Screening method for detecting staphylococci with reduced susceptibility to teicoplanin

The incidence of infections caused by staphylococci with decreased suscepti bility to teicoplanin (MIC greater than or equal to 8 mu g/ml) is increasin g, but the disk diffusion test has difficulty detecting this low level of r esistance. In addition, detection is complicated because of the heterogeneo us phenotypes for teicoplanin. In this study, we evaluated an agar screenin g method to detect staphylococci with decreased susceptibility to teicoplan in or heterogeneous resistance. First, to investigate the inoculum density and teicoplanin concentration of screening agar, we used 10(5) and 10(6) CF U/ml and Mueller-Hinton agars supplemented with 6 and 8 mu g of teicoplanin /ml to test 39 genetically distinct staphylococcal strains (15 strains with teicoplanin MICs greater than or equal to 8 mu g/ml and 24 strains with te icoplanin MICs greater than or equal to 4 mu g/ml). On the basis of the res ults obtained, a final inoculum of 106 CFU/spot and a teicoplanin concentra tion of 8 mu g/ml were selected. By this screening method, all strains havi ng teicoplanin MICs greater than or equal to 8 mu g/ml or showing heterores istance could be detected. These findings indicate that the method can be u sed as a reliable screening method for detecting staphylococci with reduced susceptibility to teicoplanin. (C) 2000 Elsevier Science B.V. All rights r eserved.