Genomic and functional insights into antibiotic resistance genes and linked with the SXT element of non-O1/non-O139.

The emergence and spread of antibiotic-resistant bacterial pathogens are a critical public health concern across the globe. Mobile genetic elements (MGEs) play an important role in the horizontal acquisition of antimicrobial resistance genes (ARGs) in bacteria. In this study, we have decoded the whole genome sequences of multidrug-resistant clinical isolates carrying the ARG-linked SXT, an integrative and conjugative element, in their large chromosomes. As in others, the SXT element has been found integrated into the 5'-end of the gene (which encodes peptide chain release factor 3 involved in translational regulation) on the large chromosome of non-O1/non-O139 strains. Further, we demonstrate the functionality of SXT-linked and genes, which confer resistance to chloramphenicol and streptomycin, respectively. The gene-encoded protein FloR belongs to the major facilitator superfamily efflux transporter containing 12 transmembrane domains (TMDs). Deletion analysis confirmed that even a single TMD of FloR is critical for the export function of chloramphenicol. The gene has two putative promoters, P1 and P2. Sequential deletions reveal that P2 is responsible for the expression of the . Deletion analysis of the N- and/or C-terminal coding regions of established their importance for conferring resistance against streptomycin. Interestingly, qPCR analysis of the and genes indicated that both of the genes are constitutively expressed in cells. Further, whole genome-based global phylogeography confirmed the presence of the integrative and conjugative element SXT in non-O1/non-O139 strains despite being non-multidrug resistant by lacking antimicrobial resistance (AMR) gene cassettes, which needs monitoring.