Antibiofilm activity of arachidonic acid against linezolid-resistant Enterococcus faecalis: A potential strategy for combating biofilm-related infections.

Enterococcus faecalis, a prevalent opportunistic pathogen, readily forms biofilms on surfaces, contributing to its virulence and antibiotic resistance. Previous studies have highlighted arachidonic acid (AA) as a promising antibiofilm agent. This investigation aimed to elucidate the antibiofilm activity of AA against linezolid-resistant E. faecalis and explore its potential molecular mechanisms. A total of 21 E. faecalis strains were included in this study: the standard strain ATCC 29212 and 20 linezolid-resistant clinical isolates. To determine the minimum inhibitory concentrations (MICs) of antibiotics and AA, the microbroth dilution method was performed. Checkerboard microdilution assays were also performed to assess the interaction between AA and linezolid. The crystal violet method was performed to evaluate the biofilm formation abilities of E. faecalis and the biofilm inhibition activities of different concentrations of AA (0.25 mM, 0.5 mM, and 1 mM). In addition, the expression levels of biofilm-related genes (ebpA, ebpB, ebpC, gelE, ace, atlA, and esp) were measured employing quantitative reverse transcription PCR (qRT-PCR). All clinical strains exhibited resistance to linezolid and tetracycline while remaining susceptible to other antibiotics, including penicillin, ampicillin, vancomycin, teicoplanin, and tigecycline. The MICs of AA against all 21 E. faecalis isolates were >1 mM. Synergy was observed in 75 % of strains (15/20), while additivity was observed in 25 % strains (5/20). All isolates displayed strong biofilm-forming abilities. AA significantly reduced biofilm formation with average inhibition rates of 68.16 %, 69.64 %, and 72.01 % at concentrations of 0.25 mM, 0.5 mM, and 1 mM, respectively (P < 0.001). AA treatment resulted in decreased expression of ebpB, ebpC, ace, and atlA (P < 0.001), while simultaneously increasing gelE expression (P < 0.05). In conclusion, AA exhibited potent inhibitory effects on E. faecalis biofilm formation probably by influencing bacterial adhesion. The addition of AA can restore the susceptibility of linezolid against E. faecalis. These findings suggest that AA may serve as a potential therapeutic agent for preventing and treating E. faecalis infections, particularly those associated with biofilm formation.