Bacitracin Susceptibility Test Discs are used for the identification and differentiation of Group A streptococci (especially S.pyogenes) from other beta-haemolytic streptococci. The growth of Group A beta-haemolytic streptococci on blood agar is inhibited by 0.04 units Bacitracin disc. Micrococci and strep tococci are also inhibited by 0.04 units disc, while all coagulase-negative staphylococci are resistant. Bacitracin sensitivity test along with Furacin and Optochin tests are useful for distinguishing Aerococcus viridans and S.milleri from enterococci and Streptococcus mitis.