Comparative Analysis on the Halo-forming Colony Strain and its Variant of Aggregatibacter actinomycetemcomitans

Abstract

Halo-forming colony and its variant (non-halo forming) strains, designated NUM-Aa 5014 and NUM-Aa 5016, respectively, were isolated from periodontitis. They were identified as Aggregatibacter actinomycetemcomitans serotype f. The NUM-Aa 5014 strain showed an aggregated form in the broth culture and strong biofilm formation on hard surfaces, while NUM-Aa 5016 did not show this phenomenon. In a Congo red (CR)-binding assay, the halo-forming colony strain NUM-Aa 5014 was strongly bound by CR. ATCC 33384T and NUM-Aa 5016 showed low binding activity. The tight adherence (tad) locus of the NUM-Aa 5014 and 5016 strains contained 14 genes, flp-1-flp-2-tadV-rcpCAB-tadZABCDEFG, in 11,565 and 11,574 bp, respectively. Almost all genes were the same except the flp-1 and tadD genes between the NUM-Aa 5014 and 5016 strains. The homologies of flp-1 and tadD genes in the NUM-Aa 5014 and 5016 strains were 97.4% and 99.6% in amino acid sequences, respectively. These results suggest that the expression of genes in tad locus may play some roles in adherence and aggregation of A. actinomycetemcomitans.