Screening method for detecting staphylococci with reduced susceptibility to teicoplanin

The incidence of infections caused by staphylococci with decreased susceptibility to teicoplanin (MIC≥8 μg/ml) is increasing, but the disk diffusion test has difficulty detecting this low level of resistance. In addition, detection is complicated because of the heterogeneous phenotypes for teicoplanin. In this study, we evaluated an agar screening method to detect staphylococci with decreased susceptibility to teicoplanin or heterogeneous resistance. First, to investigate the inoculum density and teicoplanin concentration of screening agar, we used 10⁵ and 10⁶ CFU/ml and Mueller-Hinton agars supplemented with 6 and 8 μg of teicoplanin/ml to test 39 genetically distinct staphylococcal strains (15 strains with teicoplanin MICs≥8 μg/ml and 24 strains with teicoplanin MICs≤4 μg/ml). On the basis of the results obtained, a final inoculum of 10⁶ CFU/spot and a teicoplanin concentration of 8 μg/ml were selected. By this screening method, all strains having teicoplanin MICs≥8 μg/ml or showing heteroresistance could be detected. These findings indicate that the method can be used as a reliable screening method for detecting staphylococci with reduced susceptibility to teicoplanin. Copyright (C) 2000 Elsevier Science B.V.