ACTINOMYCES-NAESLUNDII DISPLAYS VARIANT FIMP AND FIMA FIMBRIAL SUBUNIT GENES CORRESPONDING TO DIFFERENT TYPES OF ACIDIC PROLINE-RICH PROTEIN AND BETA-LINKED GALACTOSAMINE BINDING-SPECIFICITY

Actinomyces naeslundii genospecies 1 and 2 bind to acidic proline-rich proteins (APRPs) and statherin via type 1 fimbriae and to P-linked ga lactosamine (GalNAc beta) structures via type 2 fimbriae. In addition, A. naeslundii displays two types of binding specificity for both APRP s-statherin and GalNAc beta, while Actinomyces odontolyticus binds to unknown structures. To study the molecular basis for these binding spe cificities, DNA fragments spanning the entire or central portions of f imP (type 1) and fimA (type 2) fimbrial subunit genes were amplified b y PCR from strains of genospecies 1 and 2 and hybridized with DNA from two independent collections of oral Actinomyces isolates. Isolates of genospecies 1 and 2 and A. odontolyticus, but no other Actinomyces sp ecies, were positive for hybridization with fimP and fimA full-length probes irrespective of binding to APRPs and statherin, GalNAc beta, or unknown structures. Isolates of genospecies 1 and 2, with deviating p atterns of GalNAc beta 1-3Gal alpha-O-ethyl-inhibitable coaggregation with Streptococcus oralis Ss34 and MPB1, were distinguished by a fimA central probe from genospecies 1 and 2, respectively. Furthermore, iso lates of genospecies 1 and 2 displaying preferential binding to APRPs over statherin were positive with a fimP central probe, while a genosp ecies 2 strain with the opposite binding preference was not. The seque nces of fimP and fimA central gene segments were highly conserved amon g isolates with the same, but diversified between those with a variant , binding specificity. In conclusion, A. naeslundii exhibits variant f imP and fimA genes corresponding to diverse APRP and GalNAc beta speci ficities? respectively, while A. odontolyticus has a genetically relat ed but distinct adhesin binding specificity.