Urinary Tract Infections UTIs

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Urinary Tract Infections (UTIs)

• Microbiological Investigation

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Predisposing factors

• Sexual activity in females
• Elderly males prostatic hypertrophy
• Young children with inherited defect, e.g.
  vesico-uretic reflux
• Pregnancy
• Catheterisation
• Surgery, e.g. prostatectomy
• Diabetes mellitus

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Genito-Urinary tract
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Human kidney
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Types of UTI

• Non- sexually transmitted!
• Cystitis inflammation of bladder wall
  accompanied by dysuria and frequency
• Cystitis is much the commonest, discomforting but
  not serious
• Upper tract infections, e.g. pyelonephritis, are
  much more serious
• Accompanied by fever and risk of complications

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Causative agents mainly faecal bacteria

• COMMUNITY -ACQUIRED
• Escherichia coli
• Proteus mirabilis
• Klebsiella pneumoniae
• Enterococcus faecalis
• Staphylococcus species

• HOSPITAL ACQUIRED
• Pseudomonas aeruginosa
• Candida albicans
• ANDMycobacterium tuberculosis (renal TB will
  be a sterile pyuria

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Investigation the specimen

• Mid-stream Urine (MSU) is the specimen of choice
• Suprapubic urine
• Catheter urine
• In all cases, urine must be examined immediately
  or stored at 4oC
• Contamination of urine is a big problem!!

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Standard procedures

• Investigation of UTI involves the detection of
  bacteriuria together with evidence of an
  inflammatory response
• Microscopy for pyuria and haematuria (can also
  reveal other structures, e.g. crystals, other
  cells, casts
• Culture for detection of bacteria
• Sensitivity testing to advise on antibiotic
  treatment

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Microscopy

• Not always performed as it is time consuming
• The finding of a rise in WBCs (pyuria) should be
  linked to a bacteriuria
• May also see RBCs (haematuria) this is
  potentially an important finding
• Microtitre plate and an inverted microscope
  enables many urines to be simply screened

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Automation

• Looking for particles suspended in a fluid
• In the same way platelets and white cells can be
  automatically estimated in blood, so, too, can
  urine be analysed for its cellular content
• Faster, less labour intensive and reliable

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White cells in urine

• In normal state, there is a continuous secretion
  of WBCs into urine
• In a UTI caused by bacteria, neutrophils may be
  secreted in large numbers
• Labs may report gt200/µl (gt200 x 103/ml) and will
  suggest this as significant pyuria
• Lower numbers lt 103/ml are regarded as not
  significant

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Culture procedure

• Cystitis is usually caused by a single species of
  bacterium present at gt105/ml
• Standard loopful of urine is streaked onto a
  selective medium, e.g. CLED
• Typically 1µl
• Incubate overnight and count the colonies
• If a genuine UTI, should see gt100 colonies this
  gt100 bacteria/µl or gt105/ml

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Culture interpretation

• gt105/ml of a single species strongly suggests a
  UTI
• 104-105/ml of a single species is equivocal
  needs repeat specimen for testing
• lt104/ml is regarded as no significant growth
• gt1 species in any numbers suggests contamination
• Catheter and suprapubic urines should be
  interpreted differently

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Sensitivity testing

• Clinical isolates are tested against antibiotics
  that a) are filtered by kidneys and b) are
  usually effective against common agents
• Since UTIs are common, drugs should be cheap!
• Typical course of treatment 5-7 days orally,
  resulting in sterile urine
• Nitrofurantoin, nalidixic acid, trimethoprim,
  ampicillin gentamicin, cephalosporins

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Antibiotic sensitivities