| Abstrakt: |
ABSTRACTThe periodontal pathogen Actinobacillus actinomycetemcomitanspossesses myriad virulence factors, among them the ability to adhere to and invade epithelial cells. Recent advances in the molecular manipulation of this pathogen and the sequencing of strain HK 1651 (http://www.genome.ou.edu/act.html) have facilitated examination of the genetics of its interaction with epithelial cells. The related gram-negative organism, Haemophilus influenzae, possesses autotransporter adhesins. A search of the sequence database of strain HK 1651 revealed a homologue with similarity in the pore-forming domain to that of the H. influenzaeautotransporter, Hap. A. actinomycetemcomitansmutants deficient in the homologue, Aae, showed reduced binding to epithelial cells. A method for making A. actinomycetemcomitansSUNY 465 transiently resistant to spectinomycin was used with conjugation to generate an isogenic aaemutant. An allelic replacement mutant was created in the naturally transformable A. actinomycetemcomitansstrain ATCC 29523. Lactoferrin, an important part of the innate host defense system, protects against bacterial infection by bactericidal and antiadhesion mechanisms. Lactoferrin in human milk removes or cleaves Hap and another autotransporter, an immunoglobulin A1 protease, from the surface of H. influenzae, thereby reducing their binding to epithelial cells. Human milk whey had similar effects on Aae from A. actinomycetemcomitansATCC 29523 and its binding to epithelial cells; however, there was little effect on the binding of SUNY 465. A difference in the genetic structure of aaein the two strains, apparently due to the copy number of a 135-base repeated sequence, may be the cause of the differential action of lactoferrin. aaeis the first A. actinomycetemcomitansgene involved in adhesion to epithelial cells to be identified. |
