Incidence of decreased penicillin sensitivity of Streptococcus pneumoniae from clinical isolates.

One hundred isolates of Streptococcus pneumoniae isolated from clinical specimens over nine months were examined for sensitivity to penicillin using disc tests and minimum inhibitory concentration (MIC) studies. Four per cent of the isolates were found to have reduced sensitivity to penicillin. Penicillin and methicillin discs with 1 unit and 5 micrograms antibiotic, respectively, were inferior to discs with 1 microgram oxacillin, which gave results comparable with those of MIC studies.