Abstract
Probiotics have been associated with clinical infections, toxicity, and antimicrobial resistance transfer, raising public concerns. Probiotic enterococci are emerging food risks as opportunistic pathogens, yet little attention has been paid to them. Herein, we collected 88 enterococcal isolates from probiotic products used for humans, companion animals, livestock, and aquaculture. Results showed that all 88 probiotic enterococcal isolates harbored diverse virulence genes, multiple antimicrobial resistance genes, and mobile genetic elements. Notably, 77 isolates were highly resistant to gentamicin. Representative enterococcal isolates exerted toxic activities in both in vitro and in vivo models. Collectively, our findings suggest that probiotic enterococci may be harmful to hosts and pose a potential threat to public health.
Highlights
Probiotics can confer a health benefit on the host when administered in adequate amounts [1], such as activating host immunity [2], improving the function of the intestinal barrier [3], and inhibiting bacterial pathogens [4,5]
We randomly chose four enterococcal isolates, which are recovered from products used for humans (E. faecium 5, Efm5), companion animals (E. faecium 46, Efm46), aquaculture (E. faecium 65, Efm65), and livestock (E. faecium 81, Efm81), respectively, for the following experiments
Our study showed that these enterococci isolated from probiotic products exerted a harmful influence on the host by carrying toxicity, multiple antimicrobial resistance, and mobile genetic elements (MGEs)
Summary
Probiotics can confer a health benefit on the host when administered in adequate amounts [1], such as activating host immunity [2], improving the function of the intestinal barrier [3], and inhibiting bacterial pathogens [4,5]. The occurrence of antimicrobial resistance in some countries has risen to above 90% [6]. This challenge promotes the need for probiotic products as antimicrobial alternatives. Probiotics bear the risks of spreading virulence genes (VGs) and antimicrobial resistance genes (ARGs) [10]. Our previous studies have reported that toxins and mobile ARGs were found in probiotic Bacillus strains [11,12]. A toxin-positive probiotic Bacillus cereus strain has transferred into groundwater and to a nearby fish farm [13]. Risky probiotics could be a reservoir for transferrable VGs and ARGs, and increase the emergence and dissemination of potential harmful factors
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