Assessing the spread of sulfachloropyridazine in poultry environment and its impact on Escherichia coli resistance

Sulfachloropyridazine (SCP) is an antimicrobial (AM) commonly used in the poultry industry. This drug is excreted as the original compound, which may accumulate in litter. This work was done to assess whether SCP residues from droppings of broiler chickens that were treated with therapeutic doses of this drug spread into the production environment and to determine if these events were associated with the selection of resistant bacteria. To this end, broiler chickens were raised under controlled conditions, and their droppings and litter were processed to detect and identify SCP residues using an HPLC-MS/MS technique. This study selected Escherichia coli as an indicator bacterium for AM resistance. Its phenotypic resistance was determined using the Kirby-Bauer disk diffusion method, and its genotypic resistance was determined by performing a conventional PCR test. Our results showed that SCP residues did spread from the treated group to untreated sentinel groups because SCP residues in the litter reached levels up to 43.05 µg·kg⁻¹ in a group placed immediately adjoining to the treated group, while another group placed 30 cm away showed a concentration of 29.79 µg·kg⁻¹. Meanwhile, only trace concentrations were detected in droppings collected from sentinel groups. Of 239 strains of E. coli isolated from droppings, 12.13 % were resistant to sulfonamides, whereas 23.91 % of 92 E. coli isolated from broiler litter were resistant. The most prevalent resistance gene was the sul2 gene, both in droppings and litter, followed by the sul1 gene. The SCP concentrations were associated with the probability of E. coli being resistant to sulfonamides (p-value = 0.01). A Multiple Correspondence Analysis (MCA) also showed that phenotypic and genotypic resistances were associated and that both genes sul1 and sul2 would determine phenotypic resistance to sulfonamides in E. coli. The results presented in this study show that inedible by-products of the poultry industry are potentially a source of drug resistance that can spread from the animal production line to the environment, so awareness of the correct use of antimicrobials is essential to combat antimicrobial resistance.