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Urinary Tract Infections (UTIs)

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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  1. Urinary Tract Infections (UTIs) Microbiological Investigation 3MED666 Laboratory Investigation of UTIs

  2. 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

  3. Genito-Urinary tract 3MED666 Laboratory Investigation of UTIs

  4. Human kidney 3MED666 Laboratory Investigation of UTIs

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. Antibiotic sensitivities 3MED666 Laboratory Investigation of UTIs

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