Comparison of the Pathogenicity of Isolates of Hyperinvasive Sequence Type 7 Belonging to Serogroups A, B, C, and X.

Objective: To compare the pathogenicity of isolates of sequence type 7 (ST-7) ( ) belonging to four different serogroups (A, B, C, and X).

Methods: Four ST-7 isolates serogrouped as A, B, C, and X and characterized by different capsule structures, were examined for their adhesion and invasion properties, and their ability to induce cytokine release and apoptosis in the host cell (the A549 cell line).

Results: Among the four ST-7 isolates, the serogroup A isolate possessed the strongest adhesion and invasion ability. This isolate also induced the release of the highest levels of the pro-inflammatory mediators interleukin-6, interleukin-1β, and interferon, and the highest apoptosis rate in the host cells. However, there was no significant difference in interleukin-8 and tumor necrosis factor-α secretion between the four isolates. Based on the findings, the serogroup X isolate had the weakest pathogenicity, whereas there was almost no difference in the pathogenicity of the isolates from serogroups B and C.

Conclusions: The differences in the capsular structure of the four isolates of ST-7 affected their pathogenic capacities. The findings also imply that the hyperinvasive ST-7 lineage may include hypoinvasive isolates.