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Updated: May 10, 2026
Porphyromonas gingivalis as a Model Organism for Assessing Interaction of Anaerobic Bacteria with Host Cells
Published on: December 17, 2015
Genetic and antigenic analyses of Porphyromonas gingivalis FimA fimbriae
1Department of Microbiology, School of Dentistry, Aichi Gakuin University, Nagoya, Japan. nagano@dpc.agu.ac.jp
Abstract:
The periodontal pathogen Porphyromonas gingivalis generally expresses two distinct fimbriae, FimA and Mfa1, which play a role in biofilm formation. The fimA 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 fimA DNA sequences of 84 strains of P. gingivalis and characterized the antigenicity of FimA fimbriae. Strains analysed here comprised 10, 16, 29, 13, 10 and 6 strains of types I, Ib, II, III, IV and V, respectively. DNA sequencing revealed that type Ib does not represent a single cluster and that type II sequences are remarkably diverse. In contrast, the fimA 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 II strains reacted with type III 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.
Insights
Porphyromonas gingivalis fimbriae (FimA) show genetic and antigenic diversity across genotypes. FimA expression levels correlate with biofilm formation, and some strains may produce other fimbriae.
Area of Science:
- Microbiology
- Oral Health
- Bacterial Pathogenesis
Background:
- Porphyromonas gingivalis is a key periodontal pathogen.
- Fimbriae (FimA and Mfa1) are crucial for biofilm formation.
- The fimA gene exhibits genetic polymorphism, with six identified genotypes (types I-V and Ib).
Purpose of the Study:
- To analyze fimA DNA sequences of 84 P. gingivalis strains.
- To characterize the antigenicity of FimA fimbriae across different genotypes.
- To investigate the correlation between fimbrial expression, antigenicity, and biofilm formation.
Main Methods:
- DNA sequencing of the fimA gene from 84 P. gingivalis strains.
- Antigenicity testing using antisera against purified FimA fimbriae (types I-V).
- Quantification of fimbrial expression and assessment of biofilm formation on saliva-coated plates.
Main Results:
- Type Ib fimA sequences were not a single cluster; type II sequences showed high diversity.
- FimA antigenicity generally correlated with genotype, with cross-reactivity observed (e.g., type Ib with type I, type II with type III).
- Fimbrial expression levels varied significantly and positively correlated with biofilm formation ability.
Conclusions:
- P. gingivalis FimA fimbriae display significant genetic and antigenic heterogeneity.
- Antigenic variation may impact immune recognition and host-pathogen interactions.
- Fimbrial expression is a key factor in P. gingivalis biofilm formation, a critical aspect of periodontitis pathogenesis.
- Some P. gingivalis strains may express alternative fimbrial structures beyond FimA and Mfa1.
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