The Regulation of Leukotoxin Production in Actinobacillus Actinomycetemcomitans Strain JP2

Abstract

Actinobacillus actinomycetemcomitans (A.a.) can produce a potent leukotoxin that is thought to be involved in evasion of the host immune response. In order to understand the role of A.a. and its leukotoxin in the initiation and progression of periodontal disease, it is important determine how the expression of A.a. virulence factors might be regulated by the local periodontal micro-environment. To facilitate the measurement of leukotoxin levels, a leukotoxin-beta-galactosidase gene fusion was constructed and recombined into the chromosome of A.a. strain JP2 at the leukotoxin locus. The resulting strain, AAM17, produces beta-galactosidase under control of the leukotoxin promoter. It also produces leukotoxin, since integration of the gene fusion into the chromosome was designed to produce a duplication of the leukotoxin gene. This strain was used to measure the change in leukotoxin level in response to alterations in two environmental signals: iron concentration and oxygen tension. When AAM17 was grown in iron-limited media that did not alter growth rate but did increase the levels of other iron-regulated proteins, the levels of the leukotoxin-beta-galactosidase were similar to those found in AAM17 grown in iron-replete media. These results were confirmed in strains AAM17 and JP2 by leukotoxicity assays and RNA blots. Aerobic growth of AAM17 resulted in a three-fold decrease in leukotoxin beta-galactosidase activity compared with anaerobically grown cells. These results indicate that the A.a. leukotoxin is regulated by some of the environmental signals that may vary in the gingival crevice.

Potential of Diagnostic Microbiology for Treatment and Prognosis of Dental Caries and Periodontal Diseases

“…For example, leukotoxin expression may vary among strains of A. actinomycetemcomitans; various strains of P. gingivalis may differ in their production of proteolytic enzymes. Some of these differences may be partly due to environmental factors but seem to be also genetically regulated (Kuramitsu et al, 1995;Spitznagel et al, 1995). This might explain why species suspected to be pathogens can be found in healthy sites or subjects.…”

The Role of Acquired Immunity and Periodontal Disease Progression

“…In addition, some periodontal pathogens produce "attacking" arsenals (i.e., proteases) that destroy IgA, IgG, and even B-cells to counteract the host's immune protection (Spitznagel et al, 1995;Gronbaek Frandsen, 1999;Yun et al, 2001). Therefore, orchestrating the bacterial evasion, opsonization, phagocytosis, cell-mediated immune response, and regulation by the cytokine network could successfully lead to Abmediated immune protection during periodontal infection.…”

Leukotoxic Activity of Actinobacillus Actinomycetemcomitans Isolated From Human and Non-Human Primates

“…Hritz et al (8) reported that the production of leukotoxin is repressed by aeration, and this oxygen-dependent regulation differs significantly between highly toxic and minimally toxic A. actinomycetemcomitans strains (JP2 and 652, respectively), resulting in different levels of leukotoxic protein production rather than a change in toxin activity (21). In our study, the M 22.11 and P 2.17 strains were not influenced by aeration, i.e., they behaved similarly to JP2 strain.…”