Heat-killed Lactobacillus acidophilus mediates Fusobacterium nucleatum induced pro-inflammatory responses in epithelial cells

Probiotics is widespreadly used nowadays. However, the safety issue with the use of live probiotics is still a matter of contention. In recent years, an expanding body of evidence supports the beneficial role of heat-killed probiotics in the maintenance of systemic health, whereas the role of these heat-killed bacteria on periodontal health remains unclear. This study aimed to evaluate the effects of heat-killed probiotics on periodontal pathogen virulence and associated mechanisms. We demonstrated that heat-killed Lactobacillus acidophilus was able to coaggregate with Fusobacterium nucleatum, the bridging bacteria of oral biofilm, and inhibit the adhesion and invasion of F. nucleatum, leading to a subsequent elimination of pro-inflammatory cytokine production in oral epithelial cells. This coaggregation further caused a suppression of the virulence gene fap2 expression in F. nucleatum. Therefore, heat-killed L. acidophilus might downregulate the pro-inflammatory cytokine expression in epithelial cells via coaggregation with F. nucleatum and suppression of F. nucleatum fap2 expression, which was the first demonstration that heat-killed probiotics modulate periodontal disease pathogenesis via coaggregation. Collectively, this finding provides new evidence that heat-killed probiotics might exert beneficial effects to periodontal health by coaggregating with periodontal pathogens and modulating their virulence.