Further Observations on Specific Inhibition of Bacteriophage Action

Abstract

Recently we described¹ specific inhibition of bacteriophage by bacterial extracts (B. dysenteriae Shiga and B. paratyphosus B). To test further the specificity of the inhibition, experiments were made with phages and extracts of organisms within the salmonella group, namely, B. paratyphosus B and B. suipestifer. Both phages were derived from chicken stool filtrates and were specific in their reactions on the 2 cultures.

The extracts were dissolved in saline with the aid of weak alkali and heat, neutralized, diluted with saline to make a 1-200 solution, and passed through Seitz filters. Suitable dilutions of the 2 phages in beef extract broth were prepared and mixed with equal quantities of the filtered bacillary extracts. Two tests were made with these mixtures; one after incubation overnight at 37°∗ and another following an additional interval of 12 hours at the same temperature. One-half cc. was removed from each one of the tubes, diluted with 4.5 cc. of beef extract broth and the homologous test organism was added.

The course of lysis in both tests showed that the action of anti-B. suipestifer phage was inhibited by its homologous extract, but only slightly by an extract of B. paratyphosus B.; on the other hand, the extract of B. suipestifer but weakly influenced the action of anti B. paratyphosus B. phage which was inhibited to a considerable degree by the B. paratyphosus B. extract. The effects were pronounced in both tests but the results were somewhat better in the mixtures incubated for the longer period.

Furthermore, the course of lysis of the anti-B. suipestifer phage was normal when placed in contact with extracts of B. stanley, B. aertryck, and B. dysenteriae (Shiga).

Other experiments were made to determine the relationship between phage titre and inhibition by extracts of various organisms acted on by a related phage.