Effect of SCFAs on Attachment and Biofilm of Actinomyces oris

Objectives: The Gram-positive bacterium Actinomyces oris is known as one of initial colonizers on the tooth surface. Recently, we reported that butyric acid, one of short-chain fatty acids (SCFAs) promotes GroEL-dependent oral biofilm and initial attachment of A. naeslundii, which is another genotype to A. oris. However, effects of SCFAs on the oral biofilm formation of A. oris are poorly understood. In this study, we investigated the effects of SCFAs on the biofilm formation of A. oris.
Methods: Biofilm formations of A. oris NG4 and NG4.ΔfimA, which is deficient mutant of shaft fimbrillin FimA, on the human saliva-coated 96 well microtiter plate were observed in TSB with 0.25% (w/v) sucrose supplemented with 6.25 mM SCFAs. Biofilms were stained by 0.5% safranin and observed by the absorbance at 492 nm. Initial attachment assay, A. oris NG4 wild type and NG4.ΔfimA
were applied on the 6 well culture plates, incubated for 1 hour in TSB with sucrose with 60 mM SCFAs, and observed by Live/Dead staining kit and confocal lazar microscope.
Results: Biofilm formations of A. oris NG4 were inhibited by addition of butyric, formic and valeric acids but not affected by acetic, lactic and propionic acids, as compared with no addition of SCFAs in TSB with sucrose. Biofilm formations of NG4.ΔfimA were inhibited by formic, propionic and valeric acids but not by acetic, butyric, and lactic acids. Addition of 60 mM SCFAs prominently promoted significant attachment of A. oris NG4 and NG4.ΔfimA. However, attachment levels of A. oris ΔfimA were lower than that of A. oris wild type in all conditions.
Conclusions: These suggest that SCFAs have multiple effects on biofilm formations and significant effect on initial attachment in A. oris. Shaft fimbrillin FimA is an important molecule for attachment but not response to stimulation by SCFAs.