FimA Genotypes and Multilocus Sequence Types in Porphyromonas gingivalis

Fimbriae are considered important virulence factors of bacterial pathogens facilitating attachment of bacteria to host cells. In the periodontal pathogen Porphyromonas gingivalis, the fimA gene is classified into six types (I, Ib, II, III, IV, and V) based on different nucleotide sequences. The fimA genotype II is most prevalent in severe periodontitis, while the fimA type I is associated with periodontally healthy subjects. Objective: The aims of this study were to examine distribution of fimA genotypes in a collection of 60 P. gingivalis isolates of worldwide origin from periodontitis patients, and to investigate the relationship between fimA genotypes and different sequence types (STs) obtained by using multilocus sequence typing (MLST). Methods: Chromosomal DNA was extracted from 60 P. gingivalis isolates using the CTAB method. FimA genes were amplified by PCR using specific primer sets for each genotype, as described by other investigators. The multilocus genotypes of all strains were assigned according to our MLST database for P. gingivalis (www.pubmlst.org/pgingivalis). Relationship between strains was analyzed by the construction of a UPGMA dendrogram. Results: 40 % of the strains harbored fimA type II, while 18% of the isolates were positive in more than one reaction. Most frequent combinations were I and II or Ib and II. None of the isolates reacted with primers for fimA genotype V. The 60 strains were assigned to 51 STs. Cluster analysis showed extensive diversity of STs. The different fimA genotypes were distributed throughout the dendrogram and only isolates with closely related STs were seen to harbor the same fimA type. Conclusions: Different fimA genotypes were evenly distributed in relation to STs and geographic origin confirming extensive diversity of P. gingivalis. Our results also indicated that single isolates can contain multiple fimA genotypes. Further studies are needed to elucidate the extent of fimA variation in P. gingivalis.