Microbiology of UTI Flashcards
In a normal urinary tract, where is the urine sterile and where might it pick up bacteria?
Sterile - kidney, ureter, bladder
Distal urethra is colonised by bowel flora (coliforms & enterococci)
Define UTI
Presence of bacteria in urine which is causing clinical infection
Define lower and upper UTI
Lower UTI - infection confined to bladder (cystitis)
Upper UTI - infection involving ureters +/- kidney (pyelonephritis)
Define complicated UTI
UTI associated with systemic sepsis OR stones OR urinary tract abnormality
Define bacteriuria
Bacteria in the urine
Nb - common in elderly people with catheters & does not always denote infection
Cystitis is infection of the bladder. T/F
False - inflammation of the bladder; infection is one cause but there are others
Who is at highest risk of UTI?
Women
Catheterised patients
Patients with structural abnormalities of the urinary tract
Why are women more at risk of UTI?
Shorter & wider urethra
Proximity of urethra to anus
Increased risk with sexual activity & pregnancy
Describe ascending infection
Bowel bacteria on perineal skin --> Urethra --> Bladder --> Ureter --> Kidney
Describe bloodstream infection
Bacteraemia/septicaemia –>
Kidneys (multiple small abscesses)
What organisms commonly cause UTI?
E.coli
Klebsiella
Enterobacter
(more rarely proteus & other coliforms)
What are the features of UTI commonly associated with Proteus?
Calculi formation
Foul smelling urine
How does proteus cause the formation of renal stones?
Produces urease which breaks down uric acid into ammonia –> higher blood pH –> formation of salts
What are enterococci? Name two
Types of streptococci which live within the GI tract
Enterococci faecalis and faecium
What types of staph can cause UTI? State whether they are coagulase positive or negative
Staph. saphrophyticus (neg) Staph aureus (pos)
Who gets staph. saphrophyticus infection?
Women of child bearing age
Pseudomonas aeruginosa is a gram negative bacillus of the coliform family. T/F
False - not a coliform
What is pseudomonas aeruginosa infection associated with?
Catheterisation
Instrumentation
How is pseudomonas aeruginosa infection treated?
Ciprafloxacin (resistant to other oral antibiotics)
What are the clinical symptoms and signs of UTI?
Dysuria
Frequency
Nocturia
Haematuria
What are the clinical symptoms and signs of UTI with upper tract involvement?
Fever
Rigors
Flank/loin pain
What is important to remember about collecting urine samples? How is this overcome?
Bacterial contamination from the perineum is common on first samples.
Midstream specimen of urine (MSSU)
Describe how midstream specimen of urine is collected
Perineum/meatus is washed with sterile saline Sterile foil bowl given to patient First pass urine on toilet Mid urine collected in bowl Last pass urine on toilet
Apart from MSSU, how else can urine be collected? When are these indicated
Clean catch - children & elderly
Bag urine - babies
Catheter specimen urine - catheter in
Suprapubic aspiration - outflow obstruction
List one drawback and one positive about bag urine collection?
Often contaminated with bowel flora
Negative culture results are reassuring
Which two containers can be used for urine collection? State the timeframes in which they should be delivered to the lab, respectively
Boricon container - 24 hours (preservative)
Sterile universal container - 2 hours
Which results on dipstick urine testing would indicate infection?
Leukocyte (WBC in urine)
Nitrite (bacteria in urine)
Blood
Protein
Which bacterias will not test positive for nitrites on dipstick?
Enterococci (which is absolutely fabulous because they’re a common pathogen)
Which two tests can be done on the urine in a laboratory? When are these indicated?
Microscopy - urgent cases (look for pus, bacteria & red cells)
Culture - significant bacteraemia suspected
Describe Kass’s criteria for defining urine culture results. Who does this criteria apply to?
> 10^5 organisms/ml - probable UTI
Mixed growth in urine culture is not significant as UTIs are usually caused by one infecting organism. T/F
True - single organism in large majority of patients but may not stand true for those who are catheterised or who have structural abnormalities
What are ESBL producing bacteria?
Extended spectrum beta lactamase producing bacteria (i.e bacteria resistant to all cephalosporins and most penicillins)
Which antibiotics may be useful against ESBL producing bacteria?
Nitrofurantoin (oral)
Temocilin (IV)
(& others)
What are carbapenemase producing enterbacteria (CPE)?
Gram negative coliform bacilli that are resistant to Meropenem (i.e all current antibiotics)
How does CPE resistance spread? What are some strains associated with?
Plasmids
Travel to indian sub-continent
What are the features of an antibiotic useful in treating UTI?
Excreted in high concentrations in urine
Few side effects
Oral
How long a course of antibiotics should be given to uncomplicated lower UTI’s in women?
3 days
What are the first line antibiotics for UTI?
Amoxicillin (IV or oral)
Trimethoprim (oral or IV cotrimoxazole)
Nitrofurantoin (oral)
Gentamicin (IV)
What are the second line antibiotics for UTI?
Pivmecillinam (oral) Temocillin (IV) Cefalexin (oral) Co-amoxiclav (IV, oral) Ciprofloxacin (IV, oral)
Is amoxicillin safe in pregnancy?
Yes
Which organisms will amoxicillin treat?
Enterococci faecalis Some coliforms (50% are resistant)
How does trimethopram work?
Inhibits bacterial folic acid synthesis
Is trimethopram safe in pregnancy?
Avoid in first trimester (3 months)
What is co-trimoxazole a combination of?
Trimethopram and sulphamethoxazole
What risk do sulphonamides carry?
Stevens Johnsons syndrome (i.e toxic epidermal necrolysis)
Which organisms will trimethopram treat?
Most coliforms
Staph aureus
MRSA
NOT pseudomonas
In which clinical presentation of UTI is nitrofurantoin useful? Why?
Lower uncomplicated UTI
Only reaches effective concentrations in bladder urine
Is nitrofurantoin safe in pregnancy?
Avoid in late pregnancy (neonatal haemolysis) , breast feeding and in children
Which organisms will nitrofurantoin treat?
Most coliforms
Staph aureus
MRSA
NOT proteus or pseudomonas
Is gentamicin safe in pregnancy?
No
What does gentamicin toxicity cause? How common is this?
Renal toxicity
8th cranial nerve damage (deafness and balance issues)
Narrow therapeutic index - must be carefully monitored
How is gentamicin administered? What then must be checked?
Once daily IV infusion (7mg/kg)
Must check blood levels 6-14 hours later
Which organisms will gentamicin treat?
Most coliforms
Staph aureus
MRSA
NOT enterococci
When is gentamicin clinically indicated? How long for?
Severe gram negative (i.e coliform) sepsis
NO MORE THAN 3 DAYS
Pivmecillinam is useful in what clinical context?
Lower uncomplicated UTI
What bugs is pivmecillinam effective against?
Resistant coliforms
What bugs is pivmecillinam NOT effective against?
Strep
Staph
Pseudomonas
Enterococci
Can pivmecillinam be used in pregnancy?
Nope
Which bugs is temocillin effective against? Which is it NOT effective against?
Resistant coliforms
Strep
Staph
Enterococci
Pseudomonas
Temocillin is useful in which clinical context?
Complicated UTI/urosepsis where the patients renal function isn’t good enough to introduce gentamicin
Can cefalexin be used in preganancy?
Yes
Why is cefalexin not used if it can be avoided?
Broad spectrum antibiotic increases risk of c.diff infection
Which organisms do cefalexin treat?
Coliforms
Staph
What is co-amoxiclav?
Combination of amoxicillin and clavulanic acid
Is co-amoxiclav safe in pregnancy?
Yes
Which organisms does co-amoxiclav treat? Why is it not used more often?
Staph
Coliforms
Enterococci
C.diff infection risk
When is ciprofloxacin not used?
Young children
Pregnant woman
Why is ciprofloxacin not used more often?
C.diff infection risk because broad spectrum antibiotics
Which organisms does ciprofloxacin treat? Why is worth remembering about this antibiotic?
Pseudomonas
Coliforms
Enterococci
Only ORAL agent that treats pseudomonas
How is female lower UTI treated?
Trimethoprim OR
Nitrofurantoin orally
3 days
How is uncatheterised male UTI treated?
Trimethoprim OR
Nitrofurantoin orally
7 days
How is a complicated UTI/pyelonephritis treated in the community?
Co-amoxiclav OR
Co-trimoxazole
14 days
How is a complicated UTI/pyelonephritis treated in the community?
Amoxicillin/co-trimoxazole AND gentamicin
3 days
Step down treatment
When can you diagnose asymptomatic bacteraemia?
> 10^5 organisms/ml
Asymptomatic patient
NO pus in the urine
How is asymptomatic bacteraemia treated?
It isn’t - especially not in old people
How is asymptomatic bacteraemia treated in a pregnant woman? What happens if you don’t treat?
Antibiotics
May develop into pyelonephritis –>
Intra-uterine growth retardation (IUGR) or premature labour
What is abacterial cystitis/urethral syndrome?
UTI symptoms
Pus in urine
No significant growth in culture
What can the cause of abacterial cystitis?
Early phase of UTI
Urethral trauma
Chlamydia/gonorrhoea causing urethritis
What is honeymoon cystitis?
Urethral trauma due to vigorous sexual intercourse
How can urethral syndrome be treated?
Alkalising the urine for symptomatic relief
Does catheterisation increase the incidence of UTI? What increases the risk?
Yes
Increasing length of catheter
When should catheterised patients be given antibiotics?
> 10^5 organisms/ml
Symptomatic
Giving unnecessary antibiotics to catheterised patients causes what?
Colonisation of catheter with increasingly resistant organisms
