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Aggregatibacter actinomycetemcomitans: A Unique Exotoxin-Producing Oral Bacterium

The production and secretion of protein toxins (exotoxins) is a most common strategy among microbial pathogens. Yet, oddly, these virulence factors are fairly rare among oral pathogens, with one exception, the Gram-negative Aggregatibacter actinomycetemcomitans. For readers with an interest in taxonomy, this microbe was originally named Actinobacillus actinomycetemcomitans and later reclassified and renamed (you known taxonomists...). The new genus name refers to the microbe’s tendency to aggregate with other bacteria in the dental plaque, whereas the equally bombastic species name speaks to the fact that it was isolated together with the common mouth-dwelling Actinomyces. This microbe makes pretty colonies that look like a flower. But, esthetics aside, this microbe has attributes that warrant special attention. It is found in about one third of the human population and it is involved in a particularly rapid progressive form of adolescent periodontal disease, common in those of African descent. It has also been implicated in infective endocarditis and other deep serious infections. Viable cells of A. actinomycetemcomitans cellshave been identified in atherosclerotic plaque. This is, without a doubt, a microbe that knows how to cause trouble. But what makes it so prominent in the oral environment and such a successful pathogen?

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