A Microbiology topic on Urinary Tract Infection, covering various subtopics like the causative organism, clinical features and more importantly, the lab diagnosis.
Reference: Textbook of Medical Microbiology, Ananthnarayan & Paniker
9. Lab Diagnosis
• Collection and transport of specimen
• Microscopy
• Screening
• Culture
• Antibiotic Sensitivity Test
10. Collection of Specimen
Collection
Midstream urine
Male
Female
Catheter sample
urine
During cystoscopy
Early morning
Urine
TB of urinary
tract
Suprapubic
Aspirate
Children, infant
and older women
Initial Flow
Urethritis,
Prostatitis
11. Transport of Specimen
• At room temp - half an hour
• Refrigerated at 4⁰- 4 hrs
• Not processed beyond this time
• No immediate access – Spl. container
with 1.8% boric acid
• Contamination-False +ve
12. Microscopy
• Urine centrifuged and deposit
examined under microscope
• The following can be seen:
• Pus cells ( > 5/hpf)
• Bacteria
• Epithelial cells
• RBC
13. Culture:
• Semi-quantitative cultures
• Standard loop technique
• Involves a ‘standard calibrated loop’ –
transfers fixed, small quantity of urine
• Culture Media:
• Mac Conkey Agar
• Blood Agar
• Mac Conkey- quantitative measurement
• Blood- presumptive diagnosis
14. • Colony count of 105/ml – Significant
• 104/ml – 105/ml – Doubtful significance
• < 104/ml – Significant only if:
• On prior antibiotics
• Obstruction in UT
• Fungal infection/pyelonephritis
• Specimen is suprapubic aspiration
• ≥ 3 types of organism - Contaminants
Fixed and small amount
of uncentrifuged urine
is transferred to
BLOOD and
MacCONKEY AGAR
Incubate at 37⁰ C for
24 hours
Next day, the number
of colonies grown is
counted and total count
per ml is calculated
15. Screening
• Necessity:
• UTI is a common problem
and facilities are not always
available
• Used for presumptive
diagnosis
Catalase
Test
Griess
Nitrite
Test
TTC
(Triphenyltet
razolium
chloride)
Gram Stain
Dip Slide
Culture
Glucose
Paper Test
16. 1. Griess Nitrite Test:
• Normal urine does not contain nitrite
• Is based on nitrate reducing enzyme produced by bacteria
during infection
2. Catalase Test
• Certain bacteria have catalase enzyme which acts on
hydrogen peroxide to release oxygen
• +ve rection evident by formation of
bubble
• Only in catalase +ve organism
17. 3. Triphenyl tetrazolium chloride:
• Is based on production of pink red precipitate in the reagent
• Caused by respiratory activity of growing bacteria
4. Gram stain:
• Microscopic demonstration of bacteria in gram stained
films of urine
18. 3. Glucose Paper Test:
• Is based on utilization of minute amount
of glucose in the normal urine utilized by
the bacteria causing infection
4. Dip Slide Culture:
• CLED agar on one side and MacConkey on another coated
slide → immersed in urine → incubated at 37⁰C → growth
estimated by colony counting or color change
19. Antibiotic Sensitivity:
• E. coli and other urinary pathogens –
multi drug resistance; transferable
variety
• Necessary to administer proper
antibiotics
• Primary susceptibility test with urine
specimen is done
• Confirmed by AST using bacteria
recovered in culture