Characterization and fitness cost analysis of two plasmids carrying different subtypes of bla in aquaculture farming.

In recent years, the bla gene, which mediate resistance to carbapenems, has disseminated all over the world, and has also been detected in animals. Understanding the dissemination and accumulation of antibiotic resistance genes (ARGs) in a human-impacted environment is essential to solve the food safety problems caused by antibiotics. In this study, two strains of carbapenem bacteria carrying bla were screened from 244 strains isolated from two T. sinensis farms in Zhejiang province, China. After their plasmids were isolated and sequenced, their structure and gene environment were analyzed and the mechanism of bla gene transfer was explored. The study measured the fitness cost of plasmids carrying different bla subtypes by four biological characteristics experiments. The results showed that the fitness cost of IncC plasmid carrying bla was higher than that of IncX3 plasmid carrying bla. Furthermore, the real-time PCR showed that the decrease of transcription level of fitness-related genes lead to the different fitness cost of plasmids carrying different bla subtypes. Fitness of many bla-harboring plasmids enhanced the further dissemination of this gene and increase the risk of bla gene spreading in aquatic environment, and thus further investigation of carbapenem-resistant bacterias among food animals are in urgent need.