URINARY TRACT INFECTIONS
Dr.T.V.Rao MD
Over view of Urinary Tract
Infections
Most common infectious disease
Most Numerous specimens are received in the
Laboratory
30 to 40 % of specimens received in Microbiology
laboratories are Urine specimens, to Identify the
Infection.
Diagnostic information is important for the clinician.
Appropriate clinical information gives many
clues for better diagnostic evaluations.
Specimen collection is the primary objective in getting an
ideal sample.
Why women are at More Risk for
Urinary Tract Infections
Women tend to have
urinary tract infections
more often than men
do because the
urethra is shorter in
women than in men,
so bacteria have a
shorter distance to
travel.
Who are at Risk with UTI
Urinary tract infection is much more
common in adults than in children, but
about 1-2% of children do get urinary tract
infections. Urinary tract infections in
children are more likely to be serious than
those in adults and should not be ignored.
Most Important facts to establish
Infection
Simple microscopic examination of wet
films of unconcentrated urine for detection
of Polymorphonuclear leucocytes - pus
cells gives leading clues
Semiquantitative culture of urine to
detemine wether urine contain
potentially pathogenic bacteria in
Numbers sufficent to identify it as
causative agent causing infection.
Common Presenting Symptoms
Urgency
Frequency of
Micturation
Discomfort and pain
in abodemen or on
passing urine
Organs Involved in UTI
The following organs are
infected
Kidney
Bladder
Ureters
Donot include Urethra,
Infections of Urethra is
called as Urethritis, dealt
under different clinical
syndromes
Common site and Microbes
Patients in majority of
cases present with
infection of Urinary
Bladder and called
as Cystitis
Most common
pathogen is
Escherichia coli.
Common Path og ens c au sing
UT I
Staphylococcus
saprophyticus
Klebsiella pneumonia
– var aerogenes or
oxytoca
Proteus mirabilus,
other coliforms
Pseudomonas
aeruginosa
Streptococcus faecalis
Candida being a
fungus can cause
Rare Microbes causing UTI
Streptococcus
agalactiae
Streptococcus milleri
Other Streptococci
Anaerobic
Streptococci
Gardernella vaginalis
Serious Infections associated with UTI
Acute pyelitis
Pyelonephritis
May lead to Bacterimias detected by
Blood culture
A prominent infection with
Staphylococcus aureus can cause
above manifestions.
UTI without Routine Bacterial
isolates
Some times it puzzles the clinicians, patients
present with symptoms of urinary tract infection
but bacteria donot grow on Routine culture
Media
May be associated with
Organisms that donot grow on selected
media
Can be a Genito urinary tract Tuberculosis
Gonococcal infections
Nationally exacting or anaerobic bacteria
Non B ac te ri al Ureth ritis,Cys ti ti s
an d Ureth ral s ynd ro mes
One should be
familiar with
Urethral or Bladder
infections with
Chlamydia
Ureaplasma
Trichomonas
Viral infections
Simple tests to rule out Urinary
tract infections
In les equipped
laboratories routine
testing for detection of
Nitrite
Blood
Protein
By rapid automated
dipsticks can give basic
information
But eliminates about ½
of culture negative
specimens.
Collecting Urine for examination
Collect the Mid
stream specimens of
Urine
Donot collect
spontaneously
collected urine
without instructions,
which can lead to
contamination with
commensals bacteria
Specimen Collection
The urine collected in a
wide mouthed container
from patients
A mid stream specimen is
the most ideal for
processing
Female patients passes
urine with a labia
separated and mid
stream sample is
collected
Specimen collected in young and
Children
Non invasive methods are safe
and ideal
Follow the Broomhall et al
method
By tapping just above the pubis
with two fingers place on
suprapubic region after 1 hour
of feed, tapping on at the rate
of 1 tap/second for aperiod of
1 minute, if not succesul
tapping is repated once agin.
The child spontaneously pass the
Urine and to be collected in a
sterile container
Transport of Urine for Culturing
Urine
All collected specimens of
urine to be transported to
laboratory with out delay
Delay of 1 – 2 hour deter
the quality of diagnostic
evaluations.
If the delay is anticipated
the specimens are at
preserved at 40c
In field conditions Boric
acid can be added at a
concentration of 1.8 %
Proof of Urinary Tract Infection
Needs presence of potential pathogens in
the freshly voided urine or scientifically
preserved specimens in numbers greater
than those likely to result from
contamination from urethral meatus and
the surrounding,
Kass suggested the Number to be about
105 or more ( 1,00,000 / ml of urine )
Diagnosis of Urinary Tract
Infection
Step 1
Microscopy of
Urine for detection of
Pyuria.
Leucocytes should
be found in numbers
of at least as great as
104 / ml before the
pyuria is established
Wet Film examination of Urine
All wet films to be examined
with high power ( x 40 )
objective.
Prepare the drop of urine after
mixing the urine without
centrifugation
Transfer 0.05 ml on the middle
of the microscope slide and
cover slip is applied.
The prepared specimen show
a small excess of fluid along
the edges of the cover slip.
A approximate finding of 1
leukocyte / 7 high power fields
corresponds to presence of
pyuria.
Cu lturi ng of u ri ne for Isol ati on
of B ac teri al patho gens
Semiquantitative
culture
Select the Media
For common isolates
Mac Conkey’s agar
helps in differentation
of Lactose fermenting
organisms from non
lactose fermenting
pathogens
Selection of Loop for
Semiquantitative Method
Culture Media for isolations-
CLED Medium
It is also an excellent
universal culture medium
owing to its wide spectrum
of nutrients, lack of
inhibitors and the fact that it
allows a certain degree or
differentiation between the
colonies. It contains lactose
as a reactive compound
which, when degraded to
acid, causes bromothymol
blue to change its colour to
yellow. Alkalinization
produces a deep blue
colouration. The lack of
electrolytes suppresses the
swarming of Proteus
Culture Media for Isolation
Blood agar
helps in isolation of
fastidious, extracting
strains
May extended incubation
for isolation of pathogens
for more than 48 hours
with added atmosphere of
5 – 10 % co2
Specimen Inoculations
All cultures processed by
Semiquantitative method a
loop of standard dimension of
approximately known volume
is inoculated into selected
culture plate
In general a loop of SWG – 28
with a diameter of 3.26 mm
internal diameter which can
hold a drop of water or urine
0.004 ml.
After inoculation the culture
plates are incubated at 370c
extending to > 18 hours are
read
The colony counts are made,
as each colony corropsdes to
number of viable bacteria per
ml of urine
Reading the Culture Plates
A true infection in the absence of prior antibiotic therpay the number
of bacteria is likely to be at least 105 or more.
Contaminated specimens present with colony counts <104, however
even less than 103
On several occasions the colonies are diverse species
Several studies prove counts >104 to be considered as presence of
Urinary tract infection with the supporting clinical history
On some occasions more than one pathogen is isolated but should
be processed for all practical purposes
eg E.coli along with Streptococcus fecalis
On few occasions even counts 103 are
proved significant
Identification of Gram +
organisms
All colonies identified
morphologically as
Staphylococcus to be
characterized as
Staphylococcus aureus
Staphylococcus
saprophyticus
Staphylococcus
epidermidis
Enterococci - fecal group of
organisms
Identification of Isolates
Gram + isolates
The minimal tests to
differentiate Gram +
cocci include
1 Catalase
2 Coagulase test
3 Bile esculin testing
4 Bacitricin in
Streptococcus isolates
Biochemical tests in Gram -
bacilli
Catalase test
Oxidase test
Nitrite reduction test
Indole test
Methyl red test
V P test
Citrate test
Decarboxylation tests
Lysine, ornithine, Arginine
tests
Mac Conkey’s agar showing
Proteus and E.coli
Blood agar showing
Coagulase negative
Staphylococcus
Most important
Yet many theories on Significant bactenuria are
contraversioal.
The reporting of results should be maninly based on
clinical history.
Even a true infection may contain only 103
In such circumstances tests to be reported as probably
or possibly significant
A good coordination between a Microbiologist and
Physcian is the best solution associated with best
solutions to patients with Urinary tract infections.
Reporting of Contaminated
specimens
Microscopy helps to detect pus cells and
epithelial cells, an insignificant grwoth with
few pus cells can ignored as contaminants
In females even the presence of
leucocytes with Squamous epthelial cells
without a defined significatn growth should
be ignored.
Antibiotic Sensitivity
Always use a pure
grwoth of the isolates.
Perform testing for
antibiotic sensitivity
with inoculam which
is comparable to
defined Macfarland
standards.
Most serious Infections
presenting as Urinary tract
Infections
Acute pyelitis
Pyelonephritis
May present with loin
pain, fever,
Apart from Urine culture
patients present with
Bacteriaemia - can be
detected by Blood
culture.
Causative agent can be
Staphylococcu aureus
Clinical Problems
manifesting as Urinary
tract Infections
An infection of the
Genitourinary tract
where the Microbes
donot grow on
selected media as in
Mycobacterium
tuberculosis
Gonococcus
Nutritionally exacting
or anaerobic bacteria
Non Specific Urethritis
Several conditions mimic
Urinary tract infection which
are associated with organism
other than routinely isolated in
simple and few selective
media, they can be
Can be urethral or Bladder
infections with
Chlamydia
Ureplasma
Trichomonas,
Few viruses
Deal ing wi th UTI
The chemotherapy of proven infection
may guided by in vitrosensitivity tests on
the pathogen isolated by culture and
outcome of therpay assessed by
examination of urine at the conclusion of
treatment.
Follow up examination of patients with UTI
is important, if neglected can lead to
chronic and permanent complications.
Antibiotic Sensitivity Testing
All the isolated
bacteria identified as
pathogenic to be
tested for Antibiotic
Sensitivity/Resistance
pattern by disk
diffusion methods
Antibiotic Sensitivity
Always use a pure
grwoth of the isolate.
Perform testing for
antibiotic sensitivity
with inoculam which
is comparable to
defined Macfarland
standards
Rationalsim of Antibiotic
Selection
If the patient is attending a
General practice, outpatient
clinic, drugs suitable by oral
administration should be
selected
The discks are with defined
content to test the pathogens
in the urine
Amoxycillin or Ampicillin 25
Cephelexin 30 µg
Nalidixic acid 30µg
Ciprofloxacin 5µg
Nitrofurantoin 50µg
Trimethoprim 2.5
ß Lactamase producing Gram
negative strains
There is a grwoing incidence of ßlactamase producing strains in
particular associated with Hospital acquired infections
The newly defined methods to be used as per the NCCL
guidelines.
There is a growing need for testing for
Amikacin,
Netilmicin,
Tobramycin
Netilmicin
Ticarcillin
There is a grwoing list organisms associated
with Hospital Infections need better
identification testing with new generation of
drugs.
Created as Teaching Module for
Medical Students in Devloping
world
Dr.T.V.Rao MD
Email
doctortvrao@gmail.com
