# Detection of SXT/R391 integrative conjugative elements carrying tigecycline resistance genes in Shewanella spp. isolated from retail seafood

## TL;DR

This study found tigecycline-resistant Shewanella bacteria in retail seafood, which could spread antibiotic resistance to other bacteria.

## Contribution

First report of SXT/R391 ICEs carrying tigecycline resistance genes in Shewanella strains.

## Key findings

- Shewanella was the most common tigecycline-resistant genus isolated from retail seafood.
- Two Shewanella strains carried the tet(X4) gene, and one co-harbored tmexCD2-toprJ2 and blaNDM-1.
- Tigecycline resistance genes were found on novel SXT/R391 ICEs, which can spread resistance among aquatic bacteria.

## Abstract

Tigecycline is a last resort antibiotic that is used to treat serious infections; however, some bacteria have developed tigecycline resistance by producing a tigecycline-inactivating enzyme or tigecycline resistance efflux pump, encoded by tet(X) and tmexCD-toprJ genes, respectively. Tons of seafood are consumed annually in China; however, whether seafood harbors tigecycline-resistant bacteria is not known. In this study, we isolated various tigecycline-resistant bacteria from retail seafood; among these, Shewanella was the predominant tigecycline-resistant genus (33/76, 43.4%). Genomic sequencing revealed that two Shewanella strains carried the tet(X4) gene, while one Shewanella chilikensis strain co-harbored tmexCD2-toprJ2 and blaNDM-1 genes. The tet(X4) and tmexCD2-toprJ2 were found to be located on novel members of the SXT/R391 family of integrated conjugative elements (ICEs). As per our knowledge, this is the first report on the emergence of SXT/R391 ICEs carrying tet(X4) or tmexCD2-toprJ2 gene in Shewanella strains. The SXT/R391 family ICEs could mediate the spread of tigecycline resistance genes among aquatic bacteria, and contact between seafood and consumers may lead to the dissemination of tigecycline-resistant bacteria. Our study revealed that Shewanella spp. may act as potential reservoirs of tigecycline resistance genes.