Avaliação da colonização orofaríngea por estreptococos beta-hemolíticos

Abstract

Beta-hemolytic streptococci comprise several species of clinical importance. Streptococcus pyogenes (group A streptococci – GAS) is etiological agent of several infections including pharyngitis, being in this case, requires suitable diagnostic and treatment due to the risk of evolution to non-suppurative processes. Other species such as Streptococcus dysgalactiae subsp equisimilis (groups C and G – SDSE), Streptococcus agalactiae (group B streptococci – GBS), Streptococcus anginosus group (SAG) are involved in pharyngitis and other infections. GAS and SDSE share virulence factors, among them, M protein, considered the most important epidemiological marker. In GBS, the polysaccharide capsule is an important virulence factor and epidemiological marker. Penicilin is the drug of choice for treatment of streptococcal infections. Macrolides and lincosamides are recommended therapeutic alternatives, however the increase of resistance to these antibiotics has been reported. This study evaluated the ocurrence of colonization and persistence in 121 children and 127 young adults (YA), students of institutions located in the city of Niteroi, during September 2015 to February 2017, antimicrobial susceptibility and genetic diversity of isolates recovered. Oropharynx secretions were cultured and carriers were submitted to quarterly screening up to 12 months, while persistent colonization could be detected. Isolates were identified by phenotypical and serological tests. Susceptibility tests for seven antibiotics were performed by disk-diffusion technique. Erythromycin resistant isolates were submitted to macrolide resistance phenotype, genotype and minimal inhibitory concentration (MIC) determination by gradient diffusion antibiotic. emm gene typing, the gene that codes M protein, and capsular typing were performed by PCR, followed by emm gene sequencing. The evaluation of genetic diversity was performed by pulsed field gel electrophoresis (PFGE) or random amplified polymorphic DNA (RAPD). Initially, 34 isolates were recovered: 17 isolates recovered from children (all GAS) and 17 from YA [GAS (3), GBS (4), SDSE (8) and SAG (2)]. During persistence evaluation, 10 GAS isolates were recovered from children in six months of screening, while 22 isolates [GAS (2), GBS (2), SDSE (17) and SAG (1)] recovered from young adults during one year. Exchange of species (GAS/SDSE and SAG/GBS) and SDSE serological group was observed in two volunteers during the screening. Isolates were susceptible to ceftriaxone, levofloxacin, penicilin and vancomycin. GAS, GBS and SDSE isolates were resistant to tetracycline. Resistance to erythromycin was also detected: one GAS isolate (iMLSB, ermA, MIC-Eri 8 μg/ml) and six SDSE, whose phenotypes and genotypes were M/mefA/E, iMLSB/ermA and MIC-Eri 8-16 μg/ml. Six emm types were found among GAS isolates, being emm87.16 and emm89.0 the most frequent, detected only among pediatric volunteers. Among SDSE, five emm types with some subtypes were found. Three new emm subtypes were identified in this study, including the most frequent emm87.16. Three GBS capsular types were detected (Ia, Ib and III). A close correlation was observed among emm types diversity and PFGE profiles, where six clonal groups were found among GAS isolates and 10 among SDSE isolates. Among GBS, there are four or five clonal groups, considering digestion with different enzymes. Although the species were not determined, a single clonal group was observed among SAG.