Pollution characteristics of livestock faeces and the key driver of the spread of antibiotic resistance genes

The increasing prevalence of antibiotic resistance genes (ARGs) in livestock and poultry faeces has attracted considerable amounts of attention. However, in the actual breeding environment, the key driver of the spread of ARGs and which bacteria are involved remain unclear. This study investigated 19 antibiotics and 4 heavy metals in 147 animal faeces. The results showed that piglet faeces exhibited the highest levels of antibiotics and heavy metals. Twelve ARGs, 4 mobile genetic elements (MGEs) and bacterial communities of piglet faeces from 6 pig farms were further assessed to determine the key driver and relevant mechanism of the spread of ARGs. Sulphonamides (SAs) explained 36.5% of the variance (P < 0.05) of the bacterial community and were significantly related to 8 genes (P < 0.01), indicating that SAs dominated the spread of ARGs and should be tightly supervised. Structural equation modelling (SEM) indicated that SAs increased the abundance of ARGs via two pathways: horizontal transfer of ARGs (involving 10 genera) and vertical transfer of ARGs (involving 26 genera). These results improve our understanding of the potential hosts involved in the spread of ARGs, suggesting that monitoring of the above potential hosts is also important in animal feeding practice.