Optochin Revisited: Defining the Optimal Type of Blood Agar for Presumptive Identification of Streptococcus pneumoniae

To determine the optimal media for optochin susceptibility testing ofStreptococcus pneumoniae , we measured inhibition zones for 72S. pneumoniae and 22Streptococcus viridans isolates on three blood-containing media. Because 15.3, 0, and 22.2% ofS. pneumoniae organisms were misidentified on Columbia agar, Trypticase soy agar (TSA), and Mueller-Hinton agar, respectively, each containing sheep blood, we recommend that TSA-sheep blood agar be used.