A study on tetracycline resistance genes, tet(B) and tet(C), in the water columns of the East Sea

Abstract

Tetracycline is a broad-spectrum antibiotic, and the bacterial resistance against it has been posing a threat. The tetracycline resistance genes are thought to be transferred from the environment to the pathogens. In this study, 149 tetracycline resistant bacterial strains were isolated from the seawater at various locations in the East Sea and southern Pacific Ocean. In addition, natural DNA was extracted from the water of the East Sea at different depths and locations. The DNA extracted from 48 isolated bacteria as a template was used for PCR to investigate for 38 tetracycline resistance genes. Four new PCR primers were developed with CODEHOP, and they were used in PCR on all 149 bacterial strains and the natural DNA from the seawater. None of the bacterial isolates seemed to carry both recognized- and putative- tet(B) and tet(C), which could be characteristic of culturable tetracycline-resistant bacteria. Only recognized-tet(C) was detected in all 25 seawater samples. There were no spatial variation pattern among the environmental sequences, but approximately 10% of which were unique. Despite the failure of the PCR experiments, the phylogenetic and protein-homology analysis of the putative- tet(B)s and tet(C)s brought forth prospective results. These genes could be classified as new classes of tetracycline resistance genes, possibly existing only in marine environments. Moreover, putative-tet(B)s would be considered as a novel group of tetracycline resistance genes that has never been reported. The putative-Tet(B) proteins turned out to be homologous to the TRAP-TAXI family of proteins which act as substrate binding receptors in secondary transport systems. Not much is known about the TRAP-TAXI system, and they were not known for transporting antibiotics. Given that many TRAP transporters are being found in marine alphaproteobacteria, this revelation could lead to a whole new establishment of marine bacterial resistance to tetracycline.