Actinomyces naeslundii genospecies 1 and 2 express different binding specificities to N-acetyl-beta-D-galactosamine, whereas Actinomyces odontolyticus expresses a different binding specificity in colonizing the human mouth.

A total of 102 strains of Actinomyces were isolated from teeth, buccal mucosa and tongue in eight individuals. The isolates were characterized by multivariate statistical analyses of phenotypic characteristics, serotyping and binding to beta-linked galactosamine (N-acetyl-beta-D-galactosamine) and acidic proline-rich protein structures. Based on these characteristics, isolates were classified into three major groups: (i) Isolates of Actinomyces naeslundii genospecies 2 were the dominant species on teeth and buccal mucosa and bound commonly to N-acetyl-beta-D-galactosamine (63 of 63 isolates) and acidic proline-rich proteins (63 of 63 isolates), regardless of tissue origin. They all exhibited a N-acetyl-beta-D-galactosamine binding specificity signified by N-acetyl-beta-D-galactosamine-inhibitable coaggregation with the streptococcal strains LVG1, GVE1, 24892 and MPB1; (ii) Isolates of A. naeslundii genospecies 1 were prevalent on teeth in certain individuals and bound commonly to N-acetyl-beta-D-galactosamine (20 of 20 isolates), but less commonly to acidic proline-rich proteins (5 of 20 isolates). They all possessed another N-acetyl-beta-D-galactosamine specificity, i.e. N-acetyl-beta-D-galactosamine-inhibitable coaggregation with the same streptococcal strains except for strain MPB1; (iii) Isolates of Actinomyces odontolyticus, the dominant species on the tongue (17 of 19 isolates), bound commonly to unknown structures on streptococci (17 of 19 isolates) but rarely to N-acetyl-beta-D-galactosamine (2 of 19 isolates) or acidic proline-rich proteins (3 of 19 isolates). In conclusion, A. naeslundii genospecies 1 and 2 exhibit different patterns of N-acetyl-beta-D-galactosamine and acidic proline-rich protein specificities to colonize dental and buccal mucosa surfaces, whereas A. odontolyticus utilizes another specificity to colonize the tongue.