Phylogenetic variation of Aggregatibacter actinomycetemcomitans serotype e reveals an aberrant distinct evolutionary stable lineage.

The periodontal pathogen Aggregatibacter actinomycetemcomitans that comprises six serotypes (a-f), is often identified by PCR-based techniques targeting the 16S rRNA gene. In this study, 16S rRNA gene sequence analysis revealed an aberrant cluster of 19 strains within serotype e, denoted as serotype e'. The 16S rRNA gene sequence similarities found between serotype e' strains ranged from 99.7% to 100.0%, whereas 96.8-97.5% sequence similarity was obtained with members of the other serotypes, indicating that the serotype e' strains might not be true members of A. actinomycetemcomitans. However, DNA-DNA hybridizations between a representative serotype e' strain and representative strains of serotypes b, d and e of A. actinomycetemcomitans revealed 68-75% DNA-DNA relatedness, demonstrating that the serotype e' strains do belong to the species A. actinomycetemcomitans. AFLP analysis of 33 A. actinomycetemcomitans strains, representing all serotypes (a-f), but mainly serotype e' strains, showed that the latter form a distinct cluster, demonstrating that these strains are also closely related on the whole genome level. Moreover, the serotype e' strains were unable to ferment starch and glycogen in contrast to almost all other A. actinomycetemcomitans strains tested. Overall, the data obtained in this study suggest that the serotype e' strains form an evolutionary relatively stable distinct subgroup within A. actinomycetemcomitans.

Java project on periodontal diseases: serotype distribution of Aggregatibacter actinomycetemcomitans and serotype dynamics over an 8-year period.

OBJECTIVE: To investigate the serotype distribution and stability of Aggregatibacter actinomycetemcomitans over an 8-year period in untreated Indonesian subjects. MATERIAL AND METHODS: Clinical periodontal status and the presence of A. actinomycetemcomitans were established in 1994 and 2002 in 107 subjects from an Indonesian tea estate deprived from dental care. On an average, 3.6 isolates per patient were subcultured and serotyped using specific PCR reactions. RESULTS: In 1994, the predominant serotype was b (53.7%), whereas a and c occurred in 17.1% and 14.6% of the subjects, respectively. In 2002, a reduction in serotypes a (7.5%) and b (30.2%) occurred. Serotypes c and e increased in prevalence from 14.6% to 35.8% and 2.4% to 9.4%, respectively. Multiple serotypes were found in 12.2% in 1994 and 17% in 2002. From 24 subjects who were positive at both time points, 14 (58.3%) had the same serotype, whereas in 10 subjects (41.7%), a different serotype was found. Mean clinical attachment loss had increased from 0.74 mm in 1994 to 1.96 mm in 2002 but could not be related to subgingival presence of A. actinomycetemcomitans. CONCLUSIONS: A. actinomycetemcomitans serotypes distribution in Indonesian young adults shifts from predominantly serotype b to a more equal prevalence of serotypes b and c. This shift suggests an opportunistic character of A. actinomycetemcomitans.