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Abstract
Enterococcus durans KLDS6.0930 has previously been shown to have probiotic potential. However, being a potential clinical pathogen, it becomes necessary to evaluate its safety status for novel potential probiotic use. The purpose of this study is to systematically evaluate the safety of E. durans KLDS6.0930 based on its genomics, phenotypic characteristics and oral toxicity. The complete genome of E. durans KLDS6.0930 was sequenced and analyzed for safety-related genes. Antibiotic susceptibility and the production of harmful metabolites were tested. A 28-day repeated oral dose toxicity test was implemented in rats. In vitro, E. durans KLDS6.0930 was resistant to five antibiotics, with intrinsic resistances to four antibiotics and no identified genes for the last. E. durans KLDS6.0930 was not hemolytic and virulence factors were non-functional in its genome. E. durans KLDS6.0930 produced a small amount of tyramine and phenethylamine; genes encoding tyramine decarboxylase were identified. In addition, genotype and phenotype analyses showed that the strain did not have the ability to generate D-lactic acid, indole, or nitroreductase. In vivo, E. durans KLDS6.0930 did not induce adverse effects on the organs, hematological and serum biochemical parameters, or cecal bacterial populations in the oral toxicity test. These results indicate that E. durans KLDS6.0930 can be safely used as a potential probiotic for human consumption and animal feed.
Highlights
Enterococcus, a large genus of lactic acid bacteria (LAB), includes 54 species characterized as grampositive, facultative anaerobic, and non-spore forming (Foulquié Moreno et al, 2006; Van Tyne and Gilmore, 2014)
The average nucleotide identity (ANI) value between the strain KLDS6.0930 and E. durans ATCC6056 was 99.62%. This agrees with the phylogenetic analysis based on 16S rRNA gene sequence (Figure 1A) and the concatenation of 49 ribosomal protein sequences (Figure 1B). These taxonomic results indicated that strain KLDS6.0930 should be assigned to species E. durans
The results showed that E. durans KLDS6.0930 genome and plasmid 1 carry a total of 45 putative virulence factors (Table S1), most of them are cell surface factors associated with host or surface adhesion and promoting biofilm formation
Summary
Enterococcus, a large genus of lactic acid bacteria (LAB), includes 54 species characterized as grampositive, facultative anaerobic, and non-spore forming (Foulquié Moreno et al, 2006; Van Tyne and Gilmore, 2014). Enterococci are long-standing and non-pathogenic commensal bacteria in the gastrointestinal tract (GIT) of humans and animals (Byappanahalli et al, 2012; Weng et al, 2013; Jahan et al, 2015). They are among the first LAB to colonize the neonatal GIT (Fanaro et al, 2003) and could be involved in the development of the human microbiome (DominguezBello et al, 2010). They are frequently used as probiotics to promote human and animal health, or treat diseases such as diarrhea, irritable bowel syndrome, or antibiotic-associated diarrhea (Franz et al, 2011)
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