Postgate’s assay technique is useful for determining whether a cell is viable even when it is in which state?

Introduction / Context:
Viability does not always equal active division. Some cells persist in a non-dividing or “resting” state yet remain alive and potentially resuscitable. Postgate’s assay (historically used with difficult anaerobes such as sulfate-reducing bacteria) helps detect life in such states.

Given Data / Assumptions:

• Target cells may be metabolically active but non-culturable by routine plating.
• Specialized conditions and indicators are used to reveal metabolic activity.
• Cell division may be absent during the test period.

Concept / Approach:
The principle is to provide a conducive, often reduced environment with suitable electron donors/acceptors and sensitive readouts (for example, color changes, sulfide formation) that report metabolism. A positive signal indicates viability despite failure to form colonies, distinguishing truly dead cells from temporarily non-dividing ones.

Step-by-Step Solution:
Recognize the scenario: cells are alive but not dividing. Use an assay that detects metabolic activity rather than colony formation. Interpret positive metabolic signals as evidence of viability. Select the option that states “incapable of cell division.”

Verification / Alternative check:
Similar logic underpins viability dyes (e.g., esterase substrates) and resuscitation media that detect life in viable-but-non-culturable (VBNC) states.

Why Other Options Are Wrong:

• Too small to see: Size does not determine assay choice.
• Obligate aerobe/Thermophile: Growth requirements, not the key issue addressed by Postgate’s viability detection.

Common Pitfalls:
Equating “no colonies” with “no viability.” Some organisms require specialized conditions or time to resume division.

Final Answer:
incapable of cell division.