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Urinary Tract Infections (UTIs). Microbiological Investigation. 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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urinary tract infections utis

Urinary Tract Infections (UTIs)

Microbiological Investigation

3MED666 Laboratory Investigation of UTIs

predisposing factors
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

3MED666 Laboratory Investigation of UTIs

genito urinary tract
Genito-Urinary tract

3MED666 Laboratory Investigation of UTIs

human kidney
Human kidney

3MED666 Laboratory Investigation of UTIs

types of uti
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

3MED666 Laboratory Investigation of UTIs

causative agents mainly faecal bacteria
COMMUNITY -ACQUIRED

Escherichia coli

Proteus mirabilis

Klebsiella pneumoniae

Enterococcus faecalis

Staphylococcus species

HOSPITAL –ACQUIRED

Pseudomonas aeruginosa

Candida albicans

AND (community acquired)Mycobacterium tuberculosis (renal TB – will be a ‘sterile pyuria’

Causative agents: mainly faecal bacteria

3MED666 Laboratory Investigation of UTIs

investigation the specimen
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!!

3MED666 Laboratory Investigation of UTIs

standard procedures
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

3MED666 Laboratory Investigation of UTIs

microscopy
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

3MED666 Laboratory Investigation of UTIs

white cells in urine
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 >200/μl (>200 x 103/ml) and will suggest this as significant pyuria
  • Lower numbers: < 103/ml are regarded as not significant

3MED666 Laboratory Investigation of UTIs

automation
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
  • For example, flow cytometry

3MED666 Laboratory Investigation of UTIs

culture procedure
Culture: procedure
  • Cystitis is usually caused by a single species of bacterium present at >105/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 >100 colonies; this = >100 bacteria/μl or >105/ml

3MED666 Laboratory Investigation of UTIs

culture interpretation
Culture: interpretation
  • >105/ml of a single species strongly suggests a UTI
  • 104-105/ml of a single species is equivocal – needs repeat specimen for testing
  • <104/ml is regarded as no significant growth
  • >1 species in any numbers suggests contamination
  • Catheter and suprapubic urines should be interpreted differently

3MED666 Laboratory Investigation of UTIs

sensitivity testing
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

3MED666 Laboratory Investigation of UTIs

antibiotic sensitivities
Antibiotic sensitivities

3MED666 Laboratory Investigation of UTIs

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