Question

In assessing hygienic quality of khoa pan, a 100 cm2 area of the pan was swabbed into 25 ml of rinse solution and 1 ml of 10^-1 dilution of the rinse solution was plated out in duplicate. After incubation, 15 and 25 colonies were observed on the plates. What is the hygienic quality of the khoa pan?

• A. Good
• B. Satisfactory
• C. Unsatisfactory
• D. Fairly satisfactory

Hint:

Swab Rinse Hygiene Calculation: $\text{Density} = \frac{\text{Colonies} \times \text{Dilution Factor} \times \text{Rinse Volume}}{\text{Swabbed Area}} = \frac{20 \times 10 \times 25}{100} = 50\text{ cfu/cm}^2$ $\rightarrow$ SATISFACTORY ($< 100\text{ cfu/cm}^2$).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Surface sanitation hygiene evaluation: swab rinse method calculations determining bacterial colony forming units per square centimeter ($ ext{cfu/cm}^2$) and standard equipment sanitation sanitary grade thresholds.
Key Formula or Approach:
\[ \text{Colonies/Plate (Average)} = \frac{15 + 25}{2} = 20 \]
\[ \text{Total CFU in Rinse (25 mL)} = 20 \times \frac{1}{10^{-1}} \times 25\text{ mL} = 20 \times 10 \times 25 = 5,000\text{ CFU} \]
\[ \text{CFU per } \text{cm}^2 = \frac{5,000\text{ CFU}}{100\text{ cm}^2} = \mathbf{50 \text{ cfu/cm}^2} \quad [\text{Standard Sanitary Limit: Satisfactory}] \]

Step 2: Detailed Explanation:
Step-by-step mathematical calculation of surface swab hygienic quality:
1. Average Colony Count on Duplicate Plates:
\[ \bar{N} = \frac{15 + 25}{2} = 20\text{ colonies/plate} \]
2. Bacterial Concentration in Dilution ($10^{-1}$):
\[ \text{Concentration in Rinse} = \frac{20\text{ cfu}}{1\text{ mL} \times 10^{-1}} = 200\text{ cfu/mL} \]
3. Total Bacterial Load on Swabbed Area (25 mL Rinse):
\[ \text{Total Load} = 200\text{ cfu/mL} \times 25\text{ mL} = 5,000\text{ cfu} \]
4. Bacterial Density per Unit Surface Area ($100\text{ cm}^2$):
\[ \text{Bacterial Density} = \frac{5,000\text{ cfu}}{100\text{ cm}^2} = \mathbf{50\text{ cfu/cm}^2} \]
5. Sanitary Hygiene Grading (Standard Public Health Swab Standards):
- Good (Excellent): $< 10\text{ cfu/cm}^2$
- Satisfactory (B): $10\text{ to 50\text{ cfu/cm}^2$ (or $< 100\text{ cfu/cm}^2$)}.
- Unsatisfactory: $> 100\text{ cfu/cm}^2$.
- Therefore, the calculated hygienic quality of the khoa pan is Satisfactory.

Step 3: Final Answer:
Hence, the hygienic quality of the khoa pan is Satisfactory, corresponding to option (B).