The presence of ciprofloxacin (CIP) residues in aquatic environments may induce antibiotic resistance in tilapia and alter the diversity of their gut microbiota, highlighting the critical importance of understanding the risks associated with antibiotic contamination. The aim of this study was to investigate the impact of CIP on the development of quinolone resistance and microflora in the tilapia gut. For these studies, high‐throughput next‐generation sequencing of 16S rRNA, PCR, real‐time PCR, and standard microbiologic culture methods was utilized. Our findings revealed a significant increase in the relative abundance of plasmid‐mediated quinolone resistance (PMQR) genes in all the treatment groups (10, 1, and 0.1 milligrams per liter mg/L CIP) after 7 or 14 days, compared to the control group ( p < 0.05), with the exception of the qnrA gene in the 0.1 mg/L group. Moreover, a marked rise in CIP‐resistant (CIPr) Enterobacteriaceae and Aeromonas spp. was observed in all treatment groups relative to the control, peaking in the 1 mg/L group at day 35 ( p < 0.05), and the Aeromonas spp. isolated from 10 mg/L group were detected as the largest number of double quinolone resistance‐determining region (QRDR) mutations. Regarding the gut microbiome, the population of Fusobacteria was increased, while the Proteobacteria, Bacteroidetes, and Firmicutes declined in all groups. Species diversity significantly decreased in the 10 mg/L and 1 mg/L groups compared to the 0.1 mg/L and control groups. While 10 mg/L and 1 mg/L CIP significantly altered the gut microbiome and enriched PMQR genes, the effects at 0.1 mg/L were more subtle—with increased PMQR gene abundance observed for some genes (e.g., qnrB and qnrS ) but not others ( qnrA ). This suggests that even low‐level antibiotic residues can exert selective pressure, though the magnitude of effect is concentration‐dependent.
Hou et al. (Thu,) studied this question.