The in vivo and in vitro interactions between tomato (Lycopersicon esculentum Mill.) and tobacco (Nicotiana tabacum L.) and the bacteria Pseudomonas fluorescens, Acinetobacter baumannii, Rhodococcus erythropolis,Pseudomonas aureofaciens, Pseudomonas putida, Methylovorus mays have been studied. These microorganisms were shown to be in stable associations with plants. The colonized plants were characterized by more rapid growth, a higher yield, and better adaptation to in vivo conditions. The colonized plants were more resistant to bacterial phytopathogens Erwinia carotovora and Pseudomonas syringae. Plants colonized by naphthalene-resistant bacteria can grow steadily on a medium containing this compound. The results demonstrate the prospects of the use of beneficial associative microorganisms in the development of technologies for plant protection against biotic and abiotic stressors.