Optochin-resistant variants of Streptococcus pneumoniae

Abstract Ten Streptococcus pneumoniae clinical isolates, possessing physiologically typical pneumococcal characteristics, showed optochin-susceptible and optochin-resistant colonies around the optochin disk, when tested for optochin susceptibility. Equivocal optochin disk test results should be confirmed by bile solubility, agglutination tests, or both.