Protective Action of Typhoid Phage on Experimental Typhoid Infection in Mice

Abstract

Asheshov, Wilson and Topley 1 have reported on the protective effect in mice of typhoid bacteriophage given separately and by routes different from those used in infecting the animals. The preliminary studies here reported confirm the findings of the above investigators and enlarge upon certain aspects of the problem.

A recently isolated strain of Eberthella typhi obtained by blood culture was employed. It forms smooth colonies, is motile, produces typical sugar fermentation reactions and agglutinates specifically with anti-typhoid serum. Organisms from 18- to 24-hour-old cultures grown on veal infusion agar were suspended in mucin∗ according to the methods of Rake 2 and Miller, 3 and mice were infected by the peritoneal route, all inoculations being made with a quantity of 1 cc of the mucin-organism mixtures.

The phage was originally isolated from sewage and is a crude phage which produces several different types of plaques. Filtrates which contained approximately 3.3 × 10⁸ phage particles per cc were used for mouse injection.

Typhoid infection in mice was acute. Blood stream invasion with resulting bacteremia usually occurred within 1 hour following intraperitoneal inoculation and all of the fatally infected control mice died within 24 hours. The minimal fatal dose of the culture varied in 7 virulence tests from 1000 to 10 bacilli, thus the quantity of organisms used in the phage experiments represented from 1000 to 100,000 fatal doses.

The protective effect of phage was tested by various ways in 7 experiments, the results of which may be summarized as follows:

(1) Phage injected immediately before the intraperitoneal inoculation of 1 × 10⁶ typhoid bacilli protected all of 32 mice when injected intravenously and all of 19 mice when administered by the subcutaneous method. Intravenously injected phage also protected against 1 × 10⁷ and 1 × 10⁸ bacilli, but failed to protect against 5 × 10⁸ organisms which may have been due in part to the primary toxicity of such a large number of organisms.