Characterization of erm (B)-Carrying Integrative and Conjugative Elements Transferred from Streptococcus anginosus to Other Streptococci and Enterococci

Abstract

Integrative and conjugative elements (ICEs) are important vectors of lateral gene transfer and contribute to the evolution of bacterial pathogens. However, studies on the transfer among species and the physiological consequences of ICEs are rare. The objective of this study was to investigate the cross-species transferability of newly identified erm(B)-carried ICE in Streptococcus anginosus San95 and its physiological consequences after transfer. The erm(B)-carried ICE, characterized by a triple serine integrase module, integrated into hsdM genes, thus designated ICESan95_hsdM. Analysis of ICESan95_hsdM revealed 32 additional ICESan95-like ICEs in the available NCBI genome (n = 24) and sequence of clinical isolates (n = 8). Polymerase chain reaction (PCR) was used to evaluate the 467 clinical isolates, of which 84 were positive for core genes (integrase, relaxase, and T4SS genes) of ICESan95_hsdM. Cross-species transfer experiments demonstrated that ICESan95_hsdM could transfer from S. anginosus to different streptococcal and enterococcal recipients. Growth and competitive culture assays showed acquisition of ICESan95_hsdM incurred no fitness cost. Our work discovered a group of ICEs in Streptococci and Enterococci. For the first time, we demonstrated the broad cross-species transferability to different species or genera of ICEs with no fitness cost that enables commensal S. anginosus to deliver antimicrobial resistance genes to other streptococci and enterococci.