Infinite serovar and ribotype heterogeneity among oral Fusobacterium nucleatum strains?

Fusobacterium nucleatum is part of the residential human microbiota and is associated with various infections. It is characterised by broad genetic heterogeneity, but reliable phenotypic markers are lacking. The purpose of the present study was to generate antibodies for the detection of F. nucleatum, to characterise expression patterns of the detected surface antigens on oral isolates, to investigate the prevalence of distinguishable subtypes in clinical samples from the oral cavity, and to compare antigenic with ribotype heterogeneity. Thirty-seven monoclonal antibodies (mAbs) were generated and characterised using strains from 52 taxa. Antibody-binding bacteria were monitored in 35 samples of supra- and subgingival plaque from healthy sites and sites affected by gingivitis or periodontitis. Results indicated broad but structured antigenic heterogeneity. Detecting at least 28 different epitopes, the mAbs defined 19 serovars. Epitopes were expressed on periodate-sensitive polysaccharide chains. Ribotyping of 40 oral F. nucleatum strains (PvuII digestion) resulted in the detection of similarly broad genetic heterogeneity, which rarely corresponded to the observed phenotypic diversity. Clinical samples were generally positive for multiple (up to eight) serovars of which some colonised supra- and subgingival plaques from both healthy and diseased sites, whereas others were restricted to inflamed sites. The majority of the studied isolates could not be grouped with reference strains of the five established subspecies of F. nucleatum, corroborating doubts about the usefulness of the current classification scheme. Although, as a whole the described monoclonal antibodies can only recognise a part of the overwhelming heterogeneity of this 'species', they should prove of value to investigations of the importance, the antigenic stability and the origin of positive subtypes of F, nucleatum from human infections. (C) 1999 Academic Press.