Colibacillosis in broiler chicks and its etiological link to the biological characteristics of Escherichia coli isolates from the breeder flock

Pathogenic strains of Escherichia coli, capable of causing avian colibacillosis (APEC), currently pose a significant threat to modern poultry farming, in particular industrial broiler production. Moreover, the origin of colibacillosis in broiler chickens is connected with parental health issues. Therefore, the aim of the work was to investigate the etiological link between colibacillosis in 1-day old chicks and the biological characteristics of E. coli isolates from the breeder flock. A total of 65 pathogenic E. coli isolates were detected from broiler-breeders (n = 14) and 1-day-old chikens (n = 51). This shows a huge impact of collibacillosis on poultry farming at different levels of production. The main lesions were associated with fibrin deposition and omphlaitis formation. The last-mentioned parameter could affect the viability of chicks; nevertheless, the average Pasgar score was identified as 9.7 points. Amomg APEC, the most prevalent were O78 and O18 serotypes, wich were characterized by the absence of β-hemolysis. Moreover, the antibiotic profile of APEC isolated from parenteral and progeny flocks was similar. A high level of resistance to amoxicillin, amoxiclav, doxycycline, tetracycline, and enrofloxacin was found; more than 70% of isolated APEC were invulnerable to the mentioned antimicrobials. The most effective antibiotics were colistin, gentamicin, and florfenicol, to which only 0.0% and 2.0%, 14.3 and 9.8%, 7.1% and 2.0% of isolated APEC from broiler-breeders and chickens, respectively, were resistant. In addition, prolonged treatment of birds led to the formation of multi-resistant strains that affected chickens from the first days of life. Thus, studying the process of APEC infection through an integrated production chain can be useful for taking appropriate measures to prevent early cases of colibacilosis.