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					Chapter 37 – Urinary
Tract Infections


MLAB 2434 – Clinical Microbiology
Keri Brophy-Martinez
Definitions
   UTI = Urinary Tract Infection
      Spectrum of diseases caused by microbial invasion
       of the genitourinary tract
   Upper UT includes renal parenchyma (pyelonephritis)
    and ureters (ureteritis)
      Symptoms include: fever, flank pain& tenderness
   Lower UT includes bladder (cystitis), urethra
    (urethritis), and, in males, the prostrate (prostatitis)
        Symptoms include: pain on urination, increased
         frequency, urgency, suprapubic tenderness
   Bacteriuria = presence of bacteria in urine; may be
    symptomatic or asymptomatic
Urinary System
   Except for urethral mucosa and renal
    medulla, the urinary tract efficiently and
    rapidly eliminates microorganisms
   Conditions such as high ammonia
    concentration, hyperosmolarity, lowered
    pH, and sluggish blood flow in renal
    medulla can contribute to reduced
    leukocyte chemotaxis and bactericidal
    activity of WBCs
   Normal flora of Urinary tract p. 1017
    Table 37-3
Risk Factors

   Age
       Infants to Pre-school age
         • Girls infected more than boys
         • Most renal damage due to UTI at this age
       School-age children
         • Presence of bacteria in urine defines population
           at higher risk for development of UTIs in
           adulthood
         • Girls more prone to develop UTI upon sexual
           activity
Risk Factors (cont’d)

   Age (cont’d)
       Adults to 65
        • UTIs in men extremely low, except with
          anatomic abnormalities or prostate
          disease or as a result of
          instrumentation ( catheterization)
        • 20% of women in this age group
          experience symptomatic UTI
Risk Factors (cont’d)

   Age (cont’d)
       Over age 65 and residence in long-term
        care facility
         • UTIs increase dramatically in both genders
         • Atypical clinical presentation: fever, delirium,
           failure to thrive
         • Males – prostate changes and increased
           catherization, neuromuscular disease
         • Women – fecal soiling, neuromuscular disease,
           bladder prolapse and increased catheterization
Risk Factors (cont’d)

   Inpatient Care
     Hospitals and nursing homes
     More prone to UTIs due to
      pathologic conditions and higher
      probability of urinary tract
      instrumentation
Clinical Signs and
Symptoms
   Infants and children < 2 years age have
    nonspecific symptoms( failure to thrive,
    vomiting, lethargy, fever)
   > 2 years are more likely to have localized
    symptoms (dysuria, frequency, abdominal
    or flank pain)
   Adults with lower UT infections have
    dysuria, frequency, urgency, and
    sometimes suprapubic tenderness
Clinical Signs and
Symptoms (cont’d)
   Upper UTIs, especially with acute
    pyelonephritis, include LUTI symptoms
    along with flank pain and tenderness and
    fever
   AGN (Acute Glomerulonephritis) – results
    from immune response to S. pyogenes
    (Group A) infections, either respiratory
    or pyodermal
       Edema around eyes
       Hematuria
       RBC and WBC casts
Etiology of UTIs

   Pathogenesis of UTI
       Three access routes
         • Ascending (most significant)
              • Usually seen in females since ureter is shorter
         • Descending
              • Also referred to as Hematogenous/Blood-borne
              • Occurs as a result of bacteremia
              • Less than 5% of UTI’s
         • Lymphatic
              • Increased pressure on bladder causes a redirect of
                lymph fluid to kidney
              • Infection dependent on size of the bacteria, strength
                of the bacteria present, and how strong the body's
                defense mechanisms are at the time.
              • Very rare
UTI Agents
   G- Bacilli
      E. coli (most common due to fecal
        contamination)
       Pseudomonas, Proteus, Klebsiella, &
        Enterobacter sp. ( increased frequency
        due to catheters and hospitalization)
   G+ Cocci
      Enterococcus – more commonly in older
        men, due to catheters or prostrate
        hypertrophy
       S. saprophyticus – sexually active young
        women
UTI Agents (cont’d)

   G+ Bacilli
      Bacillus is a contaminant
      Others (Mycobacterium, Listeria,
       Clostridium)
   Fungi ( Candida)
   Some powerful STIs will produce UTIs
    (Ex. N. gonorrhoeae, C. trachomatis,
    Gardenella vaginalis)
   Viruses ( Herpes, Adenovirus)
   Anaerobes
Specimen Collection

   Need to collect specimen to prevent
    normal vaginal, perianal, and urethral
    flora
   Mid-stream clean catch – if self
    collected, patient needs GOOD
    instructions
   Catheterized- sample must come from
    port NOT bag
   Suprapubic aspiration ( only for anaerobic
    culture)
Specimen Collection (cont’d)

   Additives – even with additive, time from collection
    to processing should not exceed 24 hours
      Grey top culture tubes( sodium borate) keep
       sample integrity for up to 48 hours
   Dip-slide urine collection – better for physician
    offices
   Transport
      If not processed or preserved, urine should be
       cultured within 2 hours
      If refrigerated, urine can be held for 24 hours
Specimen Screening

   Manual screening
       5 to 10 WBC/hpf is upper limit of normal
       Chemical screening
         • Leukocyte Esterase and Nitrate on urine
           dipstick
   Automated methods – expensive, except
    in large volume labs
   Gram stains generally not performed on
    urines
Causes for Rejection

   Inadequate method of collection or transport
   Labeling incomplete ( name, source, acc #
    etc.)
   Insufficient volume
   Fecal contamination
   24 hour urines and Foley catheter tips must
    be rejected for culture
Culture and Interpretation
   Inoculation using either a 0.001ml(x1000) OR a
    0.01 ml (x100) loop onto selective/nonselective
    media, such as BAP and MAC
   Dip calibrated loop into well-mixed urine. Quickly
    make a single streak down the middle of the BAP
    with the loop containing urine
   Streak back and forth across the plate
    perpendicular to the original inoculum, this creates
    a “lawn”
   With the same calibrated loop, do the same with
    the MAC plate
   Incubate at 35oC for 24-48 hours
Culture and Interpretation
Culture and Interpretation

   Interpretation of urine cultures is
    determined by medical staff of hospital
       Is there growth?
         • If no growth:
            • At 24 hours:
                • Preliminary report: no growth at 24 hours
                • Reincubate plates
            • At 48 hours:
                • Final report: no growth at 48 hours
                • Discard plates
Culture and Interpretation

   If there is growth, what media has
    it grown on?
     BAP only: rules out the enteric
      GNR’s, colonies may be GPC, GPR,
      GNDC
     BAP and MAC: most likely an enteric
      GNR or Pseudomonas. If multiple
      colony types, a gram stain must be
      done.
Culture and Interpretation
(cont’d)
   How many colony types are growing?
       Specimen with ≥ three organisms is
        probably contamination and should not be
        identified unless specifically requested by
        physician
       One or two pathogens ≥ 100,000 CFU/ml
        should be identified and sensitivities done
       One or two pathogens ≥ 100 CFU/ml should
        be identified only if clinical situation
        warrants or specimen is catheterized or
        suprapubic aspiration
Culture and Interpretation
(cont’d)
   Things to consider in UTI’s
     Colony count of pure or predominant
      organism
     Measurement of pyuria
     Presence or absence of symptoms

				
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