Antibiotic-contaminated effluent promotes mobile resistance in environmental bacterial communities

The high and sometimes inappropriate use of antibiotics has accelerated the development of antibiotic resistance, creating a major challenge for the sustainable treatment of infections world-wide. Bacteria often respond to antibiotic selection pressure by acquiring resistance genes, i.e. mobile genetic elements that can be shared horizontally between species. Environmental microbial communities maintain diverse collections of resistance genes, which can be mobilized into pathogenic bacteria. Recently, exceptional environmental releases of antibiotics have been documented, but the effects on the promotion of resistance genes and the potential for horizontal gene transfer have yet received little attention. Using metagenomic sequencing we here show high levels of multiple classes of resistance genes in river sediments exposed to waste water from the production of antibiotics in India. Our analysis also revealed a high prevalence of integrons, transposons and plasmids, further emphasizing the risks for horizontal gene transfer. The results suggest that antibiotic contamination may play a role in the promotion of resistance genes and their mobilization from environmental microbes to other species and eventually to clinically relevant bacteria. The entire life-cycle of antibiotic substances, both before, under and after usage, should therefore be considered to fully evaluate their role in the promotion of resistance.