The mobile tigecycline resistance gene tet(X4) persists along with the animal manure treatment process and fertilizer receiving soil

The emergence of plasmid-mediated high-level tigecycline-resistant genes [tet(X3) to tet(X6)] in animals and human clinics raised serious concerns over their possible cross-environmental dissemination. Here, we explored the environmental behavior of these emerging mobile tet(X)-variant genes in typical manure treatment processes and amended soils based on a large-scale molecular investigation across eight Chinese provinces. tet(X4) was the predominant mobile tet(X)-variant gene in fresh manures, natural or thermophilic composting products, and corresponding amended soils with the highest detection rates and absolute abundance. The occurrence of mobile tet(X)-variant genes, particularly tet(X4) in receiving soils following the application of the composting fertilizers provided the evidence for the transmission from animal manures to soils. Although thermophilic composting was found to exhibit higher efficacies in total tet(X)-variant genes removal via paired-sampling strategy, the tet(X4) gene had the poorest reduction (94.1%) compared with the other mobile tet(X)-variant genes. This could attribute to the existence of potential thermotolerant bacterial hosts (Flavobacterium and Sphingobacterium) and active horizontal gene transfer of tet(X4). The tet(X4) gene showed better potential to persist and could be proposed to play an indicator of fate and dissemination risk of tet(X)-variant genes in livestock related environments.