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The Cockroaches Blaberus Craniifer and Blaberus Discoidalis as Vectors of Salmonella Typhosa

A useful method of mounting Blaberus species is described which allows controlled feeding of test organisms. Salmonella enteritidis was excreted up to 17 days after being fed, while S. typhosa was recovered in only one instance, and that was on the first day. An in vitro test showed an antibacterial agent to be present in the crops of the roaches tested. Measurements with a microquinhydrone electrode revealed crop pH values ranging from 3.9 to 4.9 with the majority of the readings around 4.5. It was shown that typhoid cells are destroyed in vitro at pH values below 4.7, whereas S. enteritidis is more re-resistant. Organisms resembling Propionibacterium freudenreichii were isolated from crops and were shown to exhibit zones of inhibition on agar plates when tested against S. typhosa. The effect appeared to be due to acid production by the isolates. The in vivo antibacterial effect is probably due to the acid produced in the crop of the roaches through the action of micro-organisms.

Attempts to demonstrate bacteriophage activity that might account for the destruction of typhoid organisms in roaches were unsuccessful.