By using the method which has been developed for isolation and studying of microorganism strains, associative to particular plant species, the strain Pseudomonas fluorescens P10 has been isolated and its features of colonization of cabbage plant organs has been studied. In this study, different colonizing abilities of the strain are shown depending on the site of its isolation during germination and development of plants from inoculated seeds Brassica capitata var. alba Lizg. The ability of the strain to exist in epiphytic and endophytic forms and interaction with cabbage plants has been determined. It has been shown that this method can be used for strain activation during passage through plants.