Microbiology of Urinary Tract Infection Flashcards
What part of the renal tract is colonised by bacteria
The distal end of the urethra
What type of bacteria is found in the distal end of the urethra
Coliforms and enterococci from the large bowel
What is the definition of a UTI
The presence of micro-organisms in the urinary tract that are causing clinical infection
What is cystitis
Inflammation of the bladder that ay or may not be caused by an infection
What is a lower UTI
an infection that is confined to the bladder (cystitis)
What is an upper UTI
An infection involving the ureters +/ the kidneys (pyelonephritis)
Why is it important to determine whether the infection is upper or lower
Different antibiotics are used to treat different levels of the urinary tract
What is a complicated UTI
A UTI complicated by systemic sepsis or a urinary structural abnormality or stones
What patients are more likely to have bacteria in their urinary tract but not necessarily an infection
Patients with catheters or elderly patients
What is meant by bacteriuria
The presence of bacteria in the urine
Give 3 reasons that make women more susceptible to UTI than men
Short wide urethra
proximity of urehtra to anus is shorter
increased risk with sexual activity,
pregnancy (uterus presses down on the bladder resulting in incomplete emptying)
Ascending infection is more common. Describe how it occurs
Bowel organisms colonise the perineal skin. they travel to the lower end of the urethra, into the bladder, ureters and then kidneys
Describe how infection occurs from the blood
The patient has bacteraemia/ septicaemia from another focus of infection –> bacteria in blood –> seeded into kidney –> multiple small abscesses –> bacteria in urine
What organism is responsible for 70% of UTI
E Coli
What are almost all causal organisms
Gram negative bacilli
What are some other causal organisms
Coliforms
Klebstelle sp.
Enterobacter sp.
Proteus sp.
What is protest sp. associated with
the formation of stones (calculi)
They produce urease which changes urinary pH which causes precipitation of salts and this can result in the formation of stones
there are 2 common forms of Enterococcus spp.
Name them
What is more difficult to treat and why
Enterococcus faecalis and enterococcus faecium
Faecium is more difficult to treat as it is more resistant to antibiotics
What organism usually affects women of child bearing age
Staphylococcus saphrophyticus
What is pseudomonas aeruginosa associated with
UT instrumentation or catheters
What is the antibiotic that seems to be sensitive to pseudomonas aeruginosa.
What is the disadvantage of using it
Ciprofloxacin
Associated with C diff infection
How does pseudomonas aeroginosa behave differently to other coliforms
It grows aerobically
What are the signs and symptoms of a UTI
dysuria
frequency of urination
nocturia
haematuria
What are some signs of an upper urinary tract infection
fever
loin pain
rigors
How is the best specimen collected
Wash perineum / urethral meatus with sterile saline (not antiseptic)
Allow patient to pass first part in toilet. Collect second part which should have less organisms and not just urethral organisms
Pass last urine in toilet
Why should antiseptic not be used to wash the perineum
It can inhibit bacteria growth which may affect lab results
What is the difficulty with bag urine collection
It is often contaminated with bowel flora
A negative culture result is more useful than a positive as it can exclude infection from the differential
What might a clinician do lift he bag urine is positive
Suprapubic aspirate of urine
How is urine collected from a catheter for culture
Take from a collection port - not the bag
What is the best container to collect urine for sending to the lab
Boricon container (red top) It contains the preservativeve boric acid which will stop bacteria multiplying for 24 hours
When might LEU be raised on dipstick
Catheterised patients
What organism does not give a positive nitrite test
Enterococci
If a patients urinalysis shows LEU, when should you send a sample
Only if they have signs and symptoms as well
What should we look for on microscopy of urine
Not done routinely but when we do we look for: presence of polymorphs (pus cells), bacteria +/- RBCs
When is a plate insignificant of a urine infection
10^3
When is a plate of urine definitive for UTI
10^5 organisms or more but usually only 1 organism shows huge numbers (not huge numbers of various organisms)
When might a urine plate be contaminated or show signs of an early UTI
10^4 organisms
Test should be repeated
What is the problem of using Kass’s Criteria
It only applies to women of child bearing age
What is ESBL
Extended spectrum beta lactamase - this is an enzyme that breaks down the beta lactic rings in almost all cephalosporins and penicillins
Where is ESBL carried
on a plasmid
What are some antibiotics that may be useful for treating ESBL-producing bacteria
Nitrofurantoin - oral Pivemecillinam - oral Fosfomycin - oral Tmocillin-IV Meeropenem - IV Ertapenem -IV
What is though to be one of the causes for the increasing incidence of ESBL producing bacteria
Imported chickens - they contain antibiotic strains
What are carbapenemase- producing enterobacteriaceae (CPE)
Gram negative (coliform) bacilli that are resistant to meropenem --> basically resistant to all antibiotics This is the last choice antibiotic
Why did CPE become resistant
A lot of organisms are found in Asia. Uncontrolled use of antibiotics there
What are 4 ideal components of an antibiotic
Excreted in urine in high concentration
Oral
Inexpensive
Few side effects
Why is trimethoprim the first line AB in women
It inhibits bacterial folic acid synthesis - a range of organisms can be treated
Why is trimethoprim contraindicated in the 1st trimester of pregnancy
It inhibits folate synthesis –> spinabifida is associated with low levels of folic acid in pregnancy
How can trimethorprim be given
As co-trimoxaxole (IV or oral)
When would nitrofurantoin be given
In lower uncomplicated UTI -
When should nitrofurantoin be avoided
Late pregnancy
Breastfeeding
Why can Nitrofurantoin only be used for uncomplicated lower UTI
It is only activated in the urine
Why should gentamicin be avoided in pregnancy
Risk of hearing problems and kidney problem in the fetus
VIIIth nerve damage - deafness and balance problems
How long should gentamicin be prescribed for
3 days only - not 3 doses
What is the main advantages of using pivmecillinam
Very beta-lactamase stable - high activity against very antibiotic-resistant coliforms that produce extended spectrum beta-lactamases (ESBLs)
Less of a risk of C diff
When would Temocillin be used
It is useful for patients whose renal function is too poor for gentamicin but is not as effective
When is Cefalexin used
During pregnancy
What is co-amoxiclav made up of
amoxicillin and clavulanic acid
What does Ciprofloxacin do
Inhibit bacterial DNA gyros which prevents supercoiling of bacterial DNA
Who should not receive ciprofloxacin
Pregnant women or young children
What is the antibiotic of choice for a female lower UTI
Trimethoprim or nitrofurantoin
oral
3 days
What is the antibiotic of choice for an uncatheterised male UTI
Trimethoprim or nitrofurantoin orally
7 days
What is the antibiotic used for a complicated UTI or pyelonephritis (GP)
Co-amoxiclav or co-trimoxazole
14 days
What is the antibiotic used for a complicated UTI or pyelonephritis (hospital)
Amoxicillin and gentamicin IV for 3 days
Co-trimoxazole and gentamicin if penicillin allergic
Stepdown as guided by antibiotic sensitivities
Why are pregnant women treated for asymptomatic bacteriuria but other patients are not
If pregnant women are left untreated, 20-30% progress to pyelonephritis
This may lead to intra-uterine growth retardation or premature labour
What might help symptoms of bacterial cystitis / urethral syndrome
Alkalinising the urine may help
