Analysis of summarized data obtained by us on ultrastructure of microbial biofilms of opportunistic bacteria is presented. A complex ultrathin organization of lactobacilli, enterobacteria, staphylococci and enterococci biofilms discovered during electron microscopy is described. The presence of surface film and polysaccharide matrix that determine increased resistance of intrabiofilm bacteria against the effect of protective immune factors of the organism and etiotropic preparations is demonstrated in all the studied comminutes. A varied response of bacterial cells contained in the biofilm during antagonistic effect of symbiont probiotic bacteria was discovered.