The filtration method of air inoculation consists in passing a certain volume of air through a liquid nutrient medium. The simplest is Dyakonov’s method, in which air (10-12 l) is passed through an electric aspirator through a Drexel flask filled with sterile physiological solution. Then, 0.1-1 ml of physiological saline is taken from the flask and inoculated on a Petri dish with a dense nutrient medium. After incubation, the grown colonies are counted and recalculated per 1 m3 of air.
The principle of the shock action of an air jet was realized in the Krotov device (Fig. 20). An electric motor with a centrifugal fan is installed at the base of the cylindrical body of the device, and a rotating disk is placed on the upper part, on which a Petri dish with a dense sterile nutrient medium is mounted. The casing of the device is hermetically closed by a lid with a radially located wedge-shaped slit, through which air aspirated by the fan enters,
a jet of air hits the agar, as a result of which microbial aerosol particles adhere to it. The rotation of the disk with the Petri dish when the device is connected to the network and the wedge-shaped shape of the gap ensure uniform sowing on the surface of the agar. To account for the amount of air passing through the device, a rheometer is installed on its front outer surface, which allows controlling the rate of air aspiration from 20 to 40 liters per minute. Knowing the time (duration) of sampling and the air transmission rate, the amount of aspirated air is determined. At the final stage, the amount of bacterial air pollution is recounted per 1 m3.