Dietary exposure to sulfamethazine alters fish intestinal homeostasis and promotes resistance gene transfer

The present study was undertaken to explore the effects of sulfamethazine (SMZ) dietary exposure on the enrichment of the intestine microbial structure, and antibiotic resistance gene (ARGs) transmission in marine medaka, with respect to antibiotic dose, duration, and sex. In male fish, a dietary exposure of 10 mu g/L SMZ led to a heightened SMZ enrichment in the intestine, whereas metabolite (N-SMZ) levels were elevated at a higher exposure concentration (100 mu g/L). Conversely, female fish exhibited stable levels of accumulation and metabolic rates across the exposure period. The composition of intestinal microorganisms revealed that exposure duration exerted a greater impact on the abundance and diversity of gut microbes, and microbial responses to SMZ varied across exposure time points. The expansion of Bacteroidetes and Ruegeria likely stimulated SMZ metabolism and contributed to the more balanced level of SMZ and N-SMZ observed in females. In males, shortterm SMZ stress resulted in a disruption of intestinal homeostasis, while the rise in the abundance of the Fusobacteria and Propionigeniuma suggested a potential enhancement in intestinal anti-inflammatory capacity over time. Overall, female medaka exhibited greater adaptability to SMZ, and males appear to experience prolonged effects due to SMZ. A total of 11 ARGs and 5 mobile genetic elements (MGEs) were identified. Ruegeria is the main carrier of two types of MGEs (IS1247, ISSm2-Xanthob), and may serve as an indicator of ARG transmission. Therefore, it is rational to consider some fish breeding areas in natural waters as potential reservoirs of antibiotic resistance. This research will provide a valuable reference for the transmission of drug resistance along the food chain.

Automated summary

This study explores the effects of sulfamethazine (SMZ) dietary exposure on the enrichment of intestinal microbial structure and antibiotic resistance gene (ARGs) transmission in marine medaka. The results show that the exposure dose, duration, and sex have different impacts on SMZ enrichment in the intestine. Female medaka exhibit greater adaptability to SMZ, while males may experience prolonged effects. The study also identifies changes in the composition of intestinal microorganisms and the transmission of ARGs.