Flashcards in L75 – Urinary Tract Infections Deck (90):
Female: male ratio of UTI?
Female:male – 30:1
What is associated with most hospital acquired UTI?
30-40% of all hospital-acquired infections (HAI):
often associated with use of catheters causing UTI
UTI in adult men is rare unless what condition occurs?
Obstruction of urethra from benign prostatic hyperplasia (BPH), e.g. in elderly
What is the main host defense against UTI?
Flushing effect of urine:
>> Emptying the bladder flushes out bacteria in bladder, urethra
>> Anything that interferes with flushing increases risk of UTI
What host defense decreases the severity and chance of UTI complications?
Immunity decreases severity, chance of complication:
Action of bacteria causing infection to bladder?
2) colonize on urinary orifice
3) infect and ascent from urethral opening to bladder in retrograde manner
UTI pathogens are usually found where?
mostly enteric / skin, e.g. fecal flora
What is UPEC?
Extraintestinal pathogenic E.coli
Apart from E.coli, name some other UTI bacteria?
Name some roles of virulence factors in TUI bacteria?
2 structures of bacteria used to adhere to mucosa?
What is the structure that UPEC uses to adhere to mucosa?
Type 1, pyelonephritis-associated (P) fimbriae
Give 2 examples of immune evasion structure used by UPEC?
Give 2 examples of toxins secreted by UPEC?
hemolysin, aerobactin protease
What is the role of flagella in UPEC?
flagella provides mobility > ascending infection
Give 2 sources of E.coli that can cause UTI?
extraintestinal pathogenic E. coli:
1) contaminated / raw / improperly cooked food
2) retail chicken meat products, eggs
If E.coli has no zoonosis potential, what is expected from a resistance profile between human and poultry bacteria?
expect human-susceptible to cluster with human-resistant,
poultry -susceptible to cluster with poultry- resistant
What is the resistance profile of E. coli that causes UTI? What does this imply?
expect human-susceptible to cluster with human-resistant, but not seen in this
case - human and poultry strains mix
suggests route of transmission can be from
poultry-resistant / poultry-susceptible
>> E. coli has zoonosis potential
What factors predispose UTI?
Length of urethra
Mechanical factors causing trauma to mucosa
Genetic factor e.g. density of bacterial receptors
Hormonal effect on mucosa
Explain how length of urethra affects risk for UTI?
Length of urethra before reaching bladder:
long in male, short in female
Females are at much higher risk
Give examples of mechanical factors causing trauma to mucosa, casuing UTI?
Contraceptive diaphragm (compress posterior part of
urethra >> help ascent of bacteria)
Explain the effect of hormones on mucosa?
menopause: hormones (especially estrogen) decreases
>> atrophy of mucosa facilitate bacterial adherence
Explain how pregnancy can lead to increased spreaad of UTI?
>> dilatation, decreased peristalsis of ureter
>> compress on urethra and incompletely emptying
What is neurogenic bladder and what are the sonsequences?
bladder dysfunction (flaccid or spastic) caused by neurologic damage
Risk of serious complications (eg, recurrent infection, vesicoureteral reflux, autonomic dysreflexia)
factors that can cause poor emptying of bladder?
How does urinary catheter increase spread of UTI?
nidus (focus of infection) for persistence
How does stones increase UTI spread?
Obstruction of urethra >> impaired flushing
How does diabetes increase risk of UTI?
What causes reflux which increases chances of UTI?
Incompetent ureterovesical valves (functional / anatomical)
How does bacteria in urinary tract reach blood?
Bladder > kidney > blood
Summarize all the factors that increases spread of UTI
Foreign body obstruction
Dilation and decreased peristalsis of ureter
Virulence factor that causes inflammation?
Explain how UTI increases formation of kidney stones?
Some bacteria in urine produces urease
Urease converts urea to NH3 and raises urine pH
Normally acidic urine becomes alkaline, causing salts to precipitate
>> form stones
2 classes of UTI?
Uncomplicated and complicated
What is the most dominating pathogen to cause UTI?
Definition of uncomplicated UTI?
Infection in a structurally and neurologically normal urinary tract
Affect healthy individuals
Which organs are involved in uncomplicated UTI?
Bladder and kidney
Definition of complicated UTI?
UTI associated with factors that compromise the urinary tract or host defense (e.g. urinary obstruction, neurogenic bladder...etc)
What can cause recurrent infection>?
Relapse or Reinfection
Differentiate relapse from reinfection?
Relapse = same bacterial strain persist to infect
Reinfection = new infection by a different organism / strain
What is urosepsis?
sepsis caused by UTI
Symptoms of acute pyelonephritis?
High fever, loin pain
Difference between acute pyelonephritis and glomerulonephritis?
glomerulonephritis: mainly autoimmune
Acute pyelonephritis: caused by bacterial infection
Which patients are likely to have perinephric abscess? What is it?
Spread from kidney to adjacent fascia
In patient with underlying disease, e.g. poorly
controlled diabetes mellitus
What is cystitis?
Inflammation of Bladder lining (e.g. mucosa, urine; not outside)
Symptoms of cystitis?
urinary urgency and frequency, dysuria, suprapubic discomfort
What constitutes asymptomatic bacteriuria?
No symptoms but diagnosed in laboratory diagnosis
Symptoms of acute and chronic prostatitis?
Acute = fever, perineal pain
Chronic= non-specific and hard to diagnoser
What is pyuria?
inflammatory response due to infection > abnormally high number of WBC /
How is pyuria detected?
Use urine strip:
Leukocyte esterase (from host) react with substrates in strip to produce purple
How may results from urine strip be wrong?
- Some drugs (e.g. cephalexin), high glucose level may interfere with chemical reaction =
- Positive result may occur from contamination of specimens by vaginal discharge
What is the nitrite detection test for? How does it work?
Some bacteria possess nitrate reductase
> can reduce nitrate (NO3-) in urine to nitrite (NO2)
> nitrite reacts with substrates in strip to produce uniform pink color
Give 2 reasons why the nitrite detection test is not definitive for UTI ?
Some bacteria (e.g. enterococcus) do not have the enzyme for reducing nitrate to nitrite
Urine may not be retained in the bladder for long enough for bacteria to reduce nitrate (e.g. frequent
How to differentiate contamination / genuine
use quantitation / semi-quantitative culture
Explain how the count of bacteria can be used to differentiate infection from contamination?
Cut threshold cut-off
Infected women (significant bacteriuria): >= 10^ 5 bacteria/mL of urine
Why do uninfected women still have bacteria in urine?
because urine passes through the portion of mucosal surface in urethra that is colonized by
What is the medium for UTI?
cysteine lactose electrolyte deficient (CLED) agar
Why is CLED used?
inhibits swarming (no expression of motility in
>> create localized, colony morphology
** hence why blood agar is not used **
What is the positive and negative results for CLED agar?
+ve = ferment lactose = yellow
-ve = doesnt ferment lactose = white
Give 2 methods to put urine on agar culture to detect bacterial load?
Standard calibrated loop
Dip paper strip vertically to line > touch urine to agar surface
What is the cfu indicating significant growth of bacteria?
>1 x 10^5 Colony count per mL of urine
Name other agar (not CLED) for detecting urine bacterial load?
incubate for 24h> determine
the number of bacteria
Name ways to collect urine ?
MSU (mid-stream urine)
Clean-catch urine (baby)
Pediatric urine bag
CSU (indwelling urine catheter)
Suprapubic tap urine
What is the bacterial cfu in suprapubic tap urine sample?
Any growth = UTI
Not the usual 10^5 colonies per mL
Which symptomatic patients might not produce urine with 10^5 cfu/ml?
Women with uncomplicated cystitis
Under what circumstance does low cfu still count as clinically significant?
If the colony is pure growth (esp. E.coli)
2 reasons for urine samples to produce false positive results?
Heavy colonization of vagina
Delay transport >2h
Give one reason how a urine sample creates false negative result?
Cleaning with antiseptic > contaminate urine and lower bacterial load
No UTI symptom = no urine culture and treatment except in which 3 cases?
Pregnant women (if not treated: 20-30% risk of progression to acute pyelonephritis)
Before urological operation (e.g. transurethral resection of enlarged prostate gland)
Children (age <5 years), with vesico-ureteric reflux of urine back into kidney (e.g. valve defect)
Asymptomatic bacteriuria is common is which patients?
Most recuurent UTI is caused by what?
Most do not have structural abnormality
What host or microbe factor can increase chances of recurrent UTI?
1. Unusually receptive uroepithelial cells; or
2. Colonization by ’stick strains’ of E. coli
What criteria is needed for urological evaluation in young women, which in not routine or cost-effective?
2 things needed:
1) Recurrent UTI
2) Any one of the following conditions:
-Hematuria between infections
Risk factors for acute bacterial prostatitis?
Unprotected anal intercourse
Indwelling urinary catheter use
What are the clinical presentations of Acute bacterial prostatitis (ABP)?
High fever + septic shock
Dysuria and urinary frequency
Very tender prostate
What causes urinary retention in ABP?
Obstruction from acute edema of prostate
What is the urine culture cfu?
>= 10^5 cfu/ml
What are the 2 tests to confirm Chronic bacterial prostatitis?
Positive 4 glass or 2 glass test
What causes chronic bacterial prostatitis?
Relapsing UTI by the same organism
Name the 4 bacteria that are accepted pathogens for acute and chronic bacterial prostatitis?
E. coli (70%)
What are some associated conditions of chronic bacterial prostatitis?
Retrograde spread of bacteria into prostatic ducts
Previous instrumentation (e.g. ultrasound probe)
Is ultrasound good for diagnosis of bacterial prostatitis?
Ultrasound imaging is not indicative (confused with BPH)
Treatment of CBP?
Treatment: 6-12 weeks antibiotics
What are in the 4 samples in the 4 glass test/ Stamey's technique? Which samples have pathogen ?
1. VB1 = first 10mL urethral urine voided
2. VB2 = mid-stream culture
3. Expressed prostatic secretion (EPS)
4. VB3: first 10mL voided after massage
3rd and 4th samples have bacteria
What induces EPS release from prostate?
Massage prostate for ~1 min
Limitation of 4 glass test for CBP?
Difficult to perform
Limited sensitivity for
What is in the 2 samples of the 2 glass test? which one contains bacteria?
VB1: 1st voided 10mL urine
Why is semen collected in 2 glass test?
Repeat if ejaculate yields Gram-positive bacteria:
Ejaculate comes from seminar vesicle, passes through prostate
>> carries infective organism