Laboratory diagnosis of urinary tract infection

Lab diagnosis of UTI
1. Defination
2. Etiopathogenesis
3. Specimen Collection
4. Microscopy
5. Culture
6. Biochemical Tests
7. Screening

1. Lab Diagnosis OF UTI Department of microbiology Group D

2. OUTLINE Definition Eitopathogenesis Specimen collection Microscopy Culture Biochemical tests Screening

3. Urinary Tract Infection UTI is an infection in any part of the urinary system , mainly associated with dysuria , frequent urination , flank pain and burning sensation while urination.

4. Etiology Gram – ve bacilli : E.coli , Klebsiella , Proteus Gram + ve bacilli : Staphylococcus , Enterococci Miscellaneous : M. tuberculosis , Citrobacter Fungus : Candida albicans Virus : Adenovirus , Herpes simplex Parasites: Schistosoma hematobium

5. Causative Agents of UTI

6. Predisposing Factors Stasis of urine Sexually active males and females Pregnancy Poor aseptic catheterization Instrumentation Stones Mothers with bacteriuria during pregnancy

7. Pathogenesis Bacterial adhesion Activation of Cytokines Production of Adhesins Chemotaxis of leukocytes

8. Laboratory Diagnosis Specimen Collection : Collected prior to antibiotics Specimen is collected in a sterile container Early morning sample is to be collected Mid Stream Specimen

9. Females Males Clean the area with soap and water , hold the labia apart and discard few ml of urine and then collect the midstream sample directly into the sterile container Clean the glans with soap and water, retract the foreskin , dicard few ml of urine and then collect the mid stream sample directly into the sterile container The first portion of urine adquately flushes out the normal urethral flora

10. Catheter Specimen Urine should be collected directly from the catheter and not from the collection bag Catheterization to obtain urine is not done because of risk of introducing infection though it yields excellent result.

11. Supra Pubic Aspiration Ideal method for collection from infants

12. Transport Tests should be carried out immediately , if delay is unavoidable then the specimen can be refrigerated for up to four hours at 4˚C Boric acid , glycerol , sodium formate can be used as preservative.

13. Microscopy Urine is centrifuged and deposit is examined under microscopy. Following can be observed : Pus cells (normal: 0-5 / HPF ) RBC Epithelial cells Bacteria Gram’s Staining is performed.

14. Culture- Differential MacConkey ’s Agar : Differential media to differentiate lactose fermenter ( E.coli and klebsiella ) CLED Media : Selective media for E.coli Blood Agar: Non-selective media

15. Standard Loop Technique Most used method Involves a standard calibrated loop which transfers a fixed and small volume of urine.

16. Interpretation of Result Bacteriological diagnosis is done by Kass Criteria: Significant Bacteriuria (>10 5 /ml ) : Active UTI Doubtful Bacteriuria (10 4 to 10 5 /ml): Culture should be repeated. Non-significant Bacteriuria (<10 3 /ml): the sample is considered as contaminated with genital commensals.

17. Dip Slides Commercially available plastic slides coated with CLED agar on one side and MacConkey’s agar on the other is dipped in urine and placed in sterile container and incubated at 37ºC.

18. Pour Plate Method Quantitative method Not used for routine diagnostic tests

19. Biochemical Reactions Species Indole Methyl Red Voges-Proskauer Citrate utilization Escherichia coli + + - - Proteus + + - - Klebsilella pneumoniae - - + + Citrobacter koseri + + - +

20. Griess Nitrite Test Based on nitrate reducing enzymes produced by bacteria present in urine Gram – ve bacteria: Nitrates >> Nitrites Normal urine does not contain nitrite The presence of nitrite indicated UTI

21. Triphenyltetrazolium Chloride Test TTC is reduced by several frequently encountered urinary tract pathogens and produce pink red precipitates This reaction only happens in or near living cells that release hydrogen as they respire.

22. Antibiotic Sensitivity Test TTC is reduced by several frequently encountered urinary tract pathogens and produce pink red precipitates This reaction only happens in or near living cells that release hydrogen as they respire.

23. References

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