Occurrence and fate of antibiotic resistance genes and their potential hosts during anaerobic fermentation of napier grass silage with the addition of different lactic acid bacteria

Silage, as the primary forage for ruminants, could serve as a reservoir for antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs). These genes gained access to the animals' systems via host bacteria, causing a latent health risk. This study aimed to investigate the fate and transmission mechanism of ARGs in napier grass silage treated with either Lactiplantibacillus plantarum (LP) or Enterococcus faecalis (E). The results indicated that Ensilied storage could effectively reduce ARGs abundance. Concurrently, bacterial community exhibited obviously difference by different treatments in silage. Firmicutes and Protebacteria could be the potential hosts, which were high abundance before and after ensiling. The abundance of ermB and Tn916/145 in the E group was the lowest in the fermented process. The inoculation of LP and E effectively down-regulated the expression of qnrD after 30 days fermentation, and also significantly decreased the bacteria of positive correlation with this gene, such as Pantoea_sp_PSNIH1, Pseudomonas_psychrotolerans and Pantoea_ananatis_PA13. The LP remain inhibiting effect to the expression of sul1 during ensiling, compared with the CK group. In conclusion, adding LP or E could markedly improve fermentation quality of napier grass silage and decrease some ARGs and MGEs. The decline in ARGs and MGEs was linked to a decrease in harmful bacterial populations.