Abstract
Tetracyclines are important antimicrobial drugs for poultry farming that are actively excreted via feces and urine. Droppings are one of the main components in broiler bedding, which is commonly used as an organic fertilizer. Therefore, bedding becomes an unintended carrier of antimicrobial residues into the environment and may pose a highly significant threat to public health. For this depletion study, 60 broiler chickens were treated with 20% chlortetracycline (CTC) under therapeutic conditions. Concentrations of CTC and 4-epi-CTC were then determined in their droppings. Additionally, this work also aimed to detect the antimicrobial activity of these droppings and the phenotypic susceptibility to tetracycline in E. coli isolates, as well as the presence of tet(A), tet(B), and tet(G) resistance genes. CTC and 4-epi-CTC concentrations that were found ranged from 179.5 to 665.8 µg/kg. Based on these data, the depletion time for chicken droppings was calculated and set at 69 days. All samples presented antimicrobial activity, and a resistance to tetracyclines was found in bacterial strains that were isolated from these samples. Resistance genes tet(A) and tet(B) were also found in these samples.
Highlights
Antimicrobial drugs have a prominent role within the veterinary and animal sciences as they have been used for therapeutic and preventive purposes, and as growth promoters [1]
Analyzing antimicrobials in animal feces is a noninvasive sampling method that allows for the collection of different kinds of information such as the trends on drug use in farms, the spillover of drugs into the environment, the likely ecotoxicological effects of these, and whether or not the possibility for the emergence of resistant bacteria in the digestive tract of domestic animals exists [40]
Regarding the detection of resistance genes, our work shows that when chickens were treated with doses of tetracyclines that followed the recommended therapeutic doses and schedules, these drugs generated a selective pressure on the intestinal microbiota that favored bacteria who were carriers of the tet(A) and tet(B) resistance genes
Summary
Antimicrobial drugs have a prominent role within the veterinary and animal sciences as they have been used for therapeutic and preventive purposes, and as growth promoters [1]. Tetracyclines are the main antimicrobial drugs currently in use for veterinary purposes. Sulfonamides and macrolides are the most common drugs. These classes comprise approximately 90% of all antimicrobials used in the United Kingdom and close to 50% in South Korea [4]. This class of antimicrobials shows bacteriostatic activity against a wide array of Gram-positive and Gram-negative bacteria, mycoplasmas, some mycobacteria, as well as several protozoa and filariae too [5].
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