Cultures of L929 mouse fibroblast cells infected with the Ty 2 strain of Salmonella typhosa were regularly freed of infection by treatment for prolonged periods of time with synnematin and occasionally by treatment with other antibiotics. Failure to eradicate S. typhosa from the tissue cultures resulted when the experiment was terminated prematurely because of nonspecific death of the host cells or overgrowth of the cultures by antibiotic resistant organisms.

Several hypotheses are discussed concerning the capacity of S. typhosa to persist for long periods of time in antibiotic-treated cultures. Previously, emphasis has been placed on the unique properties of the living cell in protecting the invading organism in the presence of antibiotic. The metabolic state of the organism in the treated infected culture may also be an important factor in its survival in the presence of drug.

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