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

species, especially and , 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 and isolates. Recently, acquired linezolid-resistance mechanisms have been reported in spp. isolates, which is a cause of concern to human health. In this study, we performed a retrospective analysis of 139 isolates previously collected from broilers ( = 41), laying hens ( = 53), eggs ( = 4), and environment ( = 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: , , , RE-, , and . The genetic relatedness of eight multidrug-resistant isolates was determined by multilocus sequence typing (MLST). Among the 139 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 , , , RE-, and 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 gene in spp. isolates makes this genus an reservoir and vector to other pathogens such as and spp., which is a cause of concern for human and animal health.