The Filterability of Bacteria

Abstract

If one filters a 1:30,000 solution of night blue, a colloidal basic dye, through a siliceous filter- Berkefeld N, the filtrate is colorless.

If, now, we add a so-called “wetting agent” to the dye solution it is found that the dye passes the filter. A number of such agents have been tried, of which I give a partial list: Blood serum, bile, sodium taurocholate, glycocholic acid, turkey red oil, mucin, soap, castor oil soap, lecithin, sodium lauryl sulfate, etc.

Similarly, one can, by adding such agents before inoculation to nutrient broth cultures of bacteria which are non-filterable through siliceous filters when grown on broth without such agents, render the bacteria filterable. The following experiments will illustrate:

The experiments were made as follows : In each case the filter flask contained before sterilization 100 cc of the nutrient broth plus any addition which was used in the broth culture which was to be filtered, so that the filtrate passed directly into fresh, sterile material without further handling.

The ordinary laboratory meat broth is made by extracting ground lean beef in the cold room for 24 hours, then autoclaving at 120°C for 30 min, adding NaCl and peptone, and filtering and adjusting the pH to the required degree.