A Comparison of Aggregatibacter actinomycetemcomitans (Aa) Virulence Traits in a Rat Model for Periodontal Disease

Abstract

Our aim was to explore the effects of Cytolethal Distending toxin (Cdt) in a well established rat model of periodontal disease where leukotoxin (LtxA) was thought to have no known effect. In vitro studies, were used to assess CdtB activity using Aa Leukotoxin as a negative control. These studies showed that both CdtB and LtxA (unexpectedly) exerted significant effects on CD4+ T cells. As a result we decided to compare the effects of these two prominent Aa virulence factors on bone loss using our rat model of Aa-induced periodontitis. In this model, Aa strains, mutant in cdtB and ltxA, were compared to their parent non-mutant strains and evaluated for colonization, antibody response to Aa, bone loss and disease. We found that bone loss/disease caused by the ltxA mutant strain, in which cdtB was expressed, was significantly less (p<0.05) than that due to the wild type strain. On the other hand, the disease caused by cdtB mutant strain, in which ltxA was expressed, was not significantly different from the wild type strain. This data indicates that Aa LtxA exerts a greater effect on bone loss than Cdt in this rat model of periodontal disease and supports the utility of this model to dissect specific virulence factors as they relate to immunopathology in studies of Aa-induced disease.

Colonization and Persistence of Labeled and “Foreign” Strains of Aggregatibacter actinomycetemcomitans Inoculated into the Mouths of Rhesus Monkeys

“…We performed an overall genome sequence analysis of “a”, “b”, “c” and “d” serotypes from A. actinomycetemcomitans strains isolated from Rh monkeys from the NEPRC primate center [27]. We also chose IDH 781, a human “d” serotype A. actinomycetemcomitans strain for our comparison in the inoculation studies because of its success in our in vitro binding assays and in our in vivo rat studies [9]. …”

“…We collected several dozen A. actinomycetemcomitans strains with a range of serotypes from the Rh primates at the NEPRC (Table 1). We compared the attachment characteristics of several of these primate strains to human A. actinomycetemcomitans strain IDH 781, considered an outstanding colonizing bacterium in vitro and in our rat studies [9,13]. Initially we compared binding of various A. actinomycetemcomitans primate and human strains to buccal epithelial cells (BECs) and salivary-coated hydroxyapatite (SHA).…”

“…Towards these ends our group has developed both in vitro assays and in vivo animal models to study A. actinomycetemcomitans colonization and survival [7,8]. Most recently, we demonstrated that A. actinomycetemcomitans leukotoxin, previously thought to be active exclusively in humans and primates, is a prominent virulence factor associated with bone resorption in a rat model of periodontal disease [9]. …”

“…While we have had significant success in studying colonization in our rat model, the in vitro rat lymphocytic response to A. actinmycetemcomitans leukotoxin was modest suggesting that the in vivo rat model under-represented the bone loss detected [9]. Furthermore bone loss is the end stage of disease [10].…”

Bacterial fight-and-flight responses enhance virulence in a polymicrobial infection

“…Aa elaborates an array of virulence factors that enhance its survival and directly harm the host during infection, including leukotoxin (13), cytolethal distending toxin (14), CagE (15), fimbriae (16), and LPS (17). Several of these virulence factors contribute to bone loss, a signature of aggressive periodontitis, in various animal models (17,18). However, despite Aa living in a microbe-rich environment, Aa-host interactions are less frequently investigated in the context of other oral microbes.…”