Porphyromonas gingivalis is a primary pathogen involved in the initiation and 
progression of adult chronic periodontitis. Its colonization on oral surfaces is 
a necessary first step leading to infection. FimA, a subunit protein of major 
(long) fimbriae, is a well-known virulence factor. Based on its nucleotide 
sequence, FimA is classified into several genotypes. We compared here the 
transcriptional levels of the fimA gene in several P. gingivalis strains using 
real-time polymerase chain reaction analysis, fimbrial display on the P. 
gingivalis surface using transmission electronic microscopy, and the adherence 
competencies of P. gingivalis strains carrying different types of FimAs towards 
saliva and Streptococcus gordonii surfaces using mutagenesis analysis. We 
demonstrated differential expression of each fimA gene in these P. gingivalis 
strains. A correlation of the transcription level of fimA and binding activity 
of P. gingivalis was revealed. We show that P. gingivalis strains with genotype 
I and II of FimA are efficient in interaction with saliva or S. gordonii. This 
work highlights the important role of FimA type I and II in P. gingivalis 
attachment to oral surfaces.