The Uptake of Salmonella typhi by Phagocytes and its Intracellular Viability

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Abstract
In the course of in vivo phagocytosis experiments with S. typhi the living intracellular count dropped more intensively than the total intracellular count, indicating that the morphological integrity of the bacterial cells did not necessarily indicate their viability. Thus, three different steps of the process were observed: uptake, devitalization and digestion of the engulfed microorganisms. In the abdominal cavity of living mice, only a few virulent bacteria (strain Ty2) were engulfed by phagocytes, they partly lost their viability, but the morphological structure of the majority of them remained intact. After several hours they were able to multiply intracellularly and a strong capsule formation of the intracellular grown virulent bacteria was observed. Avirulent bacteria (strain O 901) were easily engulfed and lost both their viability and morphological structure. Acetone-killed bacteria (virulent and non-virulent) remained microscopically visible in the phagocytes for more than 8 hours, indicating that the phagocytes were unable to digest them. In the abdominal cavity of dead mice virulent bacteria behaved as in the abdominal cavity of living mice. Avirulent microorganisms were engulfed, devitalized, but did not lose their morphological structure and affinity for stains. The digestion, the last step of phagocytosis, took place in living mice only. Extracts of liver and spleen, peritoneal fluid and plasma of infected mice interfered with the uptake of S. typhi, strain O 901, by phagocytes in vitro. Liver extracts effected in vivo a delay of the devitalization and digestion of the intracellular bacteria of strain O 901.