Evaluation of Antibiotic Dissemination into the Environment and Untreated Animals, by Analysis of Oxytetracycline in Poultry Droppings and Litter

Pollution characteristics of heavy metals, antibiotic and antibiotic resistance genes in the crested ibis and their habitat across different lifestyle and geography

Antibacterial resistance in wild animals has been increasingly reported worldwide, even though they are usually not directly exposed to clinically relevant antibiotics. Crested ibis, one of the rarest birds in the world, usually forages in paddy fields and prefer to nest and breed near villages that is greatly influenced by anthropogenic activities. We sampled the feces of crested ibises, as well as their habitat environment samples, to explore the pollution characteristics of heavy metals, antibiotics and antibiotic resistance genes (ARGs). Results showed that the pollution characteristics of heavy metals, antibiotic, ARGs and gut microbiota of crested ibis were more related by host lifestyle and habitats. Captive ibises had higher relative abundances of the total ARGs and tetracycline concentrations compared with feralization and wild ibises, while the heavy metal contents had shown the opposite result. The Characteristics of pollutants in the corresponding environmental samples also exhibited high similarity with the results of fecal samples. The relative abundances of Proteobacteria and Actinobacteria were significantly different between captive and wild individuals, while the abundance of majority bacterial genera was generally higher in wild populations. The concentrations of heavy metals in soil (Cd, Cu and Zn) and water (Cd, Cu, Zn and Cr) were both exceeded the background soil levels or surface water quality standards, suggesting multi-element contamination in the habitat. Ecological risk assessments of soils by Igeo and Er showed that the habitats of wild ibises were heavily and moderately contaminated by Cd, which would possibly pose a threat to the health of ibises. PLS-PM analysis indicated that microbial compositions and residual antibiotics had the most substantial impact on the dynamic changes in ARGs of ibis. Overall, this work provides a comprehensive understanding of the characteristics, risks of those contaminations, and their effects on the ARGs in the habitat of crested ibis.

Assessing the Effect of Oxytetracycline on the Selection of Resistant Escherichia coli in Treated and Untreated Broiler Chickens

Oxytetracycline (OTC) is administered in the poultry industry for the treatment of digestive and respiratory diseases. The use of OTC may contribute to the selection of resistant bacteria in the gastrointestinal tract of birds or in the environment. To determine the effect of OTC on the selection of resistant Escherichia coli strains post-treatment, bacteria were isolated from droppings and litter sampled from untreated and treated birds. Bacterial susceptibility to tetracyclines was determined by the Kirby-Bauer test. A total of 187 resistant isolates were analyzed for the presence of tet(A), (B), (C), (D), (E), and (M) genes by PCR. Fifty-four strains were analyzed by PFGE for subtyping. The proportion of tetracycline-resistant E. coli strains isolated was 42.88%. The susceptibility of the strains was treatment-dependent. A high clonal diversity was observed, with the tet(A) gene being the most prevalent, followed by tet(C). Even at therapeutic doses, there is selection pressure on resistant E. coli strains. The most prevalent resistance genes were tet(A) and tet(C), which could suggest that one of the main mechanisms of resistance of E. coli to tetracyclines is through active efflux pumps.