POLYMYXIN SUSCEPTIBILITY IN STAPHYLOCOCCI DIFFERENTIATING COAGULASE‐POSITIVE AND COAGULASE‐NEGATIVE STRAINS

Abstract

Staphylococcal reference strains (47) representing 13 spp. were tested for polymyxin sensitivity using tablet and disc diffusion methods. Corresponding minimum inhibitory concentrations and median inhibitory concentrations were determined with a plate dilution assay. Coagulase-positive strains were more resistant towards polymyxin, and could thereby be separated from coagulase-negative strains. Recently isolated staphylococci (100) from clinical specimens were tested; the coagulase-positive strains were again identified by their smaller tablet inhibition zones. Thus, the polymyxin test is an aid in the rapid differentiation of staphylococci in laboratories performing primary sensitivity tests.