Occurrence of multidrug resistant/extended spectrum beta-lactamase-producing Escherichia coli isolates belonging to high-risk clones from healthy 1-day-old broiler and layer chicks without in ovo or day-of-hatch antibiotic administration.

This study aimed to investigate the presence of antimicrobial resistant Escherichia coli (E. coli) among healthy day-old broiler and layer chicks in the absence of in ovo or day-of-hatch antibiotic administration. A total of 100 pooled samples from 14 hatcheries across western Algeria were collected for analyses. Antimicrobial susceptibility testing was performed using the disc-diffusion method. Genes encoding antibiotic resistance, integrons, and phylogenetic groups were screened using Polymerase Chain Reaction (PCR), with the genetic relatedness of extended spectrum beta-lactamase (ESBL)-producing isolates determined via multilocus sequence typing. Sixty-eight samples contained E. coli, with high levels of resistance to multiple antibiotics found among broiler (92.10%) and layer chicks (100%) (no significant statistical association, P < 0.05). Multidrug-resistant (MDR)/ESBL-producing isolates were detected in samples from both broiler (n = 11) and layer (n = 2) hatcheries, from which three and five harbored blaCTX-M-1 and blaCTX-M-14, respectively. Additionally, tetA (n = 7), sul1 (n = 5), aac(6´)-Ib-cr (n = 2), and int1 (n = 7) genes were detected. Isolates belonged to the clones ST10 (n = 1), ST617 (n = 1), ST405 (n = 3), ST69 (n = 4), ST224 (n = 3), and ST4494 (n = 1). Study findings indicate that even in the absence of any prior antibiotic administration, day-old chicks in western Algerian hatcheries carry MDR isolates capable of spreading across the national poultry sector, representing a significant public health concern.