Postbiotics of the Lactiplantibacillus plantarum EIR/IF-1 Strain Show Antimicrobial Activity against Oral Microorganisms with pH Adaptation Capability

Postbiotics offer better properties than probiotics. This study investigated the antimicrobial activity of Lactiplantibacillus plantarum EIR/IF-1 postbiotics against pH-adaptive bacteria, namely Prevotella denticola, Fusobacterium nucleatum, and Streptococcus sanguinis. Cell-free culture media of L. plantarum EIR/IF-1 were used as postbiotics in either crude (acidic) or neutralized form to also understand non-pH-dependent antimicrobial potential. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and viable cell counts were determined for crude and neutralized postbiotics. Culture media adjusted to different pH values were also compared to adjusted media with postbiotics to understand the strength of organic acids in postbiotics. Antibiofilm activity of postbiotics was determined against polymicrobial biofilm formation. Finally, the toxicity of crude postbiotics was tested on human periodontal ligament fibroblast cells (hPDLFCs). MIC values of crude postbiotics were 12.5 mg/mL for all strains. F. nucleatum and P. denticola strains were sensitive to neutralized postbiotics after 48 h of incubation. Moreover, 12.5 and 25 mg/mL postbiotics inhibited biofilm formation and 2.5 mg/mL and lower concentrations of crude postbiotics showed no cytotoxicity in hPDLFCs. This study showed that postbiotics have antimicrobial activity against pH-adaptive oral bacteria and no cytotoxic effect on hPDLFCs depending on the dose. The non-acidic antimicrobial components of postbiotics could also enable their safe use in the oral cavity.