Probiotic Lactobacillus and Bifidobacterium strains possess safety characteristics, antiviral activities and host adherence factors revealed by genome mining

Background: Probiotics belonging to Lactobacillus and Bifidobacterium spp. have been exploited for their health benefits in treatment and prevention of many pathological conditions and promoting human health. Recent advances in understanding probiotics-human interaction through microbiome research in the context of various medical conditions suggest their provisional role in preventive, personalized, and predictive medicine. To streamline their application in disease prevention, development of personalized-based treatments, or their use as biomarkers for predictive diagnosis, in vitro screening for strains with potential probiotic properties should be performed. In this work, we aimed to emphasize the probiotic features of four Lactobacillus and two Bifidobacterium probiotic strains which showed antagonistic properties against microbial pathogens. Methods: Firstly, cytotoxicity assessment of cell-free preparations from these strains was performed using a baby hamster kidney (BHK) cells and cell viability was measured by means of sulfo-rhodamine B stain. Secondly, Newcastle disease (ND) and infectious bursal disease (IBD) viruses which pose a great threat in infected poultry were used for assessing antiviral activity of probiotics. Thirdly, the genomes of six probiotic strains were used to identify genes encoding host adherence factors that mediate interaction with human tissues. Results: Probiotic preparations exhibited insignificant toxicity as indicated by the high survival rate of BHK cells (surviving fraction varied from 0.82 to 0.99) as compared to the untreated control. Cell-free preparations of probiotics mixed with equal volume of ND and IBD viruses (106 and 104 Tissue Culture Infectious Dose 50, respectively) reduced the titer of ND and IBD viruses on chicken embryo fibroblast cells. Genome mining analysis revealed that the draft genomes of these strains were predicted to encode LPXTG-containing proteins, surface layer proteins, tight adherence pili, sortase-dependent pili, fibronectin, or collagen binding proteins and other factors that adhere to human tissues such as mucus. Such adherence factors enable probiotic bacteria to interact and colonize the host. Conclusion: Taken together, safety privileges, antiviral activities, and genomically encoded host interaction factors confirmed probiotic features of the six probiotic strains and their potential in promoting human health.