Pasteurization target organism: The HTST condition of 71.1°C for 15 seconds (high-temperature short-time) is established primarily on the heat resistance of which organism?

Introduction / Context:
Milk pasteurization time–temperature combinations are chosen to inactivate the most heat-resistant non-spore-forming pathogen reasonably expected in milk. This ensures safety while preserving quality.

Given Data / Assumptions:

• HTST: 71.1°C for 15 s (also written 72°C for 15 s in many jurisdictions).
• Target is the most heat-resistant vegetative pathogen in raw milk.
• Spore-formers are not completely inactivated by pasteurization.

Concept / Approach:
Coxiella burnetii (agent of Q fever) exhibits relatively high thermal resistance among vegetative pathogens found in milk. Designing the HTST process against C. burnetii ensures a wide margin against other vegetative pathogens such as Listeria, Salmonella, and pathogenic E. coli, which are less heat resistant at these conditions.

Step-by-Step Solution:
Identify the heat-resistance benchmark organism for milk. Differentiate vegetative cells from spores (e.g., Bacillus, Clostridium). Confirm that pasteurization aims at vegetative pathogens, not spores. Select Coxiella burnetii as the basis.

Verification / Alternative check:
Thermal death data show D-values for C. burnetii higher than other common milkborne vegetative pathogens, supporting its use as the design target.

Why Other Options Are Wrong:
E. coli and Listeria are less heat resistant; Bacillus/Clostridium spores survive pasteurization and require sterilization for destruction.

Common Pitfalls:
Assuming pasteurization equals sterilization; shelf-stable UHT uses higher temperatures specifically to inactivate spores.

Final Answer:
Coxiella burnetii.