Question

In Eijkmans test, inoculum from positive PCT tubes is transferred to MacConkey's broth tubes and incubated at ________.

• A. 44.5 $\pm$ 0.2$^\circ$C for 24 $\pm$ 2h
• B. 42.0 $\pm$ 0.5$^\circ$C for 24 $\pm$ 2h
• C. 44.5 $\pm$ 0.2$^\circ$C for 48 $\pm$ 2h
• D. 42.0 $\pm$ 0.2$^\circ$C for 48 $\pm$ 2h

Hint:

Remember the diagnostic temperature for fecal coliforms:
- Standard coliforms = $37^\circ\text{C}$.
- Fecal coliforms (E. coli) = $44.5^\circ\text{C}$ in a water bath.
The temperature must be controlled precisely within $\pm 0.2^\circ\text{C}$.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The Eijkman test is a classic bacteriological assay used to differentiate fecal coliforms (primarily Escherichia coli) from non-fecal coliforms.
The test relies on the ability of fecal coliforms to ferment lactose and produce gas at elevated temperatures that inhibit other organisms.
Detailed Explanation:
The test is conducted as part of a multi-step analysis:
1. Presumptive Coliform Test (PCT): Milk or water samples are incubated in MacConkey broth at $37^\circ\text{C}$ to detect lactose fermentation.
2. Eijkman Test (Confirmatory Test): Inoculum from the positive, gas-producing PCT tubes is transferred to fresh MacConkey's broth (or EC medium) containing Durham tubes.
These tubes are incubated in a highly accurate, temperature-regulated water bath at $44.5 \pm 0.2^\circ\text{C}$ for $24 \pm 2\text{ hours}$.
At this elevated temperature ($44.5^\circ\text{C}$), the growth of non-fecal coliforms (such as Enterobacter aerogenes) is suppressed.
Only fecal coliforms can grow and ferment lactose to produce gas within 24 hours.
If gas production is observed in the Durham tube within 24 hours, the test is positive, indicating fecal contamination.
If no gas is produced, the sample is negative for fecal coliforms.

Step 2: Final Answer:
The incubation conditions are $44.5 \pm 0.2^\circ\text{C}$ for $24 \pm 2$ hours.