Pneumococci resistant to erythromycin.

Susceptibility to erythromycin was determined for all pneumococci isolated in one laboratory from clinical specimens between 1969 and 1977. All 4724 isolates examined prior to October 1973 were susceptible to erythromycin. From October 1973 to December 1977, 64 (0.71%) of 8995 pneumococcus isolates were resistant to erythromycin. The resistant strains were isolated from 38 patients living in six widely separated communities in Alberta. The erythromycin-resistant strains were of nine capsular types, including six that often cause bacteremic disease and five for which resistance to erythromycin has not been reported hitherto. Certain strains of type 33 and of type 15 were highly resistant, the minimum inhibitory concentration (MIC) of erythromycin being 2000 microgram/mL; these strains were also highly resistant to lincomycin and clindamycin. Resistance in strains of other types was much lower, the MIC of erythromycin being 0.6 to 20 microgram/mL, and all but one of these strains were susceptible to lincomycin and clindamycin. All the erythromycin-resistant pneumococci were suspectible to penicillin.