[Role of multiple drug resistance in the biology of pathogenic and opportunistic bacteria].

The significance of cloning of pathogenic and opportunistic multiple drug-resistant bacteria is analysed from the present viewpoints of medicine and veterinary. Distribution of drug-resistant strains in men, animals and environment and occurrence of new type hospital and nosocomial infections are described. The controversial points of the antibiotics role in the formation of multiple drug resistance plasmids, occurrence of hospital resistant strains and the part of R plasmids in changing the biological characteristics of pathogenic and opportunistic bacteria are analysed. It is shown in relation to Salmonella that formation of definite clones of multiple drug resistant bacteria results in significant changing of epidemiology of the diseases caused by these organisms. The data on the identity of the biological and genetic characteristics of the Salmonella strains of some phage vars isolated in hospitals and outside the hospitals, as well as the data on the effect of R plasmids on the Salmonella virulence are presented. The thesis of a higher infective capacity of the strains with multiple drug resistance associated with their increased survival levels and a higher colonization ability is accentuated. The danger of occurrence of new type causative agents on formation of complex plasmids with additional determinants connected with the bacteria pathogenicity is discussed. The tasks of the further investigation of these aspects are formulated and the possible means for the control of this phenomenon are presented.