Phenotypes and genotypes of erythromycin-resistant Streptococcus pyogenes strains isolated from invasive and non-invasive infections from Mexico and the USA during 1999-2010.
OBJECTIVE
To compare the prevalence, phenotypes, and genes responsible for erythromycin resistance among Streptococcus pyogenes isolates from Mexico and the USA.


METHODS
Eighty-nine invasive and 378 non-invasive isolates from Mexico, plus 148 invasive, 21 non-invasive, and five unclassified isolates from the USA were studied. Susceptibilities to penicillin, erythromycin, clindamycin, ceftriaxone, and vancomycin were evaluated according to Clinical and Laboratory Standards Institute (CLSI) standards. Phenotypes of erythromycin resistance were identified by triple disk test, and screening for mefA, ermTR, and ermB genes was carried out by PCR.


RESULTS
All isolates were susceptible to penicillin, ceftriaxone, and vancomycin. Erythromycin resistance was found in 4.9% of Mexican strains and 5.2% of USA strains. Phenotypes in Mexican strains were 95% M and 5% cMLS; in strains from the USA, phenotypes were 33.3% iMLS, 33.3% iMLS-D, and 33.3% M. Erythromycin resistance genes in strains from Mexico were mefA (95%) and ermB (5%); USA strains harbored ermTR (56%), mefA (33%), and none (11%). In Mexico, all erythromycin-resistant strains were non-invasive, whereas 89% of strains from the USA were invasive.


CONCLUSIONS
Erythromycin resistance continues to exist at low levels in both Mexico and the USA, although the genetic mechanisms responsible differ between the two nations. These genetic differences may be related to the invasive character of the S. pyogenes isolated.
Molecular Microbiology Laboratory, Centro de Investigación Biomédica de Occidente, Instituto Mexicano del Seguro Social, Sierra Mojada 800, Col. Independencia, Código Postal 44340 Guadalajara, Jalisco, Mexico. avillase@prodigy.net.mx
Alberto
A
Villaseñor-Sierra
Eva
E
Katahira
Abril N
AN
Jaramillo-Valdivia
María de los Angeles
Mde L
Barajas-García
Amy
A
Bryant
Rayo
R
Morfín-Otero
Francisco
F
Márquez-Díaz
Juan Carlos
JC
Tinoco
José
J
Sánchez-Corona
Dennis L
DL
Stevens
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002443:Ceftriaxone / Q000494:pharmacology; D002648:Child; D002675:Child, Preschool; D002981:Clindamycin / Q000494:pharmacology; D024881:Drug Resistance, Bacterial; D004917:Erythromycin / Q000494:pharmacology; D005838:Genotype; D006801:Humans; D007223:Infant; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism; D008800:Mexico / Q000453:epidemiology; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D010406:Penicillins / Q000494:pharmacology; D010641:Phenotype; D015995:Prevalence; D013290:Streptococcal Infections / Q000453:epidemiology*; D013297:Streptococcus pyogenes / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D014481:United States / Q000453:epidemiology; D014640:Vancomycin / Q000494:pharmacology; D055815:Young Adult
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; C117866:MefA protein, Streptococcus; D008565:Membrane Proteins; D010406:Penicillins; C551474:ermB protein, Streptococcus pyogenes; D002981:Clindamycin; D004917:Erythromycin; D014640:Vancomycin; D002443:Ceftriaxone; C111078:ErmTR protein, bacteria; D008780:Methyltransferases