The phenomenon of bacterial resistance is a well-known and well-researched phenomenon and is a global issue of concern. Therefore, we studied the production and mechanism of drug resistance of Enterococcus faecalis from water sources to ciprofloxacin, oxytetracycline, and ampicillin, following nitrogen and phosphorus eutrophication. We established microcosms to explore how nitrogen and phosphorus eutrophication affects (i) E. faecalis drug resistance, (ii) E. faecalis biofilm formation and adhesion ability; and (iii) the expression levels of the E. faecalis fsrA regulatory gene and the downstream gelatinase gene gelE. The results revealed that all the obtained isolates had biofilm formation ability, and almost all had fsrA and gelE gene expression. In addition, E. faecalis gelE expression was significantly enhanced in the experimental group. We used crystal violet staining to observe the process of biofilm enhancement in the growing phase of strains. In conclusion, E. faecalis resistance to ciprofloxacin, oxytetracycline, and ampicillin was related to biofilm formation. Furthermore, the high resistance level of E. faecalis showed a relationship with the expression of the fsrA and gelE genes.

Keywords: Enterococcus faecalis, drug resistance, fsrA, gelE