1. In the light-microscopic study on the relationships between tissue-cultured cells and bacteria, it was found that the degree of intracellular growth of infecting microorganisms was in parallel with virulence of the particular strain for animals in which it could cause typhoid infection. It was also revealed that the intracellular growth of a virulent strain of S. enteritidis was inhibited in the mononuclear cells from animals previously immunized with an R-type live vaccine, but not in the cells from animals immunized with an S-type killed vaccine.
2. Phagocytosis of S. enteritidis by peritoneal mononuclear cells from guinea pigs or Kupffer cells of mice was also observed electron-microscopically, and the mechanism of the penetration of bacteria into cytoplasm has been discussed being compared with that of colloidal particles.
3. Some differences were observed between high-virulent and low-virulent strains of S. enteritidis in electron-microscopic findings when they were phagocytized into the above-mentioned cells ; many of low-virulent organisms showed degenerated and swollen appearances with low electron-density surrounded by electron-dense substance, while high-virulent organisms were usually electron-dense and lacked surrounding substance.
This study was conducted by Drs. K. Saito, M. Nakano, K. Hashimoto and T. Akiyama of the Department of Bacteriology, and Dr. I. Yamamoto of the Department of Pathology.
A part of this study was aided by a grant from the Ministry of Education, Japan (Cooperative Research Fund, 1933-1935).
Thanks are due to Dr. T. Kobayashi, Professor of Pathology, and Dr. Y. Watanabe, Assistant Professor of Pathology, for their valuable advice on the electron-microscopic study.