment for female lower UTI?
Trimethoprim/nitrofurantoin - 3 day course
What is the empirical treatment for an uncatheterised male lower UTI?
trimethoprim/nitrofurantoin - 7 day course
What is the empirical treatment for complicated UTI/pyelonephritis in the community?
co-amoxiclav or cotrimoxazole - 14days
What is the empirical treatment for a complicated UTI/pyelonephritis in the hospital setting?
amoxicillin and gentamicin IV - 3 days
(if allergic penicillin cotrimoxazole instead of amox.)
(cotrimoxazole is IV trimethoprim)
Trimethoprim:
- how does it work?
- when to avoid?
- what organisms does it cover?
inhibits folic acid synthesis of bacteria, good conc. in urine and prostate, cheap
-avoid in first trimester pregnancy
Organisms:
- range but not pseudomonas
- most coliforms/s. aureus including MRSA
Nitrofurantoin:
- when can this only be used and why?
- when to avoid
- what organisms does it cover?
- Can only be used in lower uncomplicated UTI as only reaches effective conc. in the bladder
- avoid in late pregnancy, breast feeding and <3mths babies
Organisms:
- not proteus/pseudomonas
- most coliforms, enterococci, staph. aureus inc MRSA
Gentamicin:
- how is this given? when is a level taken?
- how long can it be prescribed for?
- risks?
- organisms covered?
Given IV in hospital, 7mg/kg once daily and then measure blood levels 6-14hrs later
-prescribe for 3 days only
Risks:
- avoid in pregnancy
- narrow therapeutic index, toxicity causes renal and VIIIth CN damage
Organisms:
- most coliforms
- pseudomonas
- staph aureus inc MRSA
- not enterococcus
Antibiotic resistance in UTI’s, lots of organisms are becoming antibiotic resistant - what type of bacteria that causes UTI’s are becoming antibiotic resistant? what abiotics are useful in these scenarios?
Extended spectrum B lactamase (ESBL) producing bacteria
Useful antibiotics:
- temocillin (also used in those who can’t take gent.)
- pivmecillinam (not recommended in pregnancy)
Which abiotic if amox and trimeth. resistant? is this safe in pregnancy?
- Cephelexin
- safe in pregnancy
- trying to reduce use as high risk recurrant UTIs post-treatment
If there is a significant bacteruria with no pus cells and asymptomatic in a non-pregnant patient what is the treatment?
nothing
In pregnancy - why are women screened for asymptomatic bacteruria?
All pregnant women are screened at the first antenatal visit and if they are left untreated 20-30% progress to pyelonephritis (which can lead to intra-uterine growth retardation or premature labour)
What is the treatment for UTI/asymptomatic bacteruria in pregnancy
1st or 2nd trimester nitrofurantoin MR 100mg bd or 50mg qds.
3rd trimester trimethoprim 200 mg bd (unlicensed).
2nd line (any trimester) cefalexin 500 mg tds or as per sensitivities.
Treat for 7 days and sample for test of cure
What is abacterial cystitis/urethral syndrome? What are the causes of this?
UTI symptoms bu no significant growth (pus cells might be present)
Causes:
- early phase UTI
- urethral trauma ‘honeymoon’
- urethritis caused by chlamydia/gonorrhea
(alkalising urine may help)
When would an antibiotic be considered for a catheterised patient?
-if significant culture and symptoms (otherwise increasingly resistant microorg. will colonise)
