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Published on: January 27, 2019
Probiotic Potential Analysis and Safety Evaluation of Enterococcus durans A8-1 Isolated From a Healthy Chinese Infant
1School of Public Health, Health Science Center, Xi'an Jiaotong University, Xi'an, China.
Insights
Enterococcus durans A8-1, isolated from a healthy infant, exhibits promising probiotic characteristics, including strong adhesion, antimicrobial activity, and anti-inflammatory effects. Safety assessments confirm its low virulence, supporting its potential as a probiotic candidate.
Area of Science:
- Microbiology
- Probiotics
- Gut Health
Background:
- Probiotics offer health benefits but require rigorous safety and efficacy evaluations.
- Enterococcus species are increasingly studied for their probiotic potential.
- Strain-specific characterization is crucial for identifying effective probiotic candidates.
Purpose of the Study:
- To evaluate the probiotic properties and safety of Enterococcus durans isolate A8-1.
- To assess its tolerance, adhesion, antimicrobial activity, and virulence.
- To validate findings through genome resequencing.
Main Methods:
- Phenotypic analysis of acid, bile, and salt tolerance.
- In vitro adhesion assays (mucin, collagen, BSA, Caco-2 cells).
- Biofilm formation, auto-aggregation, and co-aggregation assays.
- Antimicrobial activity testing against pathogenic bacteria.
- Toxin gene detection, hemolysis, and gelatinase assays.
- Antibiotic resistance profiling and Galleria mellonella virulence testing.
- Genome resequencing for genetic characterization.
Main Results:
- E. durans A8-1 demonstrated tolerance to low pH, bile salts, and NaCl.
- High in vitro adhesion, hydrophobicity, and auto-aggregation capabilities were observed.
- The isolate exhibited moderate biofilm production and antimicrobial activity against Gram-positive pathogens.
- A8-1 antagonized Salmonella typhimurium adhesion and reduced inflammation in Caco-2 cells.
- Safety evaluations revealed no hemolytic or gelatinase activity, low G. mellonella virulence, and specific antibiotic resistance profiles.
- Genome sequencing supported phenotypic findings, identifying specific genes related to antibiotic resistance.
Conclusions:
- Enterococcus durans A8-1 possesses significant probiotic characteristics, including robust adhesion, antimicrobial effects, and anti-inflammatory properties.
- The strain demonstrates a favorable safety profile, with low virulence and absence of key virulence factors.
- E. durans A8-1 is a promising candidate for probiotic applications in functional foods and therapeutics.
Abstract:
To evaluate the probiotic characteristics and safety of Enterococcus durans isolate A8-1 from a fecal sample of a healthy Chinese infant, we determined the 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 and interpreted the characters by genome resequencing. Phenotypically, E. durans A8-1 survived at pH 5.0 in 7.0% NaCl and 3% bile salt under aerobic and anaerobic condition. The bacterium had higher adhesion ability toward mucin, collagen, and Bovine Serum Albumin (BSA) in vitro and showed high hydrophobicity (79.2% in chloroform, 49.2% in xylene), auto-aggregation activity (51.7%), and could co-aggregate (66.2%) with Salmonella typhimurium. It had adhesion capability to intestinal epithelial Caco-2 cells (38.74%) with moderate biofilm production and antimicrobial activity against several Gram-positive pathogenic bacteria. A8-1 can antagonize the adhesion of S. typhimurium ATCC14028 on Caco-2 cells to protect the integrity of the cell membrane by detection of lactate dehydrogenase (LDH) and AKP activities. A8-1 also helps the cell relieve the inflammation induced by lipopolysaccharide by reducing the expression of cytokine IL-8 (P = 0.002) and TNF-α (P > 0.05), and increasing the IL-10 (P < 0.001). For the safety evaluation, A8-1 showed no hemolytic activity, no gelatinase activity, and had only asa1 positive in the seven detected virulence genes in polymerase chain reaction (PCR), whereas it was not predicted in the genome sequence. It was susceptible to benzylpenicillin, ampicillin, ciprofloxacin, levofloxacin, moxifloxacin, tigecycline, nitrofurantoin, linezolid, vancomycin, erythromycin, and quinupristin/dalofopine except clindamycin, which was verified by the predicted lasA, lmrB, lmrC, and lmrD genes contributing to the clindamycin resistance. The virulence test of G. mellonella showed that it had toxicity lower than 10% at 1 × 107 CFU. According to the results of these evaluated attributes, E. durans strain A8-1 could be a promising probiotic candidate for applications.
