Autoinducer-2 and QseC Control Biofilm Formation and In Vivo Virulence of Aggregatibacter actinomycetemcomitans

Abstract

Biofilm formation by the periodontal pathogen Aggregatibacter actinomycetemcomitans is dependent upon autoinducer-2 (AI-2)-mediated quorum sensing. However, the components that link the detection of the AI-2 signal to downstream gene expression have not been determined. One potential regulator is the QseBC two-component system, which is part of the AI-2-dependent response pathway that controls biofilm formation in Escherichia coli. Here we show that the expression of QseBC in A. actinomycetemcomitans is induced by AI-2 and that induction requires the AI-2 receptors, LsrB and/or RbsB. Additionally, inactivation of qseC resulted in reduced biofilm growth. Since the ability to grow in biofilms is essential for A. actinomycetemcomitans virulence, strains that were deficient in QseC or the AI-2 receptors were examined in an in vivo mouse model of periodontitis. The ⌬qseC mutant induced significantly less alveolar bone resorption than the wild-type strain (P < 0.02). Bone loss in animals infected with the ⌬qseC strain was similar to that in sham-infected animals. The ⌬lsrB, ⌬rbsB, and ⌬lsrB ⌬rbsB strains also induced significantly less alveolar bone resorption than the wild type (P < 0.03, P < 0.02, and P < 0.01, respectively). However, bone loss induced by a ⌬luxS strain was indistinguishable from that induced by the wild type, suggesting that AI-2 produced by indigenous microflora in the murine oral cavity may complement the ⌬luxS mutation. Together, these results suggest that the QseBC two-component system is part of the AI-2 regulon and may link the detection of AI-2 to the regulation of downstream cellular processes that are involved in biofilm formation and virulence of A. actinomycetemcomitans.

Carrageenin-Induced Periodontitis as an Experimental Model in Rats Analyzed by Micro-Computerized Tomography

“…Porphyrononas gingivalis 6,7,[11][12][13] , Fusobacterium nucleatum 7,13) and Aggregatibacter actinomycetemcomitans 8) . Using our novel method, experimental periodontitis developed in all rats; in other words, this carrageenin method caused experimental periodontitis with severe bone loss in 100% of rats.…”

“…On the other hand, although rodents including rats and mice are resistant to periodontitis naturally, they are used for periodontal research [3][4][5][6] , since they are easy to handle and are inexpensive 10) . In rats and mice, experimental periodontitis is induced by inoculation of bacteria [6][7][8][11][12][13] and placement of ligatures 5,[14][15][16][17] ; however, for inoculation of bacteria, the experiment includes bacteria culture, the method of inoculating bacteria is complicated, and a long period is required to establish periodontitis. Although the experimental method of ligature placement is a simple model, the upper jaw was selected as the experimental target in previous studies 5, [14][15][16] , since the cheek and tongue act as obstacles in lower jaw operations; however, since periodontitis occurs not only in the maxilla but also the mandibule, a simple, easy and reliable experimental model of mandibule in rats and/or mice is required for research for periodontitis.…”

“…Many kinds of animals have been used for periodontitis research previously, non-human primates 1,2) , dogs 3,4) , rats 5,6) , mice 7,8) and so on 9) ; however, each of these animals has particular characteristics. For example, in non-human primates and dogs, the progress of periodontitis is similar to that in humans; however, they are difficult to handle and are expensive 10) .…”

Transcriptional regulation of the Aggregatibacter actinomycetemcomitans ygiW–qseBC operon by QseB and integration host factor proteins

“…A. actinomycetemcomitans is a non-motile organism and lacks many of the genes that are regulated by QseBC in E. coli and Salmonella. Yet A. actinomycetemcomitans QseBC clearly plays a role in virulence, since deletion of qseC dramatically reduces biofilm growth and leads to a virulence attenuated phenotype (Novak et al, 2010;Juárez-Rodríguez et al, 2013a). This suggests that the function of QseBC in A. actinomycetemcomitans may differ from that in E. coli and other enteric organisms.…”

“…A. actinomycetemcomitans biofilm formation, iron acquisition and virulence are also regulated by a quorum-sensing system that responds to autoinducer AI-2 (Demuth et al, 2011;Fong et al, 2001Fong et al, , 2003. The QseBC two-component system is part of this quorum-sensing system and is regulated by AI-2 (Novak et al, 2010). In A. actinomycetemcomitans, the qseBC genes are co-expressed with ygiW, which codes for a polypeptide of unknown function in the OB-fold family of proteins and the operon is transcribed from a promoter that resides upstream of ygiW (Juárez-Rodríguez et al, 2013a).…”