Polymyxin susceptibility in staphylococci differentiating coagulase-positive and coagulase-negative strains.

Abstract

47 staphylococcal reference strains representing 13 species were tested for polymyxin sensitivity using tablet and disc diffusion methods. Corresponding MIC and IC50 values were determined with a plate dilution assay. Coagulase-positive strains were found to be more resistant towards polymyxin, and could thereby be separated from coagulase-negative strains. Furthermore, 100 recently isolated staphylococci from clinical specimens were tested, and again the coagulase-positive strains could be identified by their smaller tablet inhibition zones. We conclude that the polymyxin test is an aid in the fast differentiation of staphylococci in laboratories performing primary sensitivity tests.