Comparative growth studies of the lactose and non-lactose fermenting strains of Shigella sonnei.
Lynch, Patricia Mary
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Duval and Schorer (Bact. and Clin. studies from the Rockefeller Inst. for Med. Res., 1904) first isolated the organism now known as Shigella sonnei from cases of infantile diarrhea. Other investigators reported the isolation of organisms closely resembling Duval's bacillus in outbreaks of dysentery. However, it was Sonne (Cent. Bakt. labt. org., 75: 408, 1915) who identified the organism as specific and distinct from the pseudodysentery organisms previously described by Kruse. Thjotta emphasized the variable fermentation of lactose by this organism. Sears and Schoolnik (J. Bact., 31: 309, 1936), Reynolds, etal. (J. Infect. Dis., 55: 207, 1934) and later Cook, Knox and Tomlinson (Brit. J. Exper. Path., 32: 203, 1951) isolated lactose-fermenting (Lac+) mutants from cultures of normal organisms. Kacoyanis (Diserations, Boston University Graduate School, 1955, 1957) found as few as from one to ten Lac+ mutants grew in the presence of large numbers of normal organisms and produced prompt fermentation of lactose and concluded that delayed fermentation of lactose was due to the absence of lactose rather than to the inhibitory action of the normal cells. He stated further that aeration in the presence of lactose favored the appearance of Lac+ mutants. Although Lac+ mutants and normal Sh. sonnei are known to exist, only normal organisms are found in nature. The purpose of the present investigation is to determine the factors that result in the more successful competition or the normal organism in mixed cultures. The comparative growths or the Lac+ mutant and the normal organism were studied by growing them in various liquid media in both pure and mixed culture under aerated and non-aerated (still) conditions. [TRUNCATED]
Thesis (M.A.)--Boston University