Differentiation of Staphylococcus and Micrococcus spp. with the Taxo A bacitracin disk

Taxo A bacitracin disks (BBL Microbiology Systems, Cockeysville, Md.) were evaluated as a test for differentiating staphylococci from micrococci in clinical laboratories. All staphylococci tested were resistant to the disks, with no zone of growth inhibition. Zones of growth inhibition ranging from 10.5 to 25.0 mm in diameter were observed with all micrococci except two isolates which failed to grow on the test medium. These findings were confirmed by minimal inhibitory concentrations to bacitracin. Staphylococci had minimal inhibitory concentrations significantly higher than those of micrococci, with no overlap in the ranges of values.