Phylogenetic Analysis of Strains Isolated from Several Oral Infections Identified a Novel RTX Toxin, FtxA.

is a Gram-positive asaccharolytic, obligate anaerobic rod of the phylum Firmicutes, and is considered an emerging pathogen in various oral infections, including periodontitis. We here aimed to perform phylogenetic analysis of a genome-sequenced type strain (ATCC 35896; CCUG 47790), as well as nine clinical oral strains that we have independently isolated and sequenced, for identification and deeper characterization of novel genomic elements of virulence in this species. We identified that 60% of the strains carried a gene encoding a hitherto unrecognized member of the large repeats-in-toxins (RTX) family, which we have designated as FtxA. The clinical infection origin of the -positive isolates largely varied. However, according to MLST, a clear monophylogeny was reveled for all -positive strains, along with a high co-occurrence of lactate dehydrogenase ()-positivity. Cloning and expression of in , and purification of soluble FtxA yielded a protein of the predicted molecular size of approximately 250 kDa. Additional functional and proteomics analyses using both the recombinant protein and the -positive, and -negative isolates may reveal a possible role and mechanism(s) of FtxA in the virulence properties of , and whether the gene might be a candidate diagnostic marker for more virulent strains.