Bacillus subtilis var. natto increases the resistance of Caenorhabditis elegans to gram-positive bacteria.

AIMS: This study aimed to investigate the effect of Bacillus subtilis var. natto on the susceptibility of the model host, Caenorhabditis elegans, to bacterial infection. METHODS AND RESULTS: Caenorhabditis elegans worms were fed with a standard food consisting of Escherichia coli OP50 strain (control) or B. subtilis (natto) during their larval stage. The worms were then infected with pathogenic bacteria. We analyzed their survival time and RNA sequencing-based transcriptome. Upon infection with Staphylococcus aureus and Enterococcus faecalis, the survival time of B. subtilis (natto)-fed worms was longer than that of the control. Transcriptome analyses showed upregulation of genes associated with innate immunity and defense response to gram-positive bacteria in B. subtilis (natto)-fed worms. CONCLUSIONS: Bacillus subtilis (natto) conferred an increased resistance of C. elegans to gram-positive bacteria. Our findings provided insights into the molecular mechanisms underlying B. subtilis (natto)-regulated host immunity and emphasized its probiotic properties for preventing and alleviating infections caused by gram-positive bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: To the best of our knowledge, this is the first study to show that B. subtilis (natto) confers specific resistance against gram-positive bacteria.