(PMBO11)

(2023- 2024)

Yomna Hashem, PhD

Department of Microbiology
Faculty of Pharmacy, The British
University, Egypt
 Diagnosis of Urinary Tract Infections

• A urinary tract infection, or UTI, is an infection in any part of the urinary system,
which includes kidneys, bladder, ureters, and urethra.

• Urinary tract infections (UTIs) are characterized as being either upper or lower.

• Upper UTIs involve the kidney (pyelonephritis) or the ureters (ureteritis).

• Lower UTIs involve the bladder

(cystitis), the urethra (urethritis), and in
males, the prostate (prostatitis).
UTIs can be classified as:
1- Single versus recurrent episode
A single-episode UTI occurs once while recurrent or chronic UTIs have repeated
episodes of bacteriuria (the presence of detectable bacteria in the urine), with or
without clinical manifestations.

2- Complicated versus uncomplicated episode

• Uncomplicated infections occur primarily in healthy females and

occasionally in male infants and adolescent and adult males. Most
uncomplicated infections respond readily to antibiotic agents to which the
etiologic agent is susceptible.

• Complicated infections occur in both sexes in patients with structural or

functional abnormalities of the urinary tract, patients with indwelling urinary
catheters, or have certain diseases like diabetes. In general, complicated
infections are more difficult to treat and have greater morbidity (e.g., kidney
damage, bacteremia) and mortality compared with uncomplicated infections
Risk Factors for UTIs

1- Female sex

• UTIs occur more frequently in women than men, Why?

➢ Because the female urethra is relatively short compared with the male urethra and
lies near the perirectal region, so bacteria can reach the bladder more easily in
the female host.

2- Age
• Children: UTI in children is associated with great morbidity and long-term
medical problems, including impaired renal function, hypertension, and end-
stage renal disease.

• In patients older than 65 years: neuromuscular disease and increased

instrumentation and bladder catheterization are contributing factors. For
men, the enlargement of the prostate interferes with the emptying of the
bladder.
UTI is a common cause of bacteremia in older adults.
3- Institutionalized Care

• Hospitalized patients and those residing in long-term care facilities develop UTIs
more often compared with outpatients. The generally ill condition of the
hospitalized population, higher probability of urinary tract instrumentation, and
higher incidence of GU tract anatomic or functional abnormalities are major
contributors to this difference.

4- Pregnancy

• Hormonal changes lead to changes in the ureter and urethra, making them more
susceptible to bacterial adherence and infection. In addition, the enlarging uterus
can put pressure on the bladder and impair urinary flow, leading to cystitis or
pyelonephritis.

• pregnant women should be treated because infection can lead to premature labor
as well as infectious complications in the fetus or the newborn.

• Susceptibility testing is particularly important because not all antibiotics can be

given to pregnant women.
5- Bladder Catheterization

• UTIs are the most common hospital-acquired infections, accounting for

approximately one-third of health care–associated infections. Up to 95% are related
to bladder catheterization and/or manipulation.

• In a catheterized patient, the risk of acquiring a UTI depends on the duration of

catheterization, appropriate catheter care, and host susceptibility.

6- Diabetes mellitus

• Diabetes can increase the risk of UTIs because it damages the nerves that
control the bladder.

7- Kidney stones

• Kidney stones can block the flow of urine, which can increase the risk of UTIs.

8- Structural or functional abnormalities of the urinary tract

9- Renal Transplantation
Causes of Urinary Tract Infections
• Bacteria may gain access to the urinary tract by three routes: (1) The
ascending route, (2) the hematogenous route, and (3) lymphatic pathways.

Ascending route

• the major mechanism for the development of UTI

• Ascending route is the most common course of infection in females,

• Ascending route associated with instrumentation is the most common cause

of hospital-acquired UTIs.

• For UTIs to occur by the ascending pathway, enteric gram-negative bacteria

and other microorganisms that originate in the gastrointestinal tract must be
able to colonize the vaginal cavity or the periurethral area. Once these
organisms gain access to the bladder, they may multiply and then pass up the
ureters to the kidneys.
Hematogenous route

• The hematogenous spread usually occurs as a result of bacteremia.

• Any systemic infection can lead to seeding of the kidney, but certain organisms,
such as Staphylococcus aureus or Salmonella spp., are particularly invasive.

Lymphatic pathways

• Increased pressure on the bladder can cause lymphatic flow into the kidneys,
resulting in UTI.
Causative Agents
• Escherichia coli is the most frequent cause of uncomplicated community-
acquired UTIs.

• In more complicated UTIs, particularly in recurrent infections, the relative

frequency of infection caused by Proteus, Pseudomonas, Klebsiella, and
Enterobacter spp. increases.

• Hospitalized patients are most likely to be infected by E. coli, Klebsiella spp.,

Proteus spp., staphylococci, Pseudomonas aeruginosa, enterococci, and
Candida spp.
Signs & Symptoms

• UTIs symptoms in children younger than 2 years are usually nonspecific, such
as failure to thrive, vomiting, lethargy, and fever.

• Children older than 2 years are more likely to complain of more localized
symptoms, such as dysuria, frequency, and abdominal pain.

• Adults with lower UTIs limited to the urethra or bladder present primarily with
dysuria, often in combination with frequency, urgency, suprapubic pain, and
hematuria.

• Patients with upper UTIs, such as pyelonephritis, present with flank pain,
nausea, vomiting, fevers, chills, night sweats, and costovertebral angle
tenderness.

• Dysuria and frequency may precede the onset of upper urinary tract and
systemic symptoms by 1 or 2 days.

• Bacteremia, when present, may help confirm a diagnosis of pyelonephritis.

• Symptoms of UTI can differ widely.

• Cases of pyelonephritis may be asymptomatic, and manifest symptoms such as

those of lower UTIs, or present as life-threatening sepsis.

• Most older patients have atypical presentations, such as delirium, failure to

thrive, and/or weakness.

• Although dysuria is the most common reason for obtaining a urine culture
specimen, this clinical presentation is neither sensitive nor specific, Why?

Dysuria may be present in infections with herpes simplex virus,

Chlamydia trachomatis, or Neisseria gonorrhoeae. These organisms
are not detected by the routine bacteriologic culture of urine. Many
noninfectious conditions, including urethral inflammation from
physical or chemical agents or because of trauma, may have similar
symptoms.
Laboratory Diagnosis

Specimen Collection

Clean-catch, midstream specimen:

• Guidelines for proper specimen collection should be printed on the container

and the procedures clearly described to help ensure patient compliance.

• The patient should be instructed to clean the periurethral area well with a mild
detergent to avoid contamination.

• Of importance, the patient should also be instructed to rinse well because the
detergent may be bacteriostatic.

• After cleaning the patient collects a midstream urine sample.

Catheterized Specimen Collection

• Catheterized specimen collection, an invasive technique, reduces the risk of

contamination of urine by the urethral flora; however because the catheter is
passed through the urethra, some contamination may occur.

• Before urine is collected with a single straight catheter, the urethral opening
or vaginal vault is cleansed

• The initial urine flow is discarded because it may contain organisms acquired
as the catheter passes through the urethra.

• When specimens are collected from an existing, indwelling urinary catheter,

the catheter collection port should be cleaned with an alcohol pad and
punctured directly with a needle and syringe.

• The specimen should never be collected from the drainage bag.

Suprapubic Aspiration

• Suprapubic aspiration is the definitive method for collecting uncontaminated

specimens.

• Although most consider any organism isolated from these specimens to be

clinically significant, this may not be correct because transient colonization of
the bladder can occur.

• Suprapubic aspirations are collected primarily from infants and from patients
in whom the interpretation of the results of voided specimens is difficult for
various reasons.

• Suprapubic aspiration of urine specimens is the only suitable method to

obtain an anaerobic culture.

• Following skin antisepsis, urine is collected from a full bladder by using a

needle and a syringe
Specimen Transport

• Urine is an excellent supportive medium for the growth of most

uropathogens, so it must be immediately refrigerated or preserved.

• Generally, urine should be refrigerated, received, and processed in the

laboratory within 2 hours of being collected.

• Bacterial counts in refrigerated (4°C) urine remain constant for as long as

24 hours.

• Longer delays render examination for significant pyuria unreliable, and the
extremes of pH and urea concentration and the presence of antimicrobial
agents may adversely affect the recovery of uropathogens.
Microbial Detection

Specimen Screening: Rapid Nonculture Methods

• As many as 60% to 80% of all urine specimens received for culture may
contain no etiologic agents of infection or contain only contaminants,
procedures were developed to identify quickly those urine specimens

• A reliable screening test for the presence or absence of bacteriuria provides

physicians with important same-day information that a conventional urine
culture may take a day or longer to provide.

• Many screening methods have been advocated for use in detecting bacteriuria
and/or pyuria. These include microscopic methods, enzymatic methods,
photometric detection of growth, etc
Microscopy

➢ Detection of Bacteria When Pyelonephritis Is Suspected

• Gram staining of urine samples should be performed because it may reveal the
causative agent.

• Uncentrifuged urine samples may be used for a stained smear.

• The presence of one or more bacterial cells per oil immersion field in at least five
fields in a smear of uncentrifuged urine correlates with more than 105 CFU/mL.

• The presence of gram-positive or gram-negative bacteria or fungi assists in

selecting an appropriate antibiotic therapy.

➢ Detection of Pyuria
• Pyuria often indicates urethritis, cystitis, or pyelonephritis.

• Detection of leukocytes may be performed by microscopic examination of a wet

mount of urinary sediment resulting from centrifugation

• A hemocytometer chamber can be used to examine fresh uncentrifuged

specimens.
Indirect Indices

Frequently, screening tests detect bacteriuria or pyuria by examining for the presence
of bacterial enzymes or PMN enzymes rather than the organisms or PMNs
themselves.

Nitrate Reductase (Griess) Test.

This screening procedure looks for the presence of urinary nitrite, an indicator of
UTI. Nitrate-reducing enzymes that are produced by the most common urinary
tract pathogens reduce nitrate to nitrite. This test also tests for leukocyte
esterase, an enzyme produced by PMNs.

Catalase

Test for the presence of catalase enzyme present in most bacterial species
commonly causing UTIs except for streptococci and enterococci.
Hydrogen peroxide is added to the urine, and the solution is mixed gently. The
formation of bubbles above the liquid surface is interpreted as a positive test.
Automated Urine Screening Methods

• Bioluminescence:

• Colorimetric Particle Filtration

➢ Such systems may be expensive, may frequently require batching of

specimens (therefore time delays), and have not been adequately
evaluated for their efficacy in detecting low-grade bacteriuria and
funguria.
Urine culture

• Urine culture should include plating onto one gram-negative selective medium
(MacConkey or eosin–methylene blue) and one nonselective medium (blood agar).

• A selective plate for gram-positive organisms, such as Columbia colistin-nalidixic

acid agar (CNA) due to heavy growth of Enterobacteriaceae that mask gram-
positive growth can be used.

• Chromogenic agar can be useful to

identify and distinguish organisms in
mixed cultures.

• Before inoculation, urine should be

mixed thoroughly, and the sample
should be taken by calibrated loop.
Interpretation of Results

• UTIs may be completely asymptomatic, produce mild symptoms, or cause

life-threatening infections. Of importance, the criteria most useful for
microbiologic assessment of urine specimens is dependent not only on the
type of urine submitted (e.g., voided, straight catheterization) but the clinical
history of the patient (e.g., age, sex, symptoms, antibiotic therapy).

• One major problem in interpreting urine cultures arises because urine cultures
collected by the voided technique may be contaminated with normal flora,
including Enterobacteriaceae. Determining what colony count represents true
infection from contamination is of utmost importance and is related to the
patient’s clinical presentation.
Treatment

• All forms of symptomatic bacterial urinary tract infection (UTI) require antibiotics.
For patients with troublesome dysuria
Thank you