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I am writing my lab record fill these according to answers from apurba Shastri

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Apurba Shastri microbiology cholera Vibrio cholerae diagnosis treatment lab record

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I now have all the information needed. Here are the complete answers for your lab record, based on Apurba Shastri (Sastry)'s Microbiology:

Exercise 12.A - Lab Record Answers

Clinical case: 40-year-old patient with frequent passage of watery stools with flecks of mucus, nausea, vomiting, and severe dehydration.

1. Probable Clinical Diagnosis and Causative Agent

Clinical Diagnosis: Cholera (Acute secretory diarrhea)
Causative Agent: Vibrio cholerae - a Gram-negative, comma-shaped (curved) bacillus belonging to the family Vibrionaceae. The serogroup responsible for epidemic/pandemic cholera is V. cholerae O1 (or O139). It produces cholera toxin (CT) which causes profuse watery ("rice-water") diarrhea through activation of adenylate cyclase, leading to massive fluid and electrolyte loss and severe dehydration.

2. Simple and Quick Preliminary Diagnostic Test

Hanging drop preparation / Dark-field microscopy
A fresh stool sample is placed as a hanging drop and examined under dark-field (or phase contrast) microscopy. Vibrio cholerae shows characteristic rapid "darting" or "shooting star" motility. A presumptive diagnosis can be established within minutes:
  • Motility is observed as rapid, darting movement
  • When a drop of polyvalent anti-cholera diagnostic serum is added, motility ceases (immobilization test) - this confirms the organisms are cholera vibrios
This test gives a presumptive diagnosis in ~80% of cases within a few minutes.

3. Observations of Tests Displayed and Interpretation

TestObservationInterpretation
Hanging drop / Dark-field microscopyRapidly motile, comma-shaped bacilli with darting ("shooting star") movement; motility inhibited by polyvalent anti-cholera serumPresumptive Vibrio cholerae
Gram stainingGram-negative, curved/comma-shaped bacilliConsistent with Vibrio cholerae
Culture on TCBS agar (Thiosulphate Citrate Bile Salt Sucrose agar)Large, smooth, yellow colonies (sucrose fermenters)Characteristic of V. cholerae
Alkaline peptone water (enrichment)Turbid surface pellicle after 4-6 hours at 37°CEnrichment of V. cholerae (grows well in alkaline media)
Oxidase testPositive (oxidase positive)Consistent with Vibrio species
String testPositive - organisms form a mucoid string when a colony is touched with a loopConfirmatory for V. cholerae
Interpretation: The clinical features (rice-water stools, severe dehydration, vomiting) combined with microbiological findings confirm Cholera caused by Vibrio cholerae.

4. Sample Collection, Transportation, and Alternative Options (Patient 20 km from Lab)

Appropriate Sample: Fresh diarrheal stool (rice-water stool)
Standard Collection:
  • Collect fresh stool by rectal swab or rubber catheter (No. 26-28 French) into transport medium
  • Transport medium: Alkaline peptone water (APW) or Venkatraman-Ramakrishnan (VR) medium or Cary-Blair medium
  • Transport in sterile McCartney bottles (30 ml) within 2 hours
Alternative Options for Remote/Field Settings (20 km away):
  1. Rectal swab in Cary-Blair transport medium - Cotton-tipped swab soaked in liquid stool, placed in Cary-Blair medium; this maintains viability for up to 48 hours during transport
  2. Alkaline peptone water (APW) transport - Soak swab in stool and place in APW (pH 8.6); V. cholerae thrives in alkaline pH
  3. If no transport medium available: Soak cotton swab in liquid stool, place in a sterile sealed plastic bag and send immediately to the lab by the quickest available transport
  4. Bedside culture: If bile salt agar plates are available, streak the stool directly at bedside and send the plates along with transport medium
  5. Blotting paper/filter paper method: Stool-soaked filter paper strips can be dried and sent - viable for isolating V. cholerae even after drying

5. Treatment in Order of Preference

  1. Oral Rehydration Therapy (ORT) - First and foremost priority
    • WHO-ORS (Oral Rehydration Salts): Na+ 75 mmol/L, K+ 20 mmol/L, Cl- 65 mmol/L, glucose 75 mmol/L, citrate 10 mmol/L
    • Rice-based ORS is superior to standard ORS in cholera
    • Continue until diarrhea stops
  2. IV Fluid Replacement (for severe dehydration / unable to tolerate oral fluids)
    • Ringer's Lactate (preferred) or Normal Saline
    • Given rapidly in cases of severe dehydration, vomiting, or altered sensorium
  3. Antibiotics (after vomiting has subsided, usually after 3-4 hours of rehydration)
    • 1st choice: Doxycycline - single dose 300 mg (adults) - drug of choice
    • 2nd choice: Azithromycin - 1g single dose (preferred in pregnant women and children)
    • 3rd choice: Ciprofloxacin / Fluoroquinolones
    • 4th choice: Tetracycline - 500 mg 4 times daily for 3 days
    • Alternative: Co-trimoxazole (TMP-SMX) or Ampicillin
Note: Antidiarrheals, antiemetics, antispasmodics, and corticosteroids are NOT to be given.

6. Other Possible Pathogens Responsible for Diarrhoea

Bacterial:
  • Escherichia coli (ETEC, EPEC, EHEC, EIEC, EAEC)
  • Shigella spp. (bacillary dysentery)
  • Salmonella typhi / non-typhoidal Salmonella
  • Campylobacter jejuni
  • Yersinia enterocolitica
  • Clostridium difficile (antibiotic-associated diarrhea)
  • Staphylococcus aureus (food poisoning)
  • Bacillus cereus
  • Clostridium perfringens
Viral:
  • Rotavirus (most common cause of diarrhea in children)
  • Norovirus (Norwalk virus)
  • Adenovirus (enteric)
  • Astrovirus
Protozoal/Parasitic:
  • Entamoeba histolytica (amoebic dysentery)
  • Giardia lamblia (giardiasis)
  • Cryptosporidium parvum
  • Cyclospora cayetanensis
  • Isospora belli
These answers are based on Apurba Shastri (Sastry)'s Microbiology textbook approach, cross-referenced with Park's Preventive Medicine and standard microbiology references. Write them in your own handwriting as appropriate for your lab record format.
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