Inactivation of Staphylococcus Bacteriophage by Trypsin. ∗

Abstract

It is already known that bacteriophages active on intestinal organisms exhibit a high degree of resistance to the action of trypsin. With the exception of a trypsin-susceptible Shiga bacteriophage reported by Wollman, 1 this resistance seemed to extend itself to bacteriophages in general. Indeed, Arnold and Weiss 2 were able by trypsinization to free the lytic filtrates of bacterial and other proteinaceous residue. During the course of similar studies in the laboratory of d'Herelle at Alexandria, the writer had occasion to trypsinize a variety of lytic filtrates with the object of freeing them of these protein residues. In the course of this work it was discovered that 2 “races” of staphylococcus bacteriophage were rendered inactive by trypsin within a period of about 48 hours. The 2 “races” in question had been isolated by Dr. Gratia of the Pasteur Institute at Brussels. One of them appeared to be active only on one strain of staphylococcus, whereas the other was capable of lysing a number of staphylococcus strains. Both were highly active and produced complete clarification of homologous bacterial suspensions, and this better at 33° C. than at 37° C.

The experiments were originally carried out as follows: A small quantity (2-5%) of powdered trypsin† was emulsified in a freshly lysed culture and the treated filtrate was then filtered through coarse filter paper to remove the larger particles from the suspension. To this treated filtrate was then added about 2% of chloroform to inhibit bacterial growth. A capillary tube of heated egg-white was dropped into the mixture to serve as an indicator of the progress of tryptic activity. These suspensions were incubated at 37° C., the optimum temperature for tryptic digestion, for periods of 48 hours or longer. As a rule the chloroform served to keep the suspensions free of bacterial growth, so that it was possible in most instances to test the lytic activity of the trypsinized filtrate at frequent intervals without preliminary filtration through a Chamberland candle.