Bacitracin test is used to determine the effect of a small amount of bacitracin (0.04 U) on an organism. Streptococcus pyogenes (group A streptococci) is inhibited by the small amount of bacitracin in the disk; other beta-hemolytic streptococci usually are not.
Bacitracin is a bactericidal drug useful in the treatment of superficial skin infections but too toxic for systemic use. Bacitracin is a polypeptide antibiotic produced by Bacillus subtilis. This drug interferes in the peptidoglycan synthesis of Bacteria. The presumptive identification of group A streptococci (GAS) is usually done by testing for sensitivity to bacitracin.