Investigating the effect of an oxytetracycline treatment on the gut microbiome and antimicrobial resistance gene dynamics in Nile tilapia (Oreochromis niloticus). The impact of oxytetracycline on the gut microbiome and antimicrobial resistance in Nile tilapia

Antibiotics play a vital role in aquaculture where they are commonly used to treat bacterial dis-eases. However, the impact of antibiotic treatment on the gut microbiome and development of an-timicrobial resistance in Nile tilapia (Oreochromis niloticus) over time, remains to be fully under-stood. In this study, fish were fed a single treatment of oxytetracycline (100 mg kg bodyweight-1) for eight days, followed by a 14-day withdrawal period. Changes in the distal gut microbiome were measured using 16S rRNA sequencing. In addition, the abundance of antimicrobial re-sistance genes was quantified using real-time qPCR methods. Overall, the gut microbiome com-munity diversity and structure of Nile tilapia was resilient to oxytetracycline treatment. Howev-er, antibiotic treatment was associated with an enrichment in Plesiomonas, accompanied by a de-cline in other bacteria taxa. Oxytetracycline treatment increased the proportion of tetA in the dis-tal gut of fish and tank biofilms in the OTC-group. Furthermore, the abundance of tetA along with other tetracycline resistance genes was strongly correlated with a number of microbiome mem-bers, including Plesiomonas. Findings from this study demonstrate that antibiotic treatment can exert selective pressures on the gut microbiome of fish, in favour of resistant populations which may have long-term impacts on fish health.