The characterization and correlation between the phenotypic and genotypic resistance of Campylobacter spp. isolates from commercial broilers and native chickens in the south of Thailand

Chicken is a major reservoir and source of human infections from zoonotic Campylobacter. In southern Thailand, chicken is the most popular meat consumed; however, little is known about the antimicrobial resistance (AMR) of Campylobacter spp. in chicken production systems. We aimed to investigate the prevalence and characteristics of AMR in Campylobacter isolates from commercial broiler and native chicken farms in southern Thailand. A total of 286 Campylobacter isolates (adjusted prevalence: 60.3%, SE +/- 0.01) were recovered, of which 268 were identified as Campylobacter jejuni and 18 as Campylobacter coli. The adjusted prevalence of resistance was highest for nalidixic acid (98.6%), followed by ciprofloxacin (97.2%), enrofloxacin (96.4%), tetracycline (74.6%), tylosin (38.3%), and erythromycin (10.6%). Commercial broilers had resistance levels 7-11% higher to quinolones and 35-47% lower to macrolides and tetracycline (all P <= 0.025) compared to native chickens. Genotypic resistance analyses revealed high prevalence rates (>86%) for gyrA mutant, efflux pump CmeABC, and point mutation A2075G in the 23S rRNA gene. High homogeneity was observed among isolates within study farms. Commercial broilers exhibited higher homogeneity in AMR patterns than native chickens. The best agreement was observed between tetracycline resistance and tet(O) genes (Kappa: k = 0.811, P < 0.001), while the fair agreement was found for quinolone resistance and gyrA mutant genes (k = 0.260-0.271, P < 0.001). No association was detected between macrolide resistance and point mutations in the 23S rRNA gene. These findings fill knowledge gaps on AMR in Campylobacter in Thailand, emphasizing the need for targeted AMR mitigation strategies in both commercial broilers and native chickens. RESEARCH HIGHLIGHTS center dot High Campylobacter prevalence in chickens; C. jejuni more prevalent than C. coli.center dot Susceptibility to macrolides but resistance to quinolones/tetracyclines in isolates.center dot Homogeneous resistance patterns within farms; higher in broilers than in native birds.center dot Partial association between phenotypic and genotypic resistance among isolates.