Novel Mobilizable Genomic Island GEI-D18A Mediates Conjugational Transfer of Antibiotic Resistance Genes in the Multidrug-Resistant Strain sp. D18.

Aquatic environments act as reservoirs of antimicrobial-resistant bacteria and antimicrobial resistance (AMR) genes, and the dissemination of antibiotic resistance from these environments is of increasing concern. In this study, a multidrug-resistant bacterial strain, identified as sp. D18, was isolated from the sea water of an industrial maricultural system in the Yellow Sea, China. Whole-genome sequencing of D18 revealed the presence of a novel 25.8 kb antibiotic resistance island, designated GEI-D18A, which carries several antibiotic resistance genes (ARGs), including , , , (B), , , and three genes. Besides, integrase, transposase, resolvase, and recombinase encoding genes were also identified in GEI-D18A. The transferability of GEI-D18A was confirmed by mating experiments between sp. D18 and 25DN, and efflux pump inhibitor assays also suggested that (B) in GEI-D18A was responsible for tetracycline resistance in both D18 and the transconjugant. This study represents the first characterization of a mobilizable antibiotic resistance island in a species of and provides evidence that spp. could be important reservoirs and vehicles for ARGs in the Yellow Sea area.