Lec 2 Urinary Tract Infection UTI is a bacterial infection that affects any part of the urinary tract A urinary tract infection occurs where bacteria and white blood cells are present in the urine of a patient with symptoms of infection of the urethra urinary bladder or the kidney ID: 915189
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Slide1
Urinary tract infection (UTI)
Lec
. 2
Slide2Urinary Tract Infection (UTI)
is a bacterial infection that affects any part of the urinary tract. A urinary tract infection
occurs where bacteria and white blood cells are present in the urine of a patient with symptoms of infection of the urethra, urinary bladder, or the kidney.
The most common type of UTI is acute cystitis often referred to as a bladder infection. An infection of the upper urinary tract or kidney is known as
pyelonephritis
.
Bacteriuria
occurs when
bacteria
are present in the urine;
pyuria
occurs when
white blood cells
are present in the urine.
The
bacteria that cause urinary tract infections are usually of fecal origin (e.g.,
Escherichia coli
).
Slide3Etiology
The
most common cause of urinary tract infections (i.e.,
urethritis
, cystitis, and
pyelonephritis
) is
Escherichia coli
.
Staphylococcus
saprophyticus
is the second most common cause of these infections in
females between the ages of 13 and 40
.
In
complicated cases of urinary tract infections such as those resulting from anatomic obstructions or from catheterization, the most common causes are
E. coli
,
Klebsiella
pneumoniae
, Proteus mirabilis, Enterococcus
, and
Pseudomonas
aeruginosa
.
Slide4Manifestations
Urethritis
:
is an infection of the urethra that causes pain and discomfort during voiding (
dysuria
).
Cystitis:
is an infection of the urinary bladder. Signs and symptoms of cystitis include urgency and frequency of urination, voiding small volumes of urine, and supra pubic tenderness just before or immediately after voiding.
Pyelonephritis:
is
an infection of the urinary tract ascends the ureters to enter the kidneys, the signs and symptoms include fever, flank pain and tenderness, cost vertebral angle tenderness, nausea and vomiting.
Slide5Urine Culture
Urine
is the specimen most frequently submitted for culture. The most common sites of urinary tract infection (UTI) are the urinary bladder (cystitis) and the urethra. From these sites the infection may ascend into the
ureters
(
ureteritis
) and subsequently involve the kidney (
pyelonephritis
). Females are more prone to infection of the urinary tract than are males.
Factors
that increase female susceptibility to UTI:
Short length of the urethra
Urethral contamination by rectal pathogens
Vestibular colonization by pathogenic bacteria
Decreased urethral resistance after menopause
Slide6In both males and females, UTI may be asymptomatic, acute, or chronic.
-
Asymptomaic
infection can be diagnosed by culture.
-Acute UTI is more frequently seen in females of all ages; these patients are usually treated on an outpatient basis and are rarely admitted to hospital.
-Chronic UTI in both males and females of all ages is usually associated with an underlying disease (e.g.
pyelonephritis
, prostatic disease, or congenital anomaly of the genitourinary tract) and these patients are most often hospitalized.
Since urine itself is a good culture medium, all specimens should be processed by the laboratory within 2 hours of collection, or be kept refrigerated at 4C until delivery to the laboratory and processed no longer than 18 hours after collection
.
Slide7The examination procedure includes the following steps:
1.
Examination of a Gram-stained smear
. ( for the presence or absence of bacteria,
polymorphonuclear
leukocytes, and
squamous
epithelial cells). One or more bacterial cells per oil-immersion field usually implies that there are 10
5
or more bacteria per milliliter in the specimen. The presence of one or more leukocytes per oil-immersion field is a further indication of UTI
.
2.
A screening test for significant
bacteriuria
. The absence of leukocytes and bacteria in a Gram-stained smear of a clean catch urine sample prepared as described above is good evidence that the urine
is not infected
.
A
urine specimen that is “
negative
” on careful examination of the Gram-stained smear does not need to be cultured.
Slide8An alternative simple and effective
screening test is the test strip for leukocyte esterase/nitrate reduction.
The strip is dipped into the urine specimen as instructed in the package literature.
Any pink
colour
is a positive
reaction indicating the presence of leukocyte esterase and/or bacteria in excess of 10
5
per ml. Urine samples that are positive in the screening test should be cultured as soon as possible to prevent possible overgrowth by no significant bacteria.
If the strip does not develop a
pink
colour
it is interpreted as a negative screening test, is so reported, and no culture is indicated.
3. A definitive culture for urine specimens found to be positive in the screening test.
4.
Susceptibility tests
on clinically significant bacterial isolates should only be performed on well-isolated colonies of similar appearance. Susceptibility tests are generally more important on cultures obtained from patients who are hospitalized or have
a
history of recurring UTI.
Slide9Slide10Procedure of urine culture
The recommended procedure uses a calibrated plastic or metal loop to transfer 1μl of urine to the culture medium.
1. Shake the urine gently, then tip it to a slant and with a 1μl inoculating loop touch the surface so that the urine is sucked up into the loop. Never dip the loop into the urine.
2. Deposit 1μl of the urine on a blood agar plate and streak the plate.
3. Inoculate the
MacConkey
agar in the same manner.
4. Incubate the plates overnight at 35 – 37Cº.
Slide11Culture media for urine culture
The
urine samples routinely culture on conventional media (
Blood agar and
MacConkey
agar
).
Slide12Now urine samples culture
on
CLED
agar (
Cysteine
lactose electrolyte deficient agar):
CLED agar is now used by most laboratories to isolate urinary pathogens
because it gives consistent results and allows the growth of both Gram negative and Gram positive pathogens. It inhibit
Proteus
swarming and accommodate common pathogens
(the indicator in CLED agar is
bromothymol
blue and therefore lactose fermenting colonies appear yellow).
Chromogenic
media
Slide13Slide14Antibiotic susceptibility test
Sensitivity
(susceptibility) testing is used to select effective antimicrobial drugs. The standardized disc-diffusion method (
Kirby–Bauer)
is used.
Disc diffusion techniques are used by most laboratories to test routinely for antimicrobial sensitivity.
A disc of blotting paper is impregnated with a known volume and appropriate concentration of an antimicrobial, and this is placed on a plate of sensitivity testing agar (Mueller–Hinton agar for most bacteria and blood agar for some bacteria) which uniformly inoculated with the test organism.
The antimicrobial diffuses from the disc into the medium and the growth of the test organism is inhibited. Strains sensitive to the antimicrobial are inhibited at a distance from the disc whereas resistant strains have smaller zones of inhibition or grow up to edge of the disc.
Slide15All strains of streptococci should be tested on blood agar for susceptibility.
All Gram-negative rods and staphylococci were tested on Mueller Hinton agar for susceptibility.
Strains of
Hemophilus
and
Neisseria
should be tested for susceptibility using Chocolate agar
.
Slide16Kidney function test
Serum
Creatinine
Creatinine
is a waste product that comes from meat protein in the diet and also comes from the normal wear and tear on muscles of the body.
Creatinine
levels
in the blood can vary, and each laboratory has its own normal range. In many labs the normal range is 0.6 to 1.2 mg/dl. Higher levels may be a sign that the kidneys are not working properly.
As
kidney disease
progresses, the level of
creatinine
in the blood increases
.
Blood Urea Nitrogen
(BUN)
Urea nitrogen is produced from the breakdown of food protein. A normal BUN level is between 7 and 20 mg/dl. As kidney function decreases, the BUN level increases.
Slide17Thank you