Transcript Document

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list the main microorganisms responsible
from UTI
explain the importance of significant
bacteriuria and quantitative culture method
List the main advantages and disadvantages
of each type ofsample for the laboratory
diagnosis
List the laboratory tests for UTI
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Urinary tract infections are common,
especially among women
20-30% of women have recurrent urinary
tract infections (UTI) at some time in their
life.
UTIs in men are less common and primarily
occur after 50 years of age.
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Although the majority of infections are
acute
short-lived
they contribute to a significant amount of
morbidity in the population.
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Severe infections result in a loss of renal
function and serious long-term sequelae.
In females, a distinction is made between
cystitis, urethritis and vaginitis, but the
genitourinary tract is a continuum and the
symptoms often overlap.
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Coagulase negative staphylococci
Viridans nonhemolytic streptococci
Lactobacilli ♀
Diphtheroids
Non pathogenic Neisseria species
Commensal Mycobacterium species
Yeasts
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Bacterial infection :
usually acquired by the ascending route from
the urethra to the bladder
The infection may then proceed to the kidney.
Occasionally, bacteria infecting the urinary
tract invade the bloodstream to cause
septicemia.
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Bacterial infection :
Less commonly, infection may result from
hematogenous spread of an organism to the
kidney
with the renal tissue being the first part of
the tract to be infected.
From an epidemiological viewpoint,
 UTIs occur in two general settings:
1-community-acquired and
2-hospital (nosocomially) acquired, most often
being associated with catheterization.
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Hospital-acquired UTIs, while less common
than community acquired, contribute
significantly to overall nosocomial infection
rates.
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The Gram-negative rods:
Escherichia coli (the commonest cause of
ascending UTI )
Other members of the Enterobacteriaceae:
-Proteus mirabilis
-Klebsiella, Enterobacter, Serratia spp. and
Pseudomonas aeruginosa
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The Gram-negative rods:
Enterobacteriaceae:
-Proteus mirabilis:
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associated with urinary stones (calculi),
probably because this organism produces a
potent urease,
which acts on urea to produce ammonia,
rendering the urine alkaline.
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The Gram-negative rods:
Enterobacteriaceae:
-Klebsiella, Enterobacter, Serratia spp. and
Pseudomonas aeruginosa :
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are more frequently found in hospitalacquired UTI
because their resistance to antibiotics favors
their selection in hospital patients
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Gram-positive species
Staphylococcus saprophyticus :
◦ especially in young sexually active women.
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Staphylococcus epidermidis and
Enterococcus species are more often
associated with UTI in hospitalized patients
(especially those with AIDS), where multiple
antibiotic resistance can cause treatment
difficulties.
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Gram-positive species
corynebacteria and lactobacilli
Obligate anaerobes: very rarely
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Hematogenous spread to the urinary tract:
other species may be found:
Salmonella typhi,
Staphylococcus aureus
Mycobacterium tuberculosis (renal
tuberculosis).
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rare
hemorrhagic cystitis and other renal
syndromes
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may be recovered from the urine in the
absence of urinary tract
The human polyomaviruses, JC and BK
cytomegalovirus (CMV) and
rubella
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Adenovirus:hemorrhagic cystitis
The rodent-borne hantavirus
mumps and HIV
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Candida spp. and
Histoplasma capsulatum
The protozoan: Trichomonas vaginalis
Schistosoma haematobium : hematuria.
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A variety of mechanical factors predispose to UTI
Pregnancy, prostatic hypertrophy, renal calculi,
tumors and strictures are the main causes of
obstruction to complete bladder emptying
Catheterization is a major predisposing factor for
UTI
A variety of virulence factors are present in the
causative organisms
The healthy urinary tract is resistant to bacterial
colonization
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A key feature is the detection of significant
bacteriuria.
Infection can be distinguished from
contamination by quantitative culture
methods
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the urinary tract is sterile,
the distal region of the urethra is colonized with
commensal organisms,
which may include periurethral and fecal
organisms.
As urine specimens are usually collected by
voiding a specimen into a sterile container, they
become contaminated with the periurethral flora
during collection.
Infection can be distinguished from
contamination by quantitative culture methods.
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the urinary tract is sterile,
the distal region of the urethra is colonized with
commensal organisms,
which may include periurethral and fecal
organisms.
As urine specimens are usually collected by
voiding a specimen into a sterile container, they
become contaminated with the periurethral flora
during collection. Midstream urine (MSU)
Infection can be distinguished from
contamination by quantitative culture methods.
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is defined as 'significant' when a properly
collected midstream urine (MSU) specimen is
shown to contain over 105 organisms/ml.
Infected urine usually contains only a single
bacterial species.
Contaminated urine usually has <104
organisms/ml and often contains more than
one bacterial species
Distinguishing infection from contamination
when counts are 104-105 organisms/ml can
be difficult.
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urine specimens collected from:
Catheters
nephrostomy tubes
suprapubic aspiration directly from the
bladder:
any number of organisms may be significant
because the specimen is not contaminated by
periurethral flora.
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Infection of sites in the urinary tract below
the bladder
by organisms that are not members of the
normal fecal flora:
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numbers in the urine.
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Difficult
'Bag urine' may be collected by sticking a
plastic bag to the perineum in girls or to the
penis in boys
such specimens are frequently heavily
contaminated with fecal organisms.
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with minimum delay
because urine is a good growth medium
for many bacteria and multiplication of
organisms in the specimen between
collection and culture will distort the results
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should be collected before antimicrobial
therapy is started.
If the patient is receiving, or has received,
therapy within the previous 48 h, this should
be stated clearly on the request form.
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a catheter specimen of urine is used
Patients should not be catheterized simply to
obtain a urine sample.
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M. tuberculosis
Schistosoma haematobium
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M. tuberculosis
three early morning urine samples on
consecutive days
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S. haematobium
the last few ml of a late morning urine sample
collected after exercise
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Microscopic examination of urine allows a
rapid preliminary report
Bacteria may be seen on microscopy when
present in the specimen in large numbers.
However, they are not necessarily indicative
of infection,
but may indicate that the specimen has been
poorly collected or left at room temperature
for a prolonged period of time.
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Microscopic examination of urine
The presence of red and white blood cells,
although abnormal, is not necessarily
indicative of UTI.
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infection of the urinary tract and elsewhere
(e.g. bacterial endocarditis)
renal trauma
calculi
urinary tract carcinomas
clotting disorders
thrombocytopenia
Occasionally, red blood cells may
contaminate urine specimens of menstruating
women.
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White blood cells are present in the urine in
very small numbers (e.g. <10/ml) in health
a count of over 10/ml is considered
abnormal, but is not always associated with
bacteriuria.
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Sterile pyuria is an important finding and may
reflect: concurrent antibiotic therapy
other diseases such as neoplasms or urinary
calculi
infection with organisms not detected by
routine urine culture methods.
Renal tubular cells, seen in the urine of
aspirin-misusers, may be confused with white
blood cells. Urinary casts are also indicative
of renal tubular damage.
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A laboratory diagnosis of significant
bacteriuria requires quantification of the
bacteria
Conventional culture methods produce
results within 18-24 h, but rapid methods
(e.g. based on bioluminescence, turbidimetry,
leukocyte esterase/nitrate reductase test,
etc.) are also available.
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storage - the urine must be cultured within 1
h of collection or held at 4°C for not more
than 18 h before culture
antibiotic treatment - in a patient receiving
antibiotics, smaller numbers of organisms
may be significant and may represent an
emerging resistant population; simple
laboratory methods are available to detect
antibacterial substances
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fluid intake - the patient may be taking more
or less fluid than usual, and this will clearly
influence the quantitative result
the specimen - the quantitative guidelines
are valid for MSU specimens; they do not
apply to catheter specimens, suprapubic
aspirates or nephrostomy samples.
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1. Microscopy
2. Quantitative culture
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3.
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Susceptibility testing
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Gram staining→ presence of leukocytes
and microorganisms
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microscopic examination:
Presence of significant number of bacteria in
uncentrifuged urine sample–high magnifaction
power in immersion field; x1000- with Gram stain):
≥ 1 bacterium or bacteria/high power field.
conventionally accepted to correspond ≥105
CFU/mL)
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Culture:
Presence of significant number of bacteria
inuncentrifuged urine sample (quantitative
culture result): ≥ 103 to ≥105 CFU/mL
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Bacteria/ no.of coloni
In asemptomatic patients
105 cfu/ml (male 104): identification and
antibiotic susceptibility test (AST)
104- 105 cfu/ml : contact with clinician if
>2 bacteria is seen
102 cfu/ml : significant if it is taken from
catheter
10 cfu/ml: significant if its suprapubic
aspiration
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E. coli (%50-90)
Other Enterobacteriaceae
S. saphrophyticus (♀)
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P. aeruginosa
Enterococcus spp.
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Other CNS
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