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Probiotic and Safety Properties Screening of Enterococcus faecalis from Healthy Chinese Infants
Juan Wang1, Rong Da2, Xiaohong Tuo1
1School of Public Health, Xi'an Jiaotong University Health Science Center, P.O.44, NO.76 Yanta West Road, Xi'an, 710061, Shaanxi, China.
Insights
Seven *Enterococcus faecalis* infant isolates show probiotic potential. Strain A3-1 demonstrated superior adhesion, antibacterial activity, and biofilm formation, with low virulence, suggesting it could be a promising probiotic candidate.
Area of Science:
- Microbiology
- Probiotics
- Food Science
Background:
- *Enterococcus faecalis* is found in the gut microbiota of healthy infants.
- Probiotic bacteria offer health benefits but require rigorous safety and efficacy evaluation.
- Identifying novel probiotic strains from infant gut microbiota is crucial for developing targeted health interventions.
Purpose of the Study:
- To assess the probiotic properties and safety of seven *Enterococcus faecalis* strains isolated from healthy Chinese infants.
- To evaluate their tolerance to gastrointestinal conditions, adhesion capabilities, antimicrobial effects, and virulence factors.
- To determine their potential for development as a probiotic formulation.
Main Methods:
- *In vitro* assays evaluated tolerance to low pH, bile salts, and NaCl.
- Adhesion to Caco-2 cells and biofilm formation were assessed.
- Antimicrobial activity, toxin gene presence, hemolysis, gelatinase activity, and antibiotic resistance were determined.
- Virulence was tested using *Galleria mellonella* model.
Main Results:
- All seven strains exhibited tolerance to simulated gastric conditions (pH 5.0, 3% bile salt, 7.0% NaCl) and adhered to Caco-2 cells (>10%).
- Strain A3-1 showed enhanced mucin, collagen, and BSA adhesion, potent antibacterial activity, and robust biofilm production.
- While all strains were gamma-hemolytic and carried virulence genes (e.g., *asa1*, *esp*, *agg*), most exhibited low toxicity in the *G. mellonella* model.
- All isolates were susceptible to common antibiotics like vancomycin and linezolid but resistant to erythromycin.
Conclusions:
- The evaluated *Enterococcus faecalis* infant isolates possess significant probiotic characteristics, including tolerance to gastrointestinal conditions and adhesion capabilities.
- Strain A3-1 emerged as a promising candidate for probiotic development due to its superior functional properties and low virulence.
- Further research should focus on *in vivo* studies to confirm the safety and efficacy of A3-1 for potential application in functional foods or supplements.
Abstract:
The aim of this study was to evaluate the probiotic characteristics and safety of seven Enterococcus faecalis isolates from fecal samples of healthy Chinese infants. We evaluated the isolates' tolerance to low pH, survival in bile salts and NaCl, adhesion ability, biofilm formation, antimicrobial activity, toxin gene distribution, hemolysis, gelatinase activity, antibiotic resistance, and virulence to Galleria mellonella. All strains survived at pH 5.0, in 7.0% NaCl, and in 3% bile salt. Adhesion to Caco-2 cells was above 10%. Strain A3-1 had higher adhesion ability toward mucin, collagen, and BSA in vitro, better antibacterial activity, and the strongest biofilm production. We detected seven virulence genes with a distribution of asa1 (100%), cylA (71.4%), esp (85.7%), hyl (14.3%), gelE (85.7%), ace (42.9%), and agg (71.4%). Although all strains were γ-hemolytic, none showed gelatinase activity based on physiological activity detection. All isolates were susceptible to benzylpenicillin, ampicillin, ciprofloxacin, levofloxacin, moxifloxacin, tigecycline, nitrofurantoin, linezolid, and vancomycin; they were not susceptible to erythromycin, quinupristin/dalofopine, and clindamycin. The virulence test of G. mellonella showed that, except for strains 106-1 and 113-1, the other strains had toxicity lower than 10%. Strain A3-1 may have the greatest potential to be developed as a probiotic.
