Bacterial contamination is quite frequent in plant tissue cultures although, theoretically, cultures have to be axenic. It is their ubiquity and adaptability to different conditions that enable bacteria to colonize also tissue cultures. Among them there are not only the typical endo- and egzophytic species connected with the plant kingdom, but also those which are common among people. The bacteria species isolated from plant tissue cultures were found to be vitropathogenic (pathogens facultative to in vitro explants), latent (pathogens not virulent in vitro), and cryptic (present in tissues but invisible). Some bacteria produce growth regulators, which can modify the morphogenetic mode of explants. They are all undesirable ones in cultures, but the explants contaminated with pathogenic species should be eliminated obligatorily. Various groups of bacteria, as well as the techniques of detecting, identifying and eliminating them, are briefly described.