Living Attenuated Oral Polyvalent Dysentery Vaccine

FORMAL, SAMUEL B. (Walter Reed Army Institute of Research, Washington, D.C.), T. H. KENT, H. C. MAY, A. PALMER, AND E. H. LABREC. Protection of monkeys against experimental challenge with a living attenuated oral polyvalent dysentery vaccine. J. Bacteriol. 91:17-22. 1966.-Virulent strains of Shigella flexneri lb, S. flexneri 3, and S. sonnei I were mated with an Hfr strain of Escherichia coli K-12, and hybrids were selected for the xylose marker. One hybrid strain of each of the serotypes was chosen for study of their biological characteristics. Their capacity to cause a fatal enteric infection in starved guinea pigs was reduced, they failed to cause dysentery when fed to monkeys, they caused keratoconjunctivitis in the guinea pig eye, and they penetrated HeLa cells. Two doses of a polyvalent oral vaccine composed of S. flexneri lb, 2a, and 3, and S. sonnei I hybrid strains were fed to groups of monkeys at an interval of 4 to 7 days, and they, together with controls, were challenged 10 days after the last dose with one or another of the virulent parent dysentery strains. A significant degree of protection was afforded in all vaccinated groups with the exception of one group challenged with S. flexneri 6, a component not included in the vaccine. When animals were challenged with virulent S. flexneri 2a 1 month after oral vaccination, they were also protected. The vaccine produced a rise in serum antibody, but we were not able to detect coproantibody in saline extracts of feces from animals which received the vaccine. We previously have shown that a strain of Shigella flexneri 2a lost its capacity to cause a fatal enteric infection in starved guinea pigs when, by recombination, it incorporated into its genome the genetic material between the rhamnose-xylose region of an Hfr strain of Escherichia coli (1). Such a hybrid strain retained its ability to invade tissue, but appeared to be unable to multiply in the intestinal mucosa (2). A single oral dose of 5 X 1010 cells of the hybrid strain sufficed to render monkeys resistant to experimental oral challenge with the virulent parent strain of S. flexneri 2a (3). There are over 30 different serotypes of dysentery bacilli, and it is not at all certain whether hybrid strains of others would possess properties similar to those of our S. flexneri 2a hybrid strain. The purpose of this communication is to describe the characteristics of hybrid strains of S. flexneri lb, S. flexneri 3, and S. sonnei I, and to present the results of studies in which a livng polyvalent oral vaccine was used to protect monkeys against experimental challenge. MATERIALS AND METHODS Cultures. S. flexneri lb strain 1Z, S. flexneri 2a strain 2457T, S. flexneri 3 strain J17B, S. flexneri 6 strain CCH060, and S. sonnei I strain 53G were all isolated from human beings with bacillary dysentery. Escherichia coli Hfr strain W1895 and E. coli-S. flexneri 2a hybrid strain X16 have been described previously (2, 3; Formal et al., in press). Mating procedures. The methods used to obtain E. coli-Shigella hybrid strains were similar to those already described (1, 2). Biological tests. Tests for the ability of the various strains to invade HeLa cells, to produce keratoconjunctivitis, to fatally infect guinea pigs, to multiply in the small intestine of the starved guinea pig, to cause dysentery in monkeys, and to protect monkeys against experimental challenge have been described previously (2, 3, 4). Serological tests. The passive hemagglutination test was used to detect serum and coproantibody 17 on A uust 0, 2017 by gest http/jb.asm .rg/ D ow nladed fom