Influence of AHL and Imipenem on bla_NDM Conjugation and sRNA Rydb Expression in Escherichia coli

The rise of carbapenem resistance in Escherichia coli is mainly due to the rapid spread of carbapenemase-encoding genes through horizontal gene transfer, particularly via bacterial conjugation. Recent research has highlighted the role of a small RNA molecule known as RydB in bacterial conjugation, specifically through its interaction with the protein SdiA. This study investigated the effects of sub-inhibitory concentrations of imipenem and N-acyl homoserine lactones (AHLs) on the expression of rydB in E. coli strains that overexpress sdiA. Additionally, we examined how AHLs influence the bacterial conjugation of plasmids that contain carbapenem resistance genes. We selected a carbapenem-resistant isolate of E. coli harbouring the bla_NDM gene and its corresponding plasmid-cured derivative, based on the overexpression of the sdiA gene in response to AHLs. Conjugation experiments were conducted, both without AHL treatment and with AHL treatments, to assess the transferability of the bla_NDM plasmid. The transcriptional response of rydB gene was evaluated in the plasmid-cured derivative, the native type, the transconjugant, and E. coli J53. Our findings indicated that AHLs and imipenem inhibit the expression of the rydB gene. Interestingly, while RydB does not seem to impact bacterial conjugation when suppressed by these agents, the combination of AHLs enhances the conjugation of plasmid that carry the bla_NDM gene. This study enhances our understanding of the regulatory roles that quorum sensing signal molecules, including C4 AHL and C12AHL, as well as imipenem, play in bacterial conjugation and sRNA expression.