Genetic and antigenic analyses of <scp><i>Porphyromonas gingivalis</i></scp> FimA fimbriae

<jats:title>Summary</jats:title><jats:p>The periodontal pathogen <jats:styled-content style="fixed-case"><jats:italic>Porphyromonas gingivalis</jats:italic></jats:styled-content> generally expresses two distinct fimbriae, FimA and Mfa1, which play a role in biofilm formation. The <jats:italic>fimA</jats:italic> gene that encodes FimA fimbrilin is polymorphic, and polymerase chain reaction analysis has identified six genotypes called types I–V and Ib. We found recently that fimbriae exhibit antigenic heterogeneity among the genotypes. In the present study, we analysed the <jats:italic>fimA </jats:italic><jats:styled-content style="fixed-case">DNA</jats:styled-content> sequences of 84 strains of <jats:italic>P. gingivalis</jats:italic> and characterized the antigenicity of FimA fimbriae. Strains analysed here comprised 10, 16, 29, 13, 10 and 6 strains of types I, Ib, <jats:styled-content style="fixed-case">II</jats:styled-content>,<jats:styled-content style="fixed-case"> III</jats:styled-content>,<jats:styled-content style="fixed-case"> IV</jats:styled-content> and V, respectively. <jats:styled-content style="fixed-case">DNA</jats:styled-content> sequencing revealed that type Ib does not represent a single cluster and that type <jats:styled-content style="fixed-case">II</jats:styled-content> sequences are remarkably diverse. In contrast, the <jats:italic>fimA</jats:italic> sequences of the other types were relatively homogeneous. Antigenicity was investigated using antisera elicited by pure FimA fimbriae of types I–V. Antigenicity correlated generally with the respective genotype. Type Ib strains were recognized by type I antisera. However, some strains showed cross‐reactivity, especially, many type <jats:styled-content style="fixed-case">II</jats:styled-content> strains reacted with type <jats:styled-content style="fixed-case">III</jats:styled-content> antisera. The levels of fimbrial expression were highly variable, and expression was positively correlated with ability of biofilm formation on a saliva‐coated plate. Further, two strains without FimA and Mfa1 fimbriae expressed fimbrial structures, suggesting that the strains produce other types of fimbriae.</jats:p>