Urinary tract infections utis
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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)

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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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