Identification of Novel Mobile Genetic Elements Associated with Resistance to Macrolide and Lincosamide in Streptococcus dysgalactiae subsp. equisimilis

Streptococcus dysgalactiae subsp. equisimilis (SDSE) is an important human pathogen. Recently, several studies have described the incidence of antibiotic resistance for SDSE worldwide, however, the data on the presence of corresponding genes and their possible association with mobile genetic elements are still limited.

The objective of this research was to analyze the macrolide resistance in SDSE and to identify genetic determinants, mechanisms of resistance, and association with mobile genetic elements.

A total of 9 SDSE strains from the collection of Joint Russian-Vietnamese Tropical Research and Technological Center (Hanoi, Vietnam) were used. These strains were previously isolated from throat swabs of children with pharyngotonsillitis in 6 provinces in Vietnam from 2012 to 2015. Antimicrobial resistance was tested by disk diffusion method. The presence of antibiotic resistance genes (ARG) was analyzed by PCR. The strains were characterized by emm typing and multilocus sequence typing (MLST). Illumina sequencing was employed for genome analysis of 4 representative SDSE isolates. Analysis of genetic elements with antibiotic resistance determinants was done using PubMed database and BLAST-searches. Artemis was used for comparative analysis of genetic elements.

In our study, we identified emm types that were similar to those reported in other studies. All SDSE isolates remained susceptible to penicillin, but presented alarming level of resistance to macrolides, tetracyclines, and fluoroquinolones. Most of the erythromycin-resistant strains were also characterized by clindamycin-resistance (MLSB phenotype). Both erm and different alleles of mef genes widely distributed among streptococcus pyogenes and Streptococcus pneumoniae were detected, except erm (TR) gene. The genetic elements carrying resistance determinants showed significant interspecies similarities, indicating conjugative transfer of antibiotic resistance genes between streptococcal species.

Identification of the novel antibiotic resistance genes in SDSE indicates the necessity of monitoring of antibiotic resistance spreading and gene transfer in this bacterium.