Differentiation of serologic group A streptococci from group C and G using disks with various bacitracin levels

It was revealed that a diameter of the inhibition zone of 10 mm or more surrounding a disk with 0.04 U bacitracin differentiates reliably strains of the serological group A form strains of group C and G with the exception of 7.3% strains of group C and G with a high susceptibility for bacitracin. The disks with a higher bacitracin content gives less reliable results.