Lab diagnosis of diarrhoea
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Lab diagnosis of diarrhoea involves collecting stool or rectal swab samples and transporting them to the lab within 2 hours using Cary Blair medium. Samples are analyzed through microscopy, culture, biochemical tests and serotyping to identify bacteria like E. coli, Salmonella, Staphylococcus aureus, and Vibrio that can cause diarrhoea based on their characteristics like colony morphology, gram staining, motility, and biochemical reactions. Epidemiological typing through bacteriophage is also done to trace the source of infection for some bacteria.
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Lab diagnosis of diarrhoea
- 1. Lab diagnosis of DIARRHOEA Made by – Prashant Arya Roll no. - 74
- 2. Definition of Diarrhoea Diarrhoea is defined as an increase in the frequency, fluidity or volume of bowel movements, relative to the usual habits of an individual. Passage of three or more motions a day can be taken as diarrhoea
- 4. Sample collection I. Stool II. Rectal swab
- 5. Transport Specimens after collection should reach the laboratary with minimum delay(2 hours). The medium used here is CARY BLAIR’S MEDIUM.
- 6. History - History of travel. - History of antibiotics. - Duration of diarrhoea. - History of passage of blood. - History of passage of mucous. - History of rice water stools. - History of food intake. - History of fever
- 7. Sample processing- - Routine/Microscopy -Gross- colour, consistency, blood, mucus, parasite, pH, occult blood Microscopy- Wet mount- saline & iodine. - To look for pus cells/RBC. - To look for ova/cyst/trophozoite. - To look for darting motility (vibrio).
- 8. Culture Pre-enrichment -Blood agar -MacConkey agar -Deoxycholate agar (DCA)/Xylose lysine deoxycholate (XLD) -Thiosulphate citrate-bile-salts agar (TCBS)(if there is history of rice water stool)
- 9. Enrichment media - Selenite F broth - Alkaline peptone water ( if there is history of rice water stool )
- 10. Post-enrichment media - MacConkey agar - DCA/XLD - TCBS (if there is history of rice water stool)
- 11. Colony characteristics :- 1. Staphylococcus aureus – Blood agar- 2-4mm in diameter,circular,raised,opaque Nutrient agar -golden yellow pigment. 2. E.coli – On MacConkey media, colonies are pink due to lactose fermentation. 3. Salmonella – On MacConkey agar &DCA, colonies are colourless due to non-lactose fermentation (NLF). 4. Vibrio – On MacConkey agar , colonies are pale TCBS shows yellow colonies.
- 12. Gram-staining - Staph. aureus-Gram positive cocci arranged in clusters- 1um in diametre , non-sporing. - E. coli-Gram negative bacillus, 1-3um*0.4-0.7um , non-capsulated , non-sporing , - Salmonella-Gram negative bacillus –, 1- 3um*0.5um , non-sporing , non-capsulated. - Vibrio-Gram negative curved/ comma shaped rod , non-sporing , non-capsulated , 1.5um*0.2- 0.4um in size.
- 13. Motility MOTILE – Salmonella , E.coli , vibrio (darting motility). NON-MOTILE – Staphylococcus aureus, Shigella
- 14. Biochemical reactions Indole Urease Citrate VP MR E.Coli + - - - + Salmonella - - +/- - + Staphylococcus aureus- 1. Catalase test – positive 2. Coagulase test (slide & tube) – positive 3. Mannitol fermentation – acid production without gas. Vibrio 1. Catalase – positive 2. Oxidase – positive 3. Indole – positive 4. Reduces nitrates to nitrites 5. Voges–proskauer(VP) – positive
- 15. Serotyping Epidemiological typing Bacteriophage typing - It is done for epidemiological purposes to trace the source infection. It is done in Staphylococcus aureus and Salmonella.