xmlns:atom="http://www.w3.org/2005/Atom"
52. After counting the colonies, characteristic colonies shall be taken at random from the agar plates, the number being at least the square root of the colonies counted. Each of the colonies shall be subcultured onto a nutrient agar plate and incubated aerobically at 37°C ± 1°C for 20 hours ± 2 hours.