Occurrence of Florfenicol and Linezolid Resistance and Emergence of optrA Gene in Campylobacter coli Isolates from Tunisian Avian Farms.

Campylobacter species, especially C. coli and C. jejuni, have been associated with a range of human gastrointestinal diseases. During the last two decades, due to the irrational use of antibiotics in poultry farms, high rates of antimicrobial resistance have been globally reported in C. coli and C. jejuni isolates. Recently, acquired linezolid-resistance mechanisms have been reported in Campylobacter spp. isolates, which is a cause of concern to human health. In this study, we performed a retrospective analysis of 139 C. coli isolates previously collected from broilers (n = 41), laying hens (n = 53), eggs (n = 4), and environment (n = 41) to detect acquired genes implicated in linezolid resistance. Isolates were tested for their susceptibility to antimicrobial agents using the Kirby-Bauer disk diffusion assay. Chloramphenicol- and linezolid-resistant isolates were subjected to PCR screening for the following genes: fexA, fexB, floR, RE-cmeABC, cfrA, and optrA. The genetic relatedness of eight multidrug-resistant isolates was determined by multilocus sequence typing (MLST). Among the 139 C. coli isolates, high rates of resistance (57.55%-100%) were detected toward nalidixic acid, ciprofloxacin, erythromycin, azithromycin, ampicillin, chloramphenicol, linezolid, and kanamycin. Among 135 chloramphenicol-resistant isolates, the optrA, cfr, fexA floR, RE-cmeABC, and fexB genes were detected in 124 (124/135, 91.85%), 108 (80%), 105 (77.7%), 64 (47.4%), 56 (41, 48%), and 27 (20%) isolates, respectively. In addition, the majority of isolates harbored more than one of these genes. The selected eight isolates belonged to the same sequence type ST13450, which is a new sequence type (ST), not belonging to ST828 and ST1150 complexes. In conclusion, the emergence of optrA gene in Campylobacter spp. isolates makes this genus an optrA reservoir and vector to other pathogens such as Staphylococcus aureus and Enterococcus spp., which is a cause of concern for human and animal health.