Chironomidae larvae: A neglected enricher of antibiotic resistance genes in the food chain of freshwater environments.

Infection caused by pathogenic bacteria carrying antibiotic resistance genes (ARGs) is a serious challenge to human health. Water environment, including water and surface sediments, is an important repository of ARGs, and the activity of aquatic animal can affect the development of ARG pollution in the water environment. Macrobenthic invertebrates are an important component of aquatic ecosystems, and their effects on ARG development in aquatic environments remain unreported. The distribution of ARGs, including tetA gene, sul2 gene, and kan gene, in Chironomidae larvae is demonstrated in this study for the first time. The ARG distribution was related to sampling points, metal elements, and seasons. Animal models demonstrated that Chironomidae larvae enriched ARGs from water and passed them on to downstream predators in the food chain. Conjugative transfer mediated by resistant plasmids was crucial in the spread of ARG in Chironomidae larvae, and upregulated expression of trfAp gene and trbBp gene was the molecular mechanism. Escherichia in Proteobacteria and Flavobacterium in Bacteroidetes, which are gram-negative bacteria in Chironomidae larvae, are the primary host bacteria of ARGs confirmed via resistance screening and DNA sequencing of V4 region of 16S rRNA gene. Feeding experiments further confirmed that ARGs from Chironomidae larvae can be enriched in the fish gut. Research gaps in food chain between sediments and fish are addressed in this study, and Chironomidae larvae is an important enricher of ARGs in the freshwater environment.