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.1,2
Pneumococci may, therefore, be differentiated from other alpha-hemolytic
streptococci by the formation of a zone of inhibition around a Taxo
P disc placed on a blood agar plate heavily inoculated with a pure
culture suspected to be Streptococcus
pneumoniae.