Action of Penicillin on Staphylococcus. Effect of Size of Inoculum on the Test for Sensitivity.

Abstract

163 strains of Staphylococcus were tested for resistance to penicillin, using a broth dilution method. Replicate detns. were made using inocula containing either a few or many cells. It was shown that the action of penicillin against most strains of Staphylococcus is related only in a minor degree to the number of bacteria present. In a not inconsiderable group of strains, somewhat more resistant to penicillin than the majority, the outcome of tests for penicillin sensitivity is profoundly influenced by the number of cells present.