Antimicrobial susceptibility and survey of macrolide resistance mechanisms among Streptococcus pyogenes isolated in Rio de Janeiro, Brazil.
A total of 357 clinical Streptococcus pyogenes isolates collected between 1994 and 1999 in Rio de Janeiro city were tested for susceptibility to 10 antimicrobial drugs by agar-diffusion tests. All isolates were susceptible to penicillin, cephems, and vancomycin. High resistance rates were observed for tetracycline (43.1%) and trimethoprim/sulfamethoxazole (77.9%). Three isolates (0.8%) were resistant to erythromycin, and three exhibited intermediate susceptibility. Determination of the erythromycin MICs by the agar dilution method, showed 1.6% of erythromycin resistant isolates (the three erythromycin-resistant and the three erythromycin-intermediate isolates found by agar-diffusion test). Of the erythromycin-resistant isolates subjected to the double-disc diffusion test for erythromycin and clindamycin, three isolates expressed the iMLSB and three the M phenotype. The resistance phenotypes were confirmed by comparing the clindamycin MICs determined under normal testing conditions and those determined after induction by pre-growth in 0.06 microg/ml of erythromycin. Three ermTR and three mefA-containing isolates were detected by PCR. In strains belonging to the iMLSB phenotype, two clones were identified by PFGE following restriction with SmaI. M phenotype isolates could not be restricted with SmaI. Our results indicate a low rate of erythromycin resistance among S. pyogenes isolated in Rio de Janeiro, Brazil, and pointed to the presence of both resistance mechanisms found in streptococci.
d'Oliveira
R E C
RE
Instituto de Microbiologia, Universidade Federal do Rio de Janeiro/UFRJ, Rio de Janeiro, 21941-590, Brazil.
Barros
R R
RR
Mendonça
C R V
CR
Teixeira
L M
LM
Castro
A C D
AC
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001938:Brazil; D015169:Colony Count, Microbial; D024881:Drug Resistance, Bacterial; D016521:Electrophoresis, Gel, Pulsed-Field; D005838:Genotype; D006801:Humans; D018942:Macrolides; D016133:Polymerase Chain Reaction; D013297:Streptococcus pyogenes / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification
D000900:Anti-Bacterial Agents; D018942:Macrolides