# Identification of the Phenicol Efflux Gene fexB and Its Co‐Occurrence With the Oxazolidinone/Phenicol Resistance Gene optrA in Avian Campylobacter jejuni Isolates From Tunisia

## TL;DR

This study identifies a new resistance gene in a bird-related bacteria in Tunisia and shows it often appears with another resistance gene, raising concerns about antibiotic resistance spread.

## Contribution

First report of the fexB gene and its co-occurrence with optrA in Campylobacter jejuni.

## Key findings

- High prevalence of multidrug resistance in avian C. jejuni isolates from Tunisia.
- fexB and optrA were frequently co-occurring in resistant isolates.
- Tunisian fexB and optrA sequences were closely related to those in Enterococcus spp., suggesting gene transfer between species.

## Abstract

Campylobacter jejuni, a major foodborne and zoonotic pathogen linked to poultry, is showing rising resistance to last‐resort antimicrobials like oxazolidinones and phenicols. Such resistance threatens both animal and human health. Its ability to acquire genes from gram‐positive bacteria highlights the need for surveillance in avian reservoirs.

This study aimed to characterize oxazolidinone‐ and phenicol‐resistance determinants among 197 C. jejuni isolates from avian sources in Tunisia.

Isolates were studied by determining their antimicrobial susceptibility by disk diffusion method, and resistant isolates were screened by PCR for fexA, fexB, floR, RE‐cmeABC, cfr, and optrA genes.

Resistance rates were alarmingly high (57.6%–100%) across multiple antibiotic classes, and the majority were multidrug resistant. Among 155 (78.7%) chloramphenicol‐resistant isolates, the prevalence of optrA, cfr, fexA, floR, RE‐cmeABC, and fexB was 85%, 55%, 75%, 46%, 42%, and 22%, respectively, with most isolates harboring multiple genes. Phylogenetic analysis revealed close relatedness among Tunisian optrA and fexB sequences and similarities with those reported in Enterococcus spp., suggesting intergenus gene exchange.

This study reports for the first time the detection of fexB gene and its co‐occurrence with optrA in C. jejuni, highlighting its potential role as a reservoir of transferable resistance genes. These findings underscore the urgent need for enhanced surveillance and antimicrobial stewardship within a One Health framework.