May 1, 2006
Researchers have known for years that the oral bacterium with the torturously long name of Actinobacillus actinomycetemcomitans can cause juvenile periodontal disease. Less well established is the bacterium’s possible role in systemic disease. Part of this uncertainty hinges on a conflicting data on the bacterium’s ability to break open red blood cells, a virulence trait called hemolysis that clinical microbiologists frequently evaluate to identify pathogens in diagnostic laboratories. Some previous studies have indicated that certain strains of A. actinomycetemcomitans are beta hemolytic, meaning they completely lyse red blood cells, while several other studies have found just the opposite. In the April issue of the journal Infection and Immunity, NIDCR grantees report that the answer might fall somewhere in between. The scientist found that the bacterium’s hemolytic ability varied with the choice of growth medium employed in the laboratory. Interestingly, when beta hemolysis was detected, it was conferred by the bacterium’s much studied leukotoxin, suggesting the protein kills white and red blood cells alike. According to the authors, their findings could have “important diagnostic significance.” They explain that because most diagnostic laboratories tend to use the same standardized growth medium and because most microbiology manuals already list A. actinomycetemcomitans as lacking beta hemolytic ability, the bacterium’s role in systemic disease may go undetected and thus be under reported. Based on their findings, the scientists propose taking a closer look at the bacterium’s hemolytic ability, particularly the key role of its leukotoxin in the process.