Antagonism between Virulent and Avirulent Shigella or Escherichia coli
1981 Volume 55 Issue 6 Pages 400-409
Details
1981 Volume 55 Issue 6 Pages 400-409
Experiments on antagonism between virulent and avirulent strains were carried out, using Shigella flexneri 2b 17-A (Sh. flex. 2b 17-A, a virulent strain), Shigella flexneri 2b 17-N (Sh., flex. 2b 17-N, an avirulent strain), Escherichia coli 0-124 (E. coli 0-124S, a virulent strain) and R form Escherichia coli 0-124 (E. coli 0-124R, an avirulent strain). The results of the experiments may be summarized as follows:
1) Cultured on Congo red agar, Sh. flex. 2b 17-A and E. coli 0-124R were differentiated from Sh. flex. 2b 17-N and E. coli 0-124S; that is, the former absorbed Congo red dye, showing red colony (CR+ colony) and the latter did not absorb the dye, showing colorless colony (CR colony).
2) There is no significant difference in the growth ability of these strains in the broth at 37°C. The generation time of them was about 25 minutes. On the mixed cultivation of the virulent and the avirulent strains in the broth, these strains were found to be almost equal in number estimated by the culture on the Congo red agar.
3) Infection rates of Sh.flex. 2b 17-A or E. coli 0-124S in HeLa cells increased with the lapse of infection time and the rate reached 36% or 13% in 8 hours, respectively. However, such increase was not seen on the experiment with Sh. flex. 2b 17-N or E. coli 0-124R.
4) In the case where HeLa cells were infected with both the virulent strain and the avirulent strain simultaneously, using Shigella or E. coli, the infection rates decreased to around 50% and also numbers of live bacteria in HeLa cells decreased markedly as compared with the case of the infection with the virulent strain only. In HeLa cells, mainly Sh. flex. 2b 17-A or E. coli 0-124S formed colonies on Congo red agar.
5) Virulent strains (Sh. flex. 2b 17-A, E. coli 0-124S) evoked keratoconjunctivitis of guinea pigs (KC test) and loop inflammation of rabbits (De test), whereas, avirulent strains (Sh.flex. 2b 17-N, E. coli 0-124R) did not evoke them. When eyes or loops were infected with the virulent strain and the avirulent strain simultaneously, it was found that an increased number of bacteria was needed to evoke the same degree of inflammation as the virulent strain only.
6) On the mixed infection in KC test or De test, only the virulentstrains (Sh. flex. 2b17-A, Ecoli 0-124S) were isolated from inflammed samples.
