Microbiology Flashcards
definition of UTI?
the presence of micro-organisms in the urinary tract that are causing clinical infection
what is meant by lower UTI?
denotes infection confined to the bladder (cystitis)
what is meant by upper UTI?
denotes infection involving the ureters +/- the kidneys
what is infection of the kidneys referred to as?
pyelonephritis
what is meant by a complicated UTI?
a UTI which is complicated by systemic sepsis or urinary structural abnormalities or stones
meaning of cystitis?
inflammation of the bladder (not always due to infection)
what makes woman more suseptible to UTIs?
- short wide urethra
- proximity of urethra to anus
what else increases the risk of UTI in woman?
- increased sexual activity
- pregnancy
2 routes of infection of the urinary tract?
- ascending infection
- from the bloodstream
what route of infection of the urinary tract is much more common?
ascending route
how does infection travel in the ascending route?
bacteria from bowel, onto perineal skin, to lower end of urethra, then to bladder then ureters then kidneys
how does infection affect the kidney in the bloodstream route?
patient with bacteraemia/septicaemia from another focus of infection, bacteria in blood is seeded into kidneys and gives rise to multiple small abscesses
what organism causes about 70% of UTIs?
E.coli
most common causal organisms in UTI?
- E.coli
- Klebsiella sp
- Enterobacter sp
- Proteus sp
- other coliforms
what is infection with proteus sp associated with?
the formation of stones
how does infection with proteus sp increase the ph of the urine?
it produces urease which breaks down urea to form ammonia
2 types of enterococcus sp that can cause UTI?
- enterococcus faecalis
- enterococcus faecium
what enterococcus sp tends to be resistent to antibiotics and difficult to treat?
enterococcus faecium
what organism is often causative of a UTI in women of child bearing age?
- staphlococcus saphrophyticus
what is pseudomonas auruginosa UTI associated with?
catheters and UT instrumentation
pseudomonas aeruginosa causing UTI is resistent to most oral antibiotics except?
ciprofloxacin
symptoms and signs of UTI?
- dysuria
- frequency of urinarion/nocturia
- haematuria
what symptoms/signs suggest involvement of upper urinary tract?
- fever
- loin pain
- rigors
why is it important to get a mid-stream collection of urine for sample?
bladder urine is normally sterile but urine passed via urethra will be contaminated with bacteria from the perineum or lower urethra so first urine passed is most likely to be contaminated
what should be done before asking patient to give a urine sample?
- wash perineum/urethral meatus with sterile saline
- give patient sterile foil bowl
what are other forms of urine samples (not MSSU)?
- “clean catch” urine: in children and elderly
- bag urine (in babies)
- catheter specimen of urine (CSU)
- subrapubic aspiration
what type of container is optimum for a urine sample and why?
- a boricon container
- contains boric acid (preservative) to stop bacteria multuplying for about 24 hours
if you use a sterile universal container for a urine sample, when must it be given to the lab?
within 2 hours of collection
why does nitrites in urine indicate infection?
some bacteria can reduce nitrates to nitrites - mainly coliforms
what organism will not give a postive nitrite test on dipstick?
enterococcus spp
when is microscopy of urine used?
only done on selected urgent cases
how is bacteria in the urine routinely diagnosed in the lab?
culture of urine
According to the Kass’s criteria, what suggests a significant probable UTI?
> 10 to the 5 organism/ml
according to Kass’s criteria, what would
not significant bacteriuria
according to Kass’s criteria, what does by 10 to the power 4 organism/ml suggest?
- ?contaminates
- ?infection
- repeat specimen
what age group does the Kass’s criteria apply to?
woman of child bearing age
is a mixed growth > 10 to power 5, signififcant?
probably not significant, a genuine UTI will usually be a single organism
what is ESBL?
extended spectrum beta-lactamase
what antibiotics does ESBL make bacteria resistant to?
all cephalosporins and almost all penicillins
what is ESBL carried on?
on a plasmid
antibiotics that may be useful in UTI with ESBL?
- nitrofurantoin, pivmecillinam, fosfomycin, temocillin, meropenum, ertapenam
what last choice antibiotic is carbapenemase producing enterobacteriaceae resistant to?
meropenum
how long should a course of antibiotics be given for in an uncomplicated UTI in women?
3 days
what are the first line antibiotics available for treating UTI?
- amoxicillin
- trimethoprim
- nitrofuranoin
- gentamicin
what can trimethaprim be given as intra-venously?
as cotrimoxazole
2nd line options for treating UTI?
- pivmecillinam
- temocillin
- cefalexin
- co-amoxiclav
- ciprofloxacin
why is amoxicillin not really used as empirical treatment for UTI anymore?
more than 50% of E.coli are now resistant, along with other coliforms
is amoxicillin safe in pregnancy?
yes
what does trimethoprim inhibit?
bacterial folic acid synthesis
can trimethoprim be given in pregnancy?
avoided in first 3 months
what organisms does trimethoprim cover?
most coliforms, staph aureus incl MRSA
what does trimethoprim not cover?
pseudomonas sp
when should nitrofurantoin be avoided and why?
in late pregnancy, breast feeding and in children under 3. cause cause neonatal haemolysis
what does nitrofurantoin not cover?
proteus sp and pseudomonas sp.
why can gentamicin only be used to treat a UTI in hospital?
has to be given IV
can gentamicin be used in pregnancy?
no
what does gentamicin not cover?
enterococci
how long show gentamincin be prescribed for?
for 3 days only
what drug can be useful in complicated UTIs in patients whose renal function is too poor for gentamicin?
temocillin
what is the empirical treatment for a female lower uncomplicated UTI?
trimethoprim or nitrofurantoin orally for 3 days
empirical treatment for uncatheterised male UTI?
trimethoprim or nitrofurantoin orally for 7 days
empirical treatment in the community setting of compicated UTI or pyelonephritis?
- co-amoxiclav or co-trimoxazole for 14 days
empirical treatment in hospital of a complicated UTI or pyelonephritis?
amoxicillin and gentamicin IV for 3 days then stepdown as guided by antibiotic sensitivities
what do you give in complicated UTI or pyelonephritis in hospital if patient is penicillin allergic?
cotrimoxazole and gentamicin IV fr 3 days then stepdown guided by antibiotic sensitivities
when are pregnant woman screened for a UTI?
at 1st antenatal visit
if a bacteria in the urine is left untreated in pregnancy, what % progress to pyelonephritis?
20-30%
