Abstract
A total of 394 nonduplicate isolates of
Streptococcus pyogenes
collected from 1979 to 1998 and 267 nonduplicate isolates of
Streptococcus pneumoniae
collected from October, 1998, to May, 1999,
in Taiwan were evaluated. Among the 220 erythromycin-resistant (MIC, ≥1
μ
g/ml)
S. pyogenes
isolates, 35% had an M phenotype and 65% had an ML phenotype (inducible resistance [iML], 0.5%,
and constitutive resistance [cML], 64.5%). Among the 243 erythromycin-resistant
S. pneumoniae
isolates, the majority (65.4%) had an ML phenotype (iML, 0.4%, and cML, 65%) and 34.6% had an M phenotype.
A substantial upsurge in the incidence of M-phenotype erythromycin-resistant isolates was found with time for
S. pyogenes
(0% in 1979-1984 and 100% in 1997-1998), and an increasing incidence of M-phenotype
among erythromycin-resistant
S. pneumoniae
was also noted (S. pyogenes
and all but four
S. pneumoniae
isolates exhibiting a cML or iML phenotype
had harbored the
ermAM
gene. The presence of the
mefA
gene was demonstrated in all isolates of
S. pyogenes
and the
mefE
gene in all but four
S. pneumoniae
isolates exhibiting
the M phenotype. Due to the increasing susceptibility of
S. pyogenes
and
S. pneumoniae
isolates to clindamycin, susceptibility tests of these two organisms to macrolides and clindamycin should
be performed simultaneously in the clinical microbiology laboratory, particularly in areas with high rates of macrolide resistance.