Virulence of Aggregatibacter actinomycetemcomitans serotypes and DGGE subtypes isolated from chronic adult periodontitis in Thailand.

A high proportion of non-serotypeable isolates of Aggregatibacter actinomycetemcomitans among Thai periodontitis cases has been previously reported. The aim of this study was to investigate the expression of leukotoxin and toxicity, cytolethal distending toxin (Cdts), and internalization and the killing effect on fibroblasts by A. actinomycetemcomitans subtypes from Thai chronic periodontitis cases. A total of 96 A. actinomycetemcomitans strains from 37 periodontitis cases, previously serotyped with PCR and subtyped with DGGE, were examined for the presence of the ltx gene and cdt genes (cdtBC), and tested for leukotoxin expression, leukotoxicity, internalization, and apoptosis of fibroblast cells. The ltx gene was present in all isolates, while 84.4% showed the cdtBC gene. Two strains with a JP2-like ltx gene with a deletion of 530 bp in the promoter region, serotyped as c, showed virulence of similar magnitude to the JP2 strain. Furthermore, a higher virulence was found in the two non-serotypeable DGGE subtypes, NS1 and NS2, compared with the serotypeable strains (serotype a-f, serotype b and d were absent). Generally, the virulence of strains obtained from deep periodontal pockets was higher than those isolated from shallow non-bleeding pockets. A. actinomycetemcomitans subtypes isolated from adult Thais with chronic periodontitis showed a highly variable virulence, leukotoxin expression, leukotoxicity, internalization and apoptosis of fibroblast, and are regulated both genetically and environmentally.