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Survival of Ingested Salmonella in the Cockroach Periplaneta Americana

1. Feces from healthy human donors were inoculated with varying doses of S. typhimurium (2 strains) or S. montevideo (2 strains) and the survival of the organisms during storage in closed containers at 15°–25°C. was determined. An appreciable proportion of the number introduced could be recovered in all trials after 2 days, frequently after 5–7 days, sometimes even after 14 days.

2. Adult P. americana which had been starved for a week were allowed to feed on uninfected human feces; the quantity ingested in a single meal was estimated to be approximately 0.02–0.1 gram.

3. Similarly starved P. americana were allowed to feed on human feces to which varying numbers of Salmonella had been recently added; after an interval of 2 or 7 days, the alimentary tracts were removed and cultured for the presence of these organisms. Survival in the gut was demonstrated to occur fairly regularly and to persist for at least 7 days when the insects had ingested in feces approximately 10⁴ or more viable S. typhimurium (strain 5609) or S. montevideo (strain B-33). With smaller doses, recovery of the Salmonella fed was obtained only rarely. The limited data obtained with a second strain of S. montevideo (5327) suggested that it had somewhat less ability to persist than strain B-33.

4. Although the cockroach Periplaneta americana appears to have some mechanism for eliminating many hundreds of ingested Salmonella, if the insect eats feces containing at least several thousand of these microorganisms it may thereafter continue to harbor certain strains for at least a week.