The “Source” of the Lytic Principle.

Abstract

Our experiments involve attempts to generate lytic principle by enforcing dissociation through the use of (1) commercial pancreatin extracts unheated, (2) similar extracts heated at 60° C., or sterilized by heat, (3) peptone solutions sterilized by heat, (4) sterile distilled water, and (5) bacterial cultures unmodified by any foreign substance. Three brands of pancreatin were employed, Squibb's, Difco and Armour's. The peptone was the Parke Davis Co. “bacteriologic peptone.” The cultures used comprised a stock strain of the Shiga dysentery bacillus and a strain of B. coli (Jordan). In both species, fully sensitive, S type cultures relatively free from O and R forms were employed.

Pancreatin extracts were prepared in sterile broth having a pH of 7.8. First, varying amounts, heated at 60° C. or unheated, filtered (Berkefeld N) or unfiltered, were placed in contact with young Shiga and coli broth culture on sterile 20 cm. agar plates. Such plates were found to tolerate loading with even 1.0 to 1.5 cc. of the extract, spread evenly over the slightly dried surface. No sign of lytic areas was observed after incubation. The same extracts, however, heated at 60° C. for 30 minutes and filtered through a Berkefeld N candle, when added in much smaller amounts to tubes of broth seeded with young Shiga culture, resulted in the generation of active lytic principle within two to six serial filtrations. Minute amounts of the principle so generated always registered directly by the production of lytic areas when the plate method was employed. The Squibb pancreatin extracts were the most effective, yielding active lytic principle in the Shiga cultures after the first filtration. This was followed by Difco pancreatin (fourth filtrate) and by Armour's pancreatin (sixth filtrate). Only the Squibb pancreatin caused the generation of lytic principle in cultures of B. coli (fifth filtrate).