Index Organism for Pasteurization
The index organism for pasteurization is:
- Coxiella burnetti — Correct Answer
- Mycobacterium tuberculosis
- Leptospira
- Listeria
Correct Answer: Coxiella burnetti
Coxiella burnetti is the index organism for pasteurization. It is the causative agent of Q-fever and is the most heat-resistant pathogen that is destroyed by pasteurization. If pasteurization conditions (72°C/15 sec for HTST) are adequate to destroy C. burnetti, all other milk-borne pathogens are also destroyed.
Key Features of Coxiella burnetti
- Causes Q-fever (Query fever) in humans — an occupational hazard for farmers, abattoir workers, and veterinarians.
- It is an obligate intracellular parasite (rickettsial organism).
- It forms spore-like structures making it heat-resistant.
- Transmitted via raw milk, aerosols, and contact with infected animal products.
Why the Phosphatase Test is Used
Phosphatase enzyme is naturally present in raw milk and is completely destroyed at pasteurization temperatures. So phosphatase test of pasteurized milk should be negative — a positive result means pasteurization was inadequate.
Why Other Options Are Wrong
- Mycobacterium tuberculosis → causes bovine TB (milk-borne disease), but is less heat-resistant than C. burnetti.
- Leptospira → causes Leptospirosis; also milk-borne but less heat-resistant.
- Listeria → causes Listeriosis; important food safety pathogen but not the index organism for pasteurization.
📚 About this Topic — Animal Refresher
This multiple choice question is from Animal Refresher, Dairy Science. It has 4 options with a detailed explanation of the correct answer. Practice more MCQs from Animal Refresher to strengthen your preparation.
