Antibiotic resistance gene abundance and bacterial community composition in macroinvertebrates of an urban stream

1. Increase in antibiotic resistance genes (ARGs) in freshwater ecosystems as a consequence of anthropogenic activities is a matter of public health concern. Although researchers have looked at ARG abundance and the factors affecting them in biofilms, water and sediment, the role of freshwater macroinvertebrate gut microbiomes in harbouring and disseminating ARGs is unknown. In the cur- rent study, we tested whether: (a) macroinvertebrate gut microbiomes serve as hotspots of ARGs in comparison to their immediate environment, (b) functional feeding groups (FFGs) impact ARG abundance in macroinvertebrate guts, (c) bacterial community composition and ARG abundance are correlated, and (d) mac- roinvertebrates can be potential vectors of ARGs.2. Macroinvertebrates, sediment and water samples were collected from seven different sites along northeastern Ohio (U.S.A.) streams and abundances of three ARGs (sulI, sulII and tetW) were determined. Bacterial community composition also was examined for respective microbiomes and a microcosm study was de- signed for testing hypothesis 4.3. In many cases, the gut microbiome had higher relative ARG abundance (sulI and sulII) at sites along Tinker's Creek compared to the surrounding substrate and water. ARG abundances along with taxonomic differences in bacterial commu- nity composition were different among the FFGs (ARG abundance higher in om- nivores). Certain bacterial taxa were significantly correlated with one or more ARGs. We did not find that freshwater macroinvertebrates can serve as vectors of ARGs (from the microcosm study).4. Overall, our site- based results suggest that freshwater macroinvertebrate guts may serve as reservoirs of ARGs, differences in ARG abundance among FFGs was possibly a result of differences in bacteria ingested and gut morphophysiological conditions.5. Because this study indicates that macroinvertebrate guts can be potential reservoirs of ARGs, future studies can be designed to understand the role of macroin- vertebrates in dissemination of ARGs in freshwater ecosystems.