2. Other unwanted bacteria are killed, thus allowing the

tubercle bacillus to grow in pure culture.

Petroff’s Method

This is considered to be one of the most reliable methods.

1. Half fill a universal container with the sputum (or other

material) and add an equal quantity of 4% NaOH (For

lesser samples a proportionately equal quantity should

be added).

2. Invert the closed container twice or three times and

place in the incubator for 30 minutes, inverting it every

10 minutes.

3. Centrifuge at 3000 rpm for 30 minutes (The centrifuge

must be completely at a standstill before opening it

again after centrifuging tubercular samples.

4. Discard the supernatant.

5. Add a few drops of neutral red indicator to the deposit.

6. Neutralize with 8% HCl.

7. Inoculate neutralized deposit on the LJ or some other

egg medium.