<i>Aggregatibacter actinomycetemcomitans</i> Leukotoxin

Kachlany, Scott C.

doi:10.1177/0022034510363682

Cited by 127 publications

(126 citation statements)

References 114 publications

(156 reference statements)

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“…4). The remaining 2 genes, however, encoded less well recognized biofilm determinants-leukotoxin (ltxB [19]) and the DNA uptake transcriptional regulator TfoX (71). Leukotoxin is widely regarded as the primary virulence factor of A. actinomycetemcomitans, as it lyses both white and red blood cells (20), but recently it was also shown to control adherence.…”

Section: Discussionmentioning

confidence: 99%

Defining Genetic Fitness Determinants and Creating Genomic Resources for an Oral Pathogen

Narayanan

Ramsey

Stacy

et al. 2017

Appl Environ Microbiol

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Periodontitis is a microbial infection that destroys the structures that support the teeth. Although it is typically a chronic condition, rapidly progressing, aggressive forms are associated with the oral pathogen Aggregatibacter actinomycetemcomitans. One of this bacterium's key virulence traits is its ability to attach to surfaces and form robust biofilms that resist killing by the host and antibiotics. Though much has been learned about A. actinomycetemcomitans since its initial discovery, we lack insight into a fundamental aspect of its basic biology, as we do not know the full set of genes that it requires for viability (the essential genome). Furthermore, research on A. actinomycetemcomitans is hampered by the field's lack of a mutant collection. To address these gaps, we used rapid transposon mutant sequencing (Tn-seq) to define the essential genomes of two strains of A. actinomycetemcomitans, revealing a core set of 319 genes. We then generated an arrayed mutant library comprising Ͼ1,500 unique insertions and used a sequencing-based approach to define each mutant's position (well and plate) in the library. To demonstrate its utility, we screened the library for mutants with weakened resistance to subinhibitory erythromycin, revealing the multidrug efflux pump AcrAB as a critical resistance factor. During the screen, we discovered that erythromycin induces A. actinomycetemcomitans to form biofilms. We therefore devised a novel Tnseq-based screen to identify specific factors that mediate this phenotype and in follow-up experiments confirmed 4 mutants. Together, these studies present new insights and resources for investigating the basic biology and disease mechanisms of a human pathogen. IMPORTANCE Millions suffer from gum disease, which often is caused by Aggregatibacter actinomycetemcomitans, a bacterium that forms antibiotic-resistant biofilms. To fully understand any organism, we should be able to answer: what genes does it require for life? Here, we address this question for A. actinomycetemcomitans by determining the genes in its genome that cannot be mutated. As for the genes that can be mutated, we archived these mutants into a library, which we used to find genes that contribute to antibiotic resistance, leading us to discover that antibiotics cause A. actinomycetemcomitans to form biofilms. We then devised an approach to find genes that mediate this process and confirmed 4 genes. These results illuminate new fundamental traits of a human pathogen.KEYWORDS Aggregatibacter, Tn-seq, antibiotics, biofilms, essential genome O ne of the longest-studied human microbiomes is the "animalcules" (bacteria), first observed by van Leeuwenhoek (1), that inhabit the oral cavity. Oral bacteria readily attach to tooth surfaces and develop into spatially organized, multispecies biofilms (2). These communities also persist beneath the gum line in the subgingival pocket, where they are kept in check by host immune cells (3). Though normally benign, subgingival communities can accumulate opportunistic oral p...

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Section: Discussionmentioning

confidence: 99%

Defining Genetic Fitness Determinants and Creating Genomic Resources for an Oral Pathogen

Narayanan

Ramsey

Stacy

et al. 2017

Appl Environ Microbiol

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“…The Cdt causes growth arrest and eventually apoptosis to virtually all eukaryotic cells [10][11][12][13]. Leukotoxin, predominantly associated with the bacterial surface [14,15], can selectively kill human leukocytes by triggering apoptosis or lysis [16][17][18][19]. The lysis of human monocytes / macrophages by leukotoxin is mediated by the activation of the cysteine proteinase Caspase-1, which is also associated with the secretion of bio-active IL-1β [17,20,21].…”

Section: Introductionmentioning

confidence: 99%

Aggregatibacter actinomycetemcomitans targets NLRP3 and NLRP6 inflammasome expression in human mononuclear leukocytes

Belibasakis

Johansson

2012

Cytokine

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Periodontitis is an inflammatory condition that destroys the tooth-supporting tissues, as a result of local bacterial infection. Aggregatibacter actinomycetemcomitans is a Gram-negative facultative anaerobic species, highly associated with aggressive periodontitis. Periodontal inflammation is dominated by cytokines of the Interleukin (IL)-1 family. Prior to their secretion by mononuclear cells, IL-1 cytokines are processed by intracellular protein complexes, known as "inflammasomes", which can sense the bacterial challenge. The aim of this study was to investigate which inflammasomes are regulated in mononuclear cells in response to A. actinomycetemcomitans. The D7SS strain and its derivative leukotoxin and cytolethal distending toxin knock-out mutant strains were used to infect human mononuclear cells at a 1:10 cell: bacteria ratio, for 3 h. The expression of various inflammasome components in the cells was investigated by TaqMan quantitative real-time polymerase chain reaction (qPCR). The expressions of NOD-like receptor protein (NLRP)1, NLRP2 and Absent In Melanoma (AIM)2 inflammasome sensors, as well as their effector Caspase-1 were not affected. However, NLRP3 was up-regulated, while NLRP6 was down-regulated. This effect was not dependent on the leukotoxin or the cytolethal distending toxin, as demonstrated by the use of specific gene knock-out mutant strains. IL-1 and IL-18 expressions were also up-regulated by the bacterial challenge. In conclusion, A. actinomycetemcomitans enhances NLRP3 and reduces NLRP6 inflammasome expression, irrespective of its major virulence factors, confirming the high pathogenic profile of this species, and providing further insights to the mechanisms of periodontal inflammation. actinomycetemcomitans enhances NLRP3 and reduces NLRP6 inflammasome expression, irrespective of its major virulence factors, confirming the high pathogenic profile of this species, and providing further insights to the mechanisms of periodontal inflammation.

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“…The high accumulation of this clone in subjects of African origin has indicated a possible host tropism, but could also be a result of the strict vertical transmission pattern of this bacterium Haubek 2010). The expression of leukotoxin is also regulated by environmental factors, such as growth conditions and substrates (Kachlany et al, 2010). The expression of leukotoxin by various strains of A. actinomycetemcomitans at the infected site of the host is still unknown.…”

Section: Expression and Secretion Of A Actinomycetemcomitans Leukotoxinmentioning

confidence: 99%

“…The cellular and molecular mechanisms for the hemolytic effect of leukotoxin are unknown. The lysis of erythrocytes by the leukotoxin has recently been reviewed (Kachlany 2010). It remains to be answered whether the hemolytic capacity of leukotoxin is an important virulence factor in periodontitis.…”

Section: Erythrocytesmentioning

confidence: 99%