Type IV secretion genes in cagE-negative Aggregatibacter actinomycetemcomitans serotype b

Sammanfattning: Aggregatibacter actinomycetemcomitans is a Gram-negative bacterium that plays an important role in the development of aggressive periodontitis. The cagE gene, which encodes a putative exotoxin, has been found to be present in highly leukotoxic serotype b strains. Both in the JP2 genotype, in which there is a 530-bp deletion in the leukotoxin operon’s promoter region, and in the non-JP2 genotype, and it was recently shown that the cagE gene could serve as a genetic marker for highly leukotoxic serotype b strains. It was also noticed that the cagE gene and the virB4 gene did not seem to be found in the same strain. The aim of this study was to determine whether the cagE negative strains of A. actinomycetemcomitans serotype B harboured the virB4 gene and vice versa. We hypothesize that the virB4 gene would be present in the serotype b samples that lacked the cagE gene and vice versa. In order to screen the samples for the presence of the virB4 gene conventional polymerase chain reaction (PCR) and quantitative PCR (qPCR) was used.  Indeed, we found that the cagE gene and the virB4 gene seldom co-existed in the same strain of A. actinomycetemcomitans, i.e. it can function as a marker for non-cagE genotype strains. However, it could also be concluded that it was common for a strain to lack both of these genes.