Enrichment of spore-formers: For selecting endospore-forming bacteria from a mixed culture, at what temperature–time treatment is the culture commonly heated to eliminate vegetative cells while preserving spores?

Introduction / Context:
Endospore-forming genera such as Bacillus and Clostridium produce highly resistant spores. Heat treatment is a classic enrichment technique to select these organisms by killing heat-sensitive vegetative cells.

Given Data / Assumptions:

• Goal: enrich for spore-formers from a mixed culture.
• Endospores tolerate higher temperatures than vegetative bacteria.
• Short exposure is used to minimize spore damage while eliminating competitors.

Concept / Approach:

Thermal shock at about 80°C for around 10 minutes is widely used to destroy non-spore-forming vegetative cells, leaving endospores viable. After cooling, the sample is plated on appropriate media and incubated, allowing spores to germinate and grow into colonies.

Step-by-Step Solution:

Verification / Alternative check:

Protocols in teaching labs and clinical references consistently cite 80°C/10 min as an effective spore enrichment step; lower temperatures may be insufficient, and much higher or longer treatments may reduce spore viability.

Why Other Options Are Wrong:

70°C or 60°C for 10 minutes: often inadequate to remove all vegetative competitors.

90°C for 10 minutes: risks damaging spore viability in many species.

Common Pitfalls:

Overheating or prolonged exposure; failing to cool before plating; assuming all colonies after heat shock are spore-formers without confirmatory tests.

Final Answer:

80°C for 10 minutes