Failure of Micro Media FOX Microdilution System to detect decreased susceptibility of Streptococcus pneumoniae to penicillin.

Twelve isolates of Streptococcus pneumoniae with decreased susceptibility by oxacillin screen were susceptible by the FOX panel (Micro Media Systems, Cleveland, Ohio), a commercial microdilution system designed for fastidious organisms. These organisms were found to be moderately susceptible or resistant by broth macrodilution and agar dilution methods. This discrepancy indicates that the FOX panel is not reliable for susceptibility testing of S. pneumoniae.