Abstract
The GRAS (generally recognized as safe) status of Enterococcus has not yet been authenticated, but enterococci, as probiotics, have been increasingly applied in human healthcare and animal husbandry, for instance as a dietary supplement, feed additive, or growth promotor. The food chain is the important route for introducing enterococci into the human gut. The pathogenicity of Enterococcus from probiotic products requires investigation. In the study, 110 commercial probiotic products used for human, animal, aquaculture, and plants were examined, among which 36 enterococci were identified, including 31 from Enterococcus faecium, 2 from E. faecalis, 2 from E. casseliflavus, and 1 from E. gallinarum. Strikingly, 28 of the 36 enterococci isolated from probiotics here did not mention the presence of Enterococcus in the labeled ingredients, and no Enterococcus isolates were found from 5 animal probiotics that were labeled with the genus. In total, 35 of the 110 products exhibited hemolysis, including 5 (10.6%) human probiotics, 14 (41.2%) animal probiotics, 8 (57.1%) aquaculture probiotics, and 8 (53.3%) plant probiotics. The detection rates of virulence factors associated with adhesion, antiphagocytosis, exoenzyme, biofilm, and other putative virulence markers (PVM) in 36 enterococci were 94.4%, 91.7%, 5.6%, 94.4% and 8.3%. Twenty-six of the 36 isolated strains exhibited biofilm formation ability, where 25 strains (69.4%) and one (2.8%) were strong and weak biofilm producers, respectively. We analyzed the resistance rates against erythromycin (97%), vancomycin and ciprofloxacin (8%), tetracycline (3%), and high-level aminoglycosides (0%), respectively. High detection rates of msrC/lsaA (86%) and aac(6′)-Ii (86%) were observed, followed by vanC (8%), tetM (3%). The Tn5801-tetM-like integrative conjugative element (ICE) was identified in E. gallinarum, exhibiting resistance to tetracycline (64 μg/mL). Seven probiotic E. faecalis and E. faecium, as active ingredients in human probiotics, shared the same STs (sequence types) and were distinct from the STs of other contaminated or mislabeled enterococci, indicating that two particular STs belonged to native probiotic isolates. These findings advocate appropriate assessments of enterococci when used in probiotics.
Highlights
In the last few years, probiotics have been increasingly used in human, animal, aquaculture, and plant health worldwide
110 probiotic products, including 47 human products used for preventive care and treatment, 34 animal products used for precaution, therapy, food additive, and excreta degradation, aquaculture products used for water purification, and plant products used for biocontrol and growth promotion, were examined
Most of hemolytic isolates belong to E. faecalis and E. faecium, the leading species in enterococcal infections, our results showed that no hemolysis or cytotoxicity was observed for 36 Enterococcus spp., indicating that these Enterococcus isolates were not responsible for the hemolysis activity of the products
Summary
In the last few years, probiotics have been increasingly used in human, animal, aquaculture, and plant health worldwide. Probiotics are applied for healthcare, feed additive growth promotion and so on, but are emerging as novel therapeutic tools for Microorganisms 2021, 9, 726. Enterococci, one kind of LAB, are commensal organisms that are well suited to survival in the gastrointestinal tract of human and animal and environments like water and soil. The emergence and spread of vancomycinresistant Enterococcus (VRE) isolates presents serious therapeutic difficulty, owing to a lack of effective antimicrobial therapy [4]. Quite a few enterococcal strains have been authorized as probiotics for use in pharmaceutical preparations or animal feed additives for decades, such as E. faecium Medilac-Vita (treatment of infantile enteritis, China), E
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