Field-realistic dose of cefotaxime enhances potential mobility of O-lactam resistance genes in the gut microbiota of zebrafish (Danio rerio)

With large amounts of cephalosporin end up in natural ecosystems, water has been acknowledged as the large reservoir of O-lactam resistance over the past decades. However, there is still insufficient knowledge available on the function of the living organisms to the transmission of antibiotic resistance. For this reason, in this study, using adult zebrafish (Danio rerio) as animal model, exposing them to environmentally relevant dose of cefo-taxime for 150 days, we asked whether cefotaxime contamination accelerated O-lactam resistance in gut microbiota as well as its potential transmission. Results showed that some of O-lactam resistance genes (ORGs) were intrinsic embedded in intestinal microbiome of zebrafish even without antibiotic stressor. Across cefo-taxime treatment, the abundance of most ORGs in fish gut microbiome decreased apparently in the short term firstly, and then increased with the prolonged exposure, forming distinctly divergent ORG profiles with antibiotic -untreated zebrafish. Meanwhile, with the rising concentration of cefotaxime, the range of ORGs' host-taxa expanded and the co-occurrence relationships of mobile genetics elements (MGEs) with ORGs intensified, indi-cating the enhancement of ORGs' mobility in gut microbiome when the fish suffered from cefotaxime contam-ination. Furthermore, the path of partial least squares path modeling (PLS-PM) gave an integral assessment on the specific causality of cefotaxime treatment to ORG profiles, showing that cefotaxime-mediated ORGs variation was most ascribed to the alteration of MGEs under cefotaxime stress, followed by bacterial community, func-tioning both direct influence as ORG-hosts and indirect effects via affecting MGEs. Finally, pathogenic bacteria Aeromonas was identified as the critical host for multiple ORGs in fish guts, and its O-lactam resistance increased over the duration time of cefotaxime exposure, suggesting the potential spreading risks for the antibiotic -resistant pathogens from environmental ecosystems to clinic. Overall, our finding emphasized cefotaxime contamination in aquatic surroundings could enhance the O-lactam resistance and its transmission mobility in fish bodies.