Question

The method suited for enumerating the presence of low numbers of microorganisms in food is

• A. MPN method
• B. Spread plate method
• C. Pour plate method
• D. Dye reduction method

Hint:

Microbiological Enumeration: Low Bacterial Densities Coliforms ($< 10 - 30\text{/g}$) $\rightarrow$ MPN (Most Probable Number) Method. Moderate to High Counts $\rightarrow$ Pour Plate Spread Plate.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Statistical food microbiology: the Most Probable Number (MPN) multiple-tube fermentation technique provides high sensitivity for enumerating very dilute microbial concentrations ($< 10-30 ext{ cells/g}$) below standard agar plate counting limits.
Key Formula or Approach:
\[ \text{Limit of Detection: Agar Plates (Pour/Spread) } \approx 30 - 300\text{ cfu/g} \quad \longleftrightarrow \quad \mathbf{MPN \text{ Method }} < \mathbf{3 - 10 \text{ organisms/g}} \]

Step 2: Detailed Explanation:
Comparison of quantitative enumeration methods in food and water microbiology:
1. Most Probable Number (MPN) Method (A): A statistical multi-tube liquid dilution assay based on Poisson probability distributions. It is the preferred and standard method for estimating low numbers of microorganisms (such as coliforms, E. coli, Vibrio, Clostridium) in foods, seafood, and shellfish waters when the population density is too dilute ($< 10 - 30\text{ organisms/g}$) to be accurately detected or counted on solid agar plates.
2. Pour Plate Spread Plate Methods: Reliable only for higher bacterial counts within the countable range of $30 - 300\text{ colonies/plate}$.

Step 3: Final Answer:
Therefore, the method suited for low numbers is MPN method, matching option (A).