Effects of the Prevotella intermedia culture filtrate and short-chain fatty acids on human polymorphonuclear neutrophil functions

Anaerobes, in particular Prevotella spp., are the predominant bacteria present in mixed respiratory infections. To study the virulence factor of Prevotella intermedia, we examined the effects of the culture filtrate of P. intermedia on the bactericidal activity of human polymorphonuclear neutrophils (PMNs). The culture filtrate significantly inhibited the phagocytic killing and the intracellular killing of Staphylococcus aureus by PMNs (p < 0.05), but the phagocytosis of PMNs was not affected. The boiled culture filtrate also inhibited the phagocytic killing of PMNs (p < 0.05), which suggests that the inhibitory effect may be mediated by heat-stable substances. Succinic and isovaleric acid were mainly detected from the culture filtrate by gas chromatography. The migration of PMNs was significantly inhibited by these short-chain fatty acids (15 mM succinic acid, p < 0.01 and 1 mM isovaleric acid, p < 0.05). The phagocytic killing of PMNs was significantly inhibited by succinic acid (30 mM, p < 0.05) and not by isovaleric acid. Therefore, these inhibitory effects on human PMN functions may be contributed to the virulence of the mixed infections with anaerobes.