Survey of macrolide resistance phenotypes in Swedish clinical isolates of Streptococcus pyogenes.

Two hundred selected Swedish clinical strains of Streptococcus pyogenes, identified as erythromycin-resistant and isolated between 1980 and 1988, and 37 consecutive, resistant strains from 1989-90 were examined for resistance phenotype by disc diffusion. Strains constitutively resistant to macrolides, lincosamides and streptogramin B were absent in 1980-85 but accounted for 10% in 1986-88. The majority of the isolates belonged to a recently reported, non-inducible phenotype, described as having low-level resistance to erythromycin and sensitivity to clindamycin (82% in 1980-85, 50% in 1986-88). A significant proportion of the isolates did not agree with any known phenotype and therefore were considered as having one of three novel resistance subphenotypes. Most of the 37 strains from 1989-90 belonged to a novel subphenotype.