Virtual Poster 21st Lancefield International Symposium for Streptococci and Streptococcal Diseases 2022

Background The rapid increase in the rate of erythromycin resistance among streptococcal isolates has been reported worldwide in the past two decades. However, in the recent years, the studies were mainly focused on Streptococcus pneumoniae and Streptococcus pyogenes. The aim of this study was to explore genetic element carrying mefG gene (which confers efflux-mediated erythromycin resistance) and their linkage with tetracycline resistance determinants in Streptococcus dysgalactiae subsp. equisimilis (SDSE) isolate NT15 recovered from the child with acute pharyngotonsillitis in Vietnam.

Methods Whole genome sequencing was done using MiSeq technology. Genome sequence has been deposited in GenBank (JAFELF010000002.1).

Results The computer analysis revealed that in strain NT15 the mefG gene was located within 152 kb contig (NODE_2) on a prophage-associated genetic element (54,700 bp). This element consisted of 54 ORFs and was chimeric in nature; it derived from insertion of Tn1207.1 related transposon into streptococcal prophage. BLASTN analysis revealed the high similarity of this prophage to others, Tn1207.1 (52,491 bp) and Ф10394.4 (58,761 bp), discovered in tetracycline-susceptible S. pyogenes. In both S. pyogenes and NT15 strains these phages were integrated into the same chromosomal gene (comEC). Major difference between S. pyogenes and TN15 phages was the presence of 5 kb region containing unique lsaE and lnuB genes encoding resistance to lincosamides in NT15, which seems to be acquired from nonstreptococcal species. Tetracycline susceptibility in NT15 strain was associated with presence of silent tetS gene in Tn916.

Conclusions Continued surveillance of macrolide resistance and clonal composition among SDSE is necessary to determine genetic stability of clones and to guide therapy strategies.