The contribution of htrB gene in Aggregatibacter actinomycetemcomitans virulence

Introduction: The htrB gene has been known to play an important role in the biosynthesis of the LPS polymer. However, studies on its role in virulence of some Gram negative bacteria, including Aggregatibacter actinomycetemcomitans, are contradictory. Objectives: This study was carried out to determine whether the htrB gene has contributions in adhesion/ invasion ability and serum killing of A. actinomycetemcomitans. Methods: To address these questions, a mutant were created using A. actinomycetemcomitans human clinical isolate that were defective in the biosynthesis of acylransferase of lipid A by using homologous recombinant techniques. Subsequently, the effect of mutation was determined in relation to A. actinomycetemcomitans - relationships by performing adhesion-invasion experiments and serum killing assay, using HaCat cell line and fetal bovine serum respectively. Results: The mutant in which htrB is deleted can adhere to and penetrate HaCat cell line, but the numbers were significantly lower than its parent strain. Additionally, inactivation of htrB gene resulted in bacteria phenotype become more sensitive. In conclusion: Our findings indicate that inactivation of the htrB gene affects A. actinomycetemcomitans virulence by decreasing invasiveness and increasing serum bactericidal activity.