The principle of this method is
that a developed TLC plate is dipped in a suspension of microorganisms growing in a proper broth and then incubated in a humid
atmosphere. A silica surface of the TLC plate covered with the
broth medium becomes a source of nutrients and enables growth
of the microorganisms directly on it. However, in the places
where antimicrobial agents were spotted, the inhibition zones
of the microorganism growth are formed. Visualization of these
zones is usually carried out using dehydrogenase activity-detecting reagents; the most common are tetrazolium salts. The dehydrogenase of living microorganisms converts tetrazolium salt into
intensely colored formazan. As a result, cream-white spots appear
against a purple background on the TLC plate surface, pointing the
presence of antibacterial agents.