Chapter 37 Urinary Tract Infections

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Chapter 37 Urinary Tract Infections

• MLAB 2434 Clinical Microbiology
• Keri Brophy-Martinez

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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

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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

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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

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Risk Factors (contd)

• Age (contd)
• 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

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Risk Factors (contd)

• Age (contd)
• 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

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Risk Factors (contd)

• Inpatient Care
• Hospitals and nursing homes
• More prone to UTIs due to pathologic conditions
  and higher probability of urinary tract
  instrumentation

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Clinical Signs and Symptoms

• Infants and children lt 2 years age have
  nonspecific symptoms( failure to thrive,
  vomiting, lethargy, fever)
• gt 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

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Clinical Signs and Symptoms (contd)

• 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

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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 UTIs
• 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

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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

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UTI Agents (contd)

• 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

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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)

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Specimen Collection (contd)

• 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

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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

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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

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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

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Culture and Interpretation
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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

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Culture and Interpretation

• If there is growth, what media has it grown on?
• BAP only rules out the enteric GNRs, 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.

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Culture and Interpretation (contd)

• 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

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Culture and Interpretation (contd)

• Things to consider in UTIs
• Colony count of pure or predominant organism
• Measurement of pyuria
• Presence or absence of symptoms