Chemical and functional characterization of exopolysaccharide from a clinical isolate of Prevotella nigrescens

Abstract

Prevotella nigrescens, a Gram-negative black-pigmented anaerobic rod, is frequently isolated from periodontitis and periapical lesions. We isolated an exopolysaccharide (EPS)-producing P. nigrescens, strain 22, from a chronic periodontitis lesion. In this study, we characterized the chemical structure of the purified EPS from strain 22, and studied the biological effects of EPS on abscess formation in mice and on the phagocytosis of peripheral blood polymorphonuclear leukocytes using strain 22, heat-killed strain 22, and an EPS-non-producing mutant, strain 328. EPS exhibited anti-phagocytic activity in vitro, and strain 22 and its heat-killed counterpart induced large abscesses in mice. However, strain 328 did not induce abscesses. These results suggest that one of the functions of EPS produced by strain 22 is to protect the bacteria from the phagocytotic system in order to ensure a longer survival of the organism in the host.