Abstract
Objective and MethodsThe Gram-negative bacterium, Aggregatibacter actinomycetemcomitans is associated with periodontitis affecting young individuals. The geographic dissemination of the highly leukotoxic JP2 genotype of serotype b of this species was previously studied by multilocus sequence typing (MLST). Here, we have used MLST to genetically characterize non-JP2 genotype strains of serotype b, isolated from individuals living in Ghana (n=41), and in Sweden (n=13), respectively.ResultsThe MLST analysis revealed a total of nine sequence types (ST). Both Ghanaian and Swedish isolates were distributed in ST 1-3. ST 5 and 6 were only identified among the Ghanaian strains, whereas ST 4, 7, 8 and 9 were uniquely represented among the Swedish strains. Previously, we characterized these non-JP2 genotype strains of A. actinomycetemcomitans serotype b by arbitrarily-primed (AP)-PCR, which distributed them into three groups, AP-PCR type 1, 2, and 3, respectively. AP-PCR type 1 strains are generally highly leukotoxic, and are associated with progression of periodontal attachment loss. As AP-PCR type 1 includes both JP2 genotype strains and a proportion of non-JP2 genotype strains of serotype b, a straightforward diagnostic procedure has been sought. This has revealed a gene, cagE, which appears to be conserved only in this AP-PCR type. According to our results, MLST was not a highly discriminatory method to identify AP-PCR type 1, as strains of this AP-PCR type could be found within three different ST: ST 2, ST 3 and ST 8.ConclusionAccording to MLST, a geographic dissemination of non-JP2 genotype A. actinomycetemcomitans serotype b appears to exist. However, aiming to identify carriers of AP-PCR type 1, non-JP2 genotype serotype b, PCR with cagE-specific primers is likely the most efficient diagnostic procedure known today.
Highlights
Aggregatibacter actinomycetemcomitans produces a toxin, which associates this bacterium with periodontitis affecting young individuals (Haubek et al, 2008; Henderson et al, 2010; Könönen and Muller, 2014; Fine et al, 2020)
In all of the 56 non-JP2 genotype strains, a total of 290 single nucleotide polymorphisms (SNPs) were detected at the ten polymorphic sites, representing ≈0.1% of the total number of nucleotides of the sequenced gene fragments
We have used Multilocus Sequence Typing (MLST) to investigate the genetic diversity of 56 non-JP2 genotype strains of A. actinomycetemcomitans serotype b, with 41 strains originating from Ghana and 13 from Sweden
Summary
Aggregatibacter actinomycetemcomitans produces a toxin, which associates this bacterium with periodontitis affecting young individuals (Haubek et al, 2008; Henderson et al, 2010; Könönen and Muller, 2014; Fine et al, 2020). Since the toxin causes lethal effects on leukocytes of different types, it is considered a leukotoxin (LtxA). Of the seven serotypes of A. actinomycetemcomitans (a-g), a specific variant of serotype b has a deletion of 530 base pairs (bp) in the promoter region (Brogan et al, 1994). This variant is genetically different from those having a full-length promoter, and is since long referred to as the JP2 genotype (Haubek, 2010). All variants of A. actinomycetemcomitans with a full-length leukotoxin gene promoter are typically referred to as non-JP2 genotype. Additional ltxCABD promoter types have been identified, with either deletions of alternative regions of the promoter, or with insertions in it (He et al, 1999; Claesson et al, 2015; Claesson et al, 2020)
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