Enumeration of microorganisms in foods: What does the term “enumeration” refer to in standard food microbiology plate-count methods?

Introduction / Context:
Enumeration yields quantitative results (CFU/g or CFU/ml). Different plating techniques are chosen based on expected counts, matrix type, and whether selectivity is required to suppress background flora.

Given Data / Assumptions:

• Validated techniques include pour plate, spread plate, and spiral plating.
• Medium choice (selective vs non-selective) depends on the analyte (e.g., total aerobic count vs coliforms).
• Serial dilutions and replicates improve accuracy.

Concept / Approach:
For total aerobic counts, non-selective media (e.g., Plate Count Agar) are used. For target groups (e.g., coliforms, Staphylococcus aureus), selective/differential media are applied. Spiral plating automates precise deposition for high-throughput enumeration with reduced agar usage.

Step-by-Step Solution:
Define enumeration as CFU-based quantitation via culture. List core plating methods used to enumerate. Tie medium selectivity to test purpose. Select the comprehensive option reflecting both method and media choice.

Verification / Alternative check:
Regulatory compendia describe acceptable variants for enumeration with equivalent performance criteria (countable range, incubation conditions).

Why Other Options Are Wrong:
Selective-only or non-selective-only definitions are too narrow; microscopy without culture is not standard “enumeration” in this context.

Common Pitfalls:
Counting plates outside 25–250 CFU range; inaccurate dilutions compromise results.

Final Answer:
Spiral plating, pour plate, or spread plate of a food suspension onto a suitable selective or non-selective agar, depending on the test objective.