Prevalence of pathogenic bacteria and their antimicrobial patterns analysis of clinical samples from free-range chickens raised in forest farms in Zhouqu county of Gansu Province, China

The emergence of antimicrobial resistance (AMR) is a global concern, and resistant pathogens such as Escherichia coli (E. coli), Salmonella enterica, and Shigella flexneri are acquired by humans through the food chain. AMR in poultry pathogens threatens both animal and public health, yet data on AMR in free-range systems, particularly forest-farmed chickens in understudied regions like Zhouqu County, China, remain scarce, poorly understood, and hinder targeted interventions. This study investigated bacterial and AMR prevalence in such a chicken-raising system to guide sustainable farming strategies. A total of 1,315 clinical samples, including oropharyngeal swabs (n=280), cloacal swabs (n=355), fresh feces (n=535), and intestinal contents (n=145), were collected from seven free-range farms experiencing severe health issues. Bacterial prevalence and antimicrobial susceptibility profiles were assessed using standardized bacterial culture, the VITEK 2 system, Kirby-Bauer disk diffusion tests, and PCR assays. The most prevalent isolates were E. coli (14.52%), followed by Shigella flexneri (6.54%) and Salmonella enterica (4.94%). Antibiogram analysis revealed that E. coli exhibited (100%) resistance to oxytetracycline, ceftiofur, and ampicillin, with high resistance rates to doxycycline (94.76%), neomycin (85.34%), and tylosin (61.78%). Shigella flexneri showed high resistance to neomycin (66.28%), oxytetracycline (61.63%), and penicillin (58.14%), while Salmonella enterica displayed resistance to neomycin (66.15%) and oxytetracycline (61.54%). Among the isolates, multidrug resistance (MDR) accounted for 27.27% of the total isolates. These findings highlight the high prevalence of AMR among E. coli and Shigella flexneri in free-range poultry farms, posing a critical concern for poultry health, productivity, and food safety. The study underscores the urgent need for stakeholder awareness and intervention strategies to mitigate infectious diseases and curb the emergence and spread of AMR in poultry farming systems.