Genetic characterization of β-lactam and aminoglycoside resistance genes in Escherichia coli isolates from chickens with suspected colibacillosis

This study aimed to isolate and identify Escherichia coli from chickens with suspected colibacillosis and characterize their antibiotic susceptibility and carriage of β-lactam and aminoglycoside resistance genes. A total of two hundred and fifty (n = 250) samples (blood, spleen, liver and faeces) were collected from chickens with suspected colibacillosis across different poultry farms. Isolates were identified by biochemical and molecular (USP-gene PCR) testing, followed by disk-diffusion susceptibility testing and PCR-based detection of resistance genes. E. coli was recovered and confirmed in 61.2% (153/250) of samples, with the highest proportion, 41.83% (64/153), found in 25–30-day-old chicks, followed by 31–35-day-old chicks at 37.25% (57/153) and 11–15-day-old chicks at 20.91% (32/153). Culture susceptibility testing showed that ciprofloxacin (80.39%, 123/153) had the highest in vitro susceptibility, followed by colistin sulphate (60.13%, 92/153). The highest resistance was observed against cefalexin (87.5%, 134/153), followed by streptomycin (86.27%, 132/153). The aminoglycoside resistance gene aac(6′)-Ib was detected in 13.73% (21/153) of isolates, while among β-lactam resistance genes, bla′TEM was identified in 62.75% (96/153) of isolates, followed by blaCTX-M in 73.86% (113/153) and blaSHV in 31.37% (48/153). E. coli-associated morbidity and mortality have been increasing in young chicks, leading to substantial financial and agricultural losses.