optochin optochin optochin (or ethylhydrocupreine hydrochloride) is a derivative of quinine introduced in 1911 by morgenroth and levy with the intention to treat pneumococci infection. in very high dilutions, it inhibits the growth of representatives of all four groups of pneumococci in vitro. that is the main reason it is now used in bacteriology for the differentiation of streptococcus pneumoniae, which is optochin-sensitive, from the other, resistant alpha-hemolytic streptococci, sometimes called the viridans streptococci because of the green colouration on blood agar around colonies. optochin names iupac name (4β,8α,9r)-6'-ethoxy-10,11-dihydrocinchonan-9-ol other names ethylhydrocupreine identifiers cas number 522-60-1 y 3d model (jsmol) interactive image chebi chebi:86455 n chembl chembl534999 n chemspider 79283 n echa infocard 100.007.577 mesh optochin pubchem cid 71542 unii 4w030vs2og y comptox dashboard (epa) dtxsid50893924 inchi inchi=1s/c21h28n2o2/c1-3-14-13-23-10-8-15(14)11-20(23)21(24)17-7-9-22-19-6-5-16(25-4-2)12-18(17)19/h5-7,9,12,14-15,20-21,24h,3-4,8,10-11,13h2,1-2h3/t14-,15-,20-,21+/m0/s1 nkey: suwzhlcnfqwnpe-latrnwqmsa-n ninchi=1/c21h28n2o2/c1-3-14-13-23-10-8-15(14)11-20(23)21(24)17-7-9-22-19-6-5-16(25-4-2)12-18(17)19/h5-7,9,12,14-15,20-21,24h,3-4,8,10-11,13h2,1-2h3/t14-,15-,20-,21+/m0/s1key: suwzhlcnfqwnpe-latrnwqmbv smiles cc1cn2cc1c2(c3ccnc4c3cc(cc4)occ)o properties chemical formula c21h28n2o2 molar mass 340.46 g/mol except where otherwise noted, data are given for materials in their standard state (at 25 °c , 100 kpa). n verify (what is yn ?) infobox references the growth of bacteria that are optochin-sensitive will show a zone of inhibition around an optochin disc, while the growth of bacteria that are resistant to optochin will not be affected. in vitro, a minimum inhibitory concentration (mic) of 1:10,000,000 will inhibit the growth of pneumococci, and 1:500,000 is bactericidal. resistance for decades, streptococcus pneumoniae has been considered susceptible to optochin; but some strains have been found to be resistant to optochin in laboratory testing. this is notable because the emergence of optochin-resistant strains would invalidate the distinguishing test described above.