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.

BACKGROUND

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.

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

METHODS

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.

RESULTS

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.

CONCLUSION

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.