[Chromosome markers of drug resistance as the selectors of potential vaccinal strains].

Mutations resulting in acquisition of the resistance to rifampicin, streptomycin, neamine, polymyxin M, mecillinam and high concentrations of nalidixic acid were studied with respect to their effect on virulence of Shigella flexneri by transduction of the markers from the spontaneous avirulent mutants to the initial strain. It was shown that the acquisition of the determinants of the resistance to rifampicin, streptomycin, neamine (nea A) and high concentration of nalidixic acid resulted in 100 per cent of the cases in losing the transductant capacity for causing keratoconjunctivitis in guinea-pigs. With the mutations resulting in the acquisition of resistance to neamine (nea B) and mecillinam virulence was lost only in a part of the clones (33 and 53 per cent respectively). The changes in the pathogenic properties of the transductants with the acquired markers of the resistance to the above antibiotics were associated with impairment of the bacterial cell vital structures. It is suggested that the genetically characterized avirulen immunogenetic mutants be used as potential vaccinal strains.