BD Taxo™ P Discs are impregnated with ethylhydrocupreine hydrochloride (optochin), a drug used for pneumonia therapy before sulfonamides became available. The growth of pneumococci, but not of other streptococci, is markedly inhibited by this chemical. Pneumococci may, therefore, be differentiated from other alpha-haemolytic streptococci by the formation of a zone of inhibition around a BD Taxo™ P disc placed on a blood agar plate heavily inoculated with a pure culture suspected to be Streptococcus pneumoniae. 231046 Taxo™ P Discs, Single vial of 50 discs.