Comparative Analysis between Isolated from Imported and Chinese Native Chicken Breeds.

is considered a significant threat to the global poultry industry and public health. In recent decades, antimicrobial resistance in has attracted increasing concern throughout the world. However, limited information is available on among different breeds of breeder chickens. Thus, this study aimed to compare the prevalence, serotype distribution, emergence of extended-spectrum beta-lactamases (ESBLs), antimicrobial resistance, and genetic resistance mechanisms in among different breeds of breeder chickens. A total of 693 samples (dead embryos, cloacal swabs, water, feed, environmental swabs, and meconium of newly hatched chicks) were selected and cultured for from four breeder chicken farms in Shandong province, China, representing one imported and three native breeds, and the isolates were further serotyped. Of the isolates, susceptibility to 11 antimicrobials of 5 classes, ESBL screening, and the presence of 21 antimicrobial resistance genes were determined in the present study. Overall, 94 (13.6%) isolates were recovered, which were divided into 3 serotypes ( Pullorum ( = 36), Thompson ( = 32), and Enteritidis ( = 26)). The results showed that the prevalence of isolates from the imported breeds was higher compared with the three domestic breeds. Eight of the ninety-four isolates were ESBL-positive strains, which were recovered from a domestic breed chicken farm. These eight ESBL-producing isolates were serotyped to Pullorum. Surprisingly, Enteritidis () and were simultaneously isolated from a single dead embryo observed among one native breed. Meanwhile, among the isolates, 53.2% (50/94) were multidrug-resistant strains, and 44.7% (42/94) of the isolates presented resistance to at least five antibiotics. Nearly all of the isolates (97.9%, 92/94) were resistant to at least one antimicrobial; one isolate of . Thompson was resistant to seven antimicrobial agents belonging to four different classes. The carriage rate of three resistance genes (, , and ) among isolates from the imported breeds (87%, 70%, and 65.2%) was higher than that in those from domestic breeds (35.2%, 36.6, and 14.1%). To our knowledge, this is the first report of ESBLs-producing isolated from a Chinese native breed of breeder chickens. Our results also highlight that a high prevalence of multidrug-resistant contamination is widespread among different breeds of breeder chickens, which is a major risk of food-borne diseases and public health.