Prevalence and mechanisms of macrolide resistance in clinical isolates of group A streptococci from Ontario, Canada

A total of 3,205 group A streptoccal isolates were collected in 1997 throug h a private laboratory which serves community physicians in southern Ontari o and which represents a population base of 6 million people. Nonsusceptibi lity to erythromycin was detected for 67 (2.1%) isolates both by disk diffu sion and by broth microdilution. Of these, 47 (70%) were susceptible to cli ndamycin and were found by PCR to possess the mef gene. Of the other 20 str ains, 18 and 2 showed inducible and constitutive resistance, respectively, to clindamycin. Nineteen of these strains were show by PCR to possess the e rmTR gene, and a single constitutively resistant strain harbored an ermB ge ne. Sixteen (24%) erythromycin-resistant strains were also resistant to tet racycline, All were susceptible to penicillin and chloramphenicol.