Biological characteristics of bacteriocin-producing Enterococcus faecium F11.1G

Abstract:

[Background] The abuse of antibiotics leads to increasingly severe drug resistance, which poses a growing threat to animal health and the environment. In response to this global public health threat, many countries have banned the use of antibiotics as food and feed additives. In this context, probiotics emerge as alternatives. [Objective] To comprehensively characterize bacteriocin-producing Enterococcus faecium F11.1G. [Methods] Tests were carried out to examine the thermal stability, acid tolerance, bile salt tolerance, antibiotic sensitivity, surface hydrophobicity, self-aggregation, and protease resistance of this strain. [Results] The fermentation supernatant of E.faecium F11.1G had strong thermal stability and maintained antibacterial activity at 110 ℃, with an optimal growth temperature of 37 ℃. The strain grew well and had the highest survival rate at pH 5.9. As the pH decreased, the growth was inhibited. However, at pH 1.8, the strain can still grow with a survival rate of 9%. The strain showed the survival rates of 140.0%, 126.6%, and 96.6% at the bile salt concentrations of 0.10%, 0.15%, and 0.20%, respectively. The strain was tolerant to 16 antibiotics: cefepime, amikacin, gentamicin, norfloxacin, erythromycin, roxithromycin, polymyxin B, lincomycin, streptomycin, neomycin, metronidazole, clindamycin, nystatin, trimethoprim, azithromycin, and kanamycin. It was moderately sensitive to ceftazidime, levofloxacin, and ciprofloxacin and highly sensitive to penicillin, cefazolin, cefuroxime, chloramphenicol, tetracycline, doxycycline, teicoplanin, clarithromycin and nitrofurantoin. The hydrophobicity of E.faecalis F11.1G to hexane, xylene, ethyl acetate, and dichloromethane was 84.29%, 25.75%, 31.26%, and 15.08%, respectively. The self-aggregation rates of E.faecalis F11.1G at the time points of 3, 6, 9, 12, 15, and 18 h were 51%, 54%, 76%, 80%, 83%, and 84%, respectively. In the presence of protease K, the inhibitory effects of the strain against Escherichia coli and Salmonella were significantly weakened, with the inhibition zone diameters of 13.05 mm and 11.28 mm and the inhibition rate decreases of 52% and 58%, respectively. In the presence of trypsin and pepsin, no inhibition zone was formed, which indicated that the strain almost completely lost the antibacterial effects. [Conclusion] E.faecium F11.1G demonstrates strong tolerance to high temperatures, acids, and bile salt, resistance to 16 antibiotics, high hydrophobicity to hexane, and high self-aggregation. However, it loses its antibacterial activity after treatment with trypsin and pepsin, which indicates that the antibacterial substance is a protein or peptide. The results provide basic data for the safe application of probiotics.