Foodborne diseases have been witnessing a constant rising trend worldwide, mainly caused by pathogenic microorganisms, such as Bacillus spp., posing a direct threat to public health. The purpose of this study was to evaluate the biological risk of foodborne and probiotic Bacillus spp. in Beijing markets. A total of 55 Bacillus isolates, including 29 B. cereus, 9 B. licheniformis and 7 B. subtilis, mostly found in dairy products (32.7%), were recovered from 106 samples and identified by matrix-assisted laser desorption/ionization mass spectrometry and polymerase chain reaction methods. The susceptibility towards 16 antibiotics was determined using a broth microdilution method. Bacillus showed a high level of resistance to florfenicol (100%), lincomycin (100%), tiamulin (78.2%) and ampicillin (67.3%), while they were all susceptible or intermediate to vancomycin and rifampin. Additionally, we obtained the whole genome of 19 Bacillus strains using high-throughput sequencing, and the rates of resistance genes van, fosB, erm and tet were 57.9%, 57.9%, 21.1% and 26.3%, respectively. Moreover, 100%, 9.1%, 45.5% and 100% of these isolates carried virulence genes nhe, hbl, cytK and entFM, respectively. Lastly, 60% Bacillus strains were positive in hemolysis tests, and 3 B. licheniformis strains displayed an inhibitory activity on the growth of S. aureus ATCC 29213 using agar overlay technique. Our study outlines the characteristics of foodborne Bacillus spp. and provides information for the monitoring of food safety.

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.

Gastrointestinal infection is a leading cause of gut diseases attracting global health concerns. The emerging antimicrobial resistance in enteric pathogens drives the search of viable and renewable alternatives to antibiotics for the health of both human beings and animals. Spore-forming probiotic Bacillus have received extensively interests for their multiple health benefits, including the restoration of microbiota dysbiosis and the reduction of drug-resistant pathogens. These promising benefits are mainly attributed to the activity of structurally diverse Bacillus-derived metabolites, such as antibacterial compounds, short-chain fatty acids, and other small molecules. Such metabolites show the capacity to directly target either the individual or community of bacterial pathogens, and to potentiate both host cells and gut microbiota. The better understanding of the mechanisms by which probiotic Bacillus and the metabolites modulate the metabolism of hosts and microbiota will advance the screening and development of probiotic Bacillus. In this review, we discuss the interaction among probiotic Bacillus, microbiota and host, and summarize the Bacillus-derived metabolites that act as key players in such interactions, shedding light on the mechanistic understanding of probiotic Bacillus against enteric bacterial infections.