A New Composite Integrative and Conjugative Element Mediates Multiple Drug Resistance from to .

INTRODUCTION

Integrative and conjugative elements (ICEs) are a category of horizontal mobile genetic elements (MGEs) that play important roles in mediating the spread of antimicrobial resistance in Streptococci.

METHODS

In this study, a novel ICE, namely ICE26_, was identified from commensal through routine silico analyses. The genetic characterization of ICE26_ was explored based on a comparison with known ICEs. The cyclization and cross-species transferability (from to ) of ICE26_ were explored using inverse PCR and conjugation transfer experiments.

RESULTS

ICE26_ is 61.618 kb in length at downstream of and carries multiple antibiotic resistance genes, including (B) [for erythromycin, clindamycin, and streptococcin B (MLS)], (tetracycline), and (E) (clindamycin), and (6)-I (aminoglycosides). The comparative analysis results showed that ICE26_ was a composite ICE with a mosaic structure composed of modules in the ICESa2603 and Tn families. The inverse PCR results demonstrated that ICE26_ could be excised from the chromosome to form a circular intermediate. The conjugation transfer experiment and sequencing results confirmed the cross-species transfer of ICE26_ to recipients at a relatively low frequency (2.13 × 10). Moreover, core functional modules were retrieved from GenBank to search for any ICEs related to ICE26_. Eventually, 53 putative ICEs were identified, including three composite ICEs with high similarity to ICE26_, three ICEs in the Tn family, and 47 ICEs in the ICE2603 family.

DISCUSSION

In this study, a novel mosaic ICE was reported for the first time. In addition, its transfer to the major pathogen was characterized and proved. These findings suggest that this ICE is expected to become a vehicle for the dissemination of multiple antimicrobial resistance through the wider pathogen Streptococci.