INFLUENCE OF THE HEATING AT 120°C ON BACTERIAL CELLS

PART I. MAINLY ON VI ANTIGEN

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Vi antigen fails to agglutinate when heated at 60°C for 1 hour, thus, it has been considered that the antigen is destroyed by heating.
Stuart and Kennedy stated, in 1948, that upon heating a bacterial suspension, nearly all of the Vi antigen contained is separated from the bacterial cells and the supernatant fluid obtained after its centrifugation has an inhibitory effect on Vi agglutination because the removed free Vi antigen absorbs Vi antibody prior to cause agglutination reaction.
At the Group Meeting sponsored by the National Institute of Health and the Institute for Infectious Diseases held on May 1951, this author reported that the reason why Vi antigen, when heated, fails to agglutinate, is not because it is destroyed but due to its swift isolation into the medium in a large quantity in proportion to the temperature of heating. For instance, when a bacterial suspension heated at 56°C for 1 hour is used in the agglutination test, the reaction is positive at lower dilutions of the Vi serum where there is an abundant amount of Vi antibody, while it is negative at higher dilutions where there is only but a small amount of the antibody. As the bacterial suspension is in a constant concentration, probably, all the Vi antibody contained in the higher dilutions of serum is absorbed by the free Vi antigen in the suspension, whereas, at lower dilutions, there may still some amount of antibody left over to cause the agglutination. Accordingly, when the agglutination is made either with the bacterial suspension removed of free Vi antigen by centrifugation or with the suspension prepared from the culture grown at 22°C inhibiting the development of Vi antigen, it is practicable to cause the agglutination with extremely high serum dilutions.
No appreciable difference was observable, upon running Vi precipitation tests, between the heating at 56°C for 1 hour and at 100°C for 2 hours. Thus, saline suspensions of typhoid bacilli V form were heated at varying temperatures of 56°C, 100°C and 120°C for 1 hour and Vi precipitation tests were made with the supernatant fluids obtained by their centrifugation. Precipitin titers of the supernatant fluids subjected to different temperatures of heating were practically equal, whereas, upon running Vi agglutination tests with the bacterial precipitates of the above suspensions, a strange phenomenon was observed which was the precipitate of the suspension heated at 120°C showed slight agglutination.