DETECTION AND PREVALENCE OF PNEUMOCOCCI WITH INCREASED RESISTANCE TO PENICILLIN

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  • 1 January 1977
    • journal article
    • research article
    • Vol. 117  (10) , 1159-1161
Abstract
Susceptibility to penicillin was determined for 6000 strains of pneumococci [Streptococcus pneumoniae] isolated during 1974-76 from patients in Alberta and the adjacent region of the Northwest Territories [Canada]. Strains were considered to be relatively resistant if the minimum inhibitory concentration (MIC) of penicillin was 0.16 .mu.g (0.26 U)/ml or more, which is 8 or more times greater than the MIC for fully susceptible strains. Resistance was detected in 143 strains (2.4%) isolated from 122 patients and belonging to 4 capsular types. The MIC of the most resistant strains was 0.32 .mu.g (0.53 U)/ml. Penicillin-resistant strains were highly resistant to oxacillin, the MIC being at least 30 times greater than that for penicillin-susceptible strains. Pneumococci resistant to penicillin may readily be detected by the narrowness or absence of a zone of inhibition around a 1-.mu.g oxacillin disk in susceptibility tests on blood agar. The degree of resistance reported here is relative and does not necessarily preclude successful treatment with full therapeutic doses of penicillin G, but penicillin preparations that give low blood concentrations may not be suitable for treating infections caused by these strains.