Infectious diseases caused by conditionally pathogenic bacteria, special forms of microbial communities are forming bacterial biofilms that can screen the surface of the mucous membranes of the gastrointestinal tract. Bio- films, due to special protective structures, microbial cells can synthesize biologically active substances and show increased resistance to the effects of humoral factors of the protection of the macroorganism and antimicrobial agents. In connection with the search for new therapeutic and prophylactic drugs with the ability to effectively inhibit the development of bacterial biofilms of opportunistic pathogens, but without damaging the structure of normal microbiocenosis, an electron microscopic study was conducted and the inhibitory properties of chitosan on biofilms of opportunistic bacteria S. aureus 6 and P. indica 3.