The Production Of Potent Cytotoxins By Streptococcus Pyogenes Contributes To The Severity Of 'Flesh-Eating Disease'

• comments
• 
• 

Beginning in the mid-1980s in the United States, Europe and other places, an epidemic of severe invasive infections caused by Streptococcus pyogenes (S. pyogenes) popularly known as group A streptococcus (GAS) occurred. The epidemic characterized by serious, fatal infections became commonly known by people as the "flesh-eating disease."

The production of potent cytotoxins by this human pathogen is said to contribute to the severity of the infection. However, a recent study suggests that the bacteria's full virulence is primarily dependent on the presence of two cytotoxins: the NADase (SPN) and the streptolysin O (SLO), according to Eurekalert.

Bacteria produce cytotoxins that are capable of leading to the death of cells and thus, result in infections of the deep fascia and other tissues, including necrotizing fasciitis. "Our research revealed that the most severe form of the disease requires two cytotoxins. If either one or both is missing, the infection is much less dangerous," lead author and chairman of the Department of Pathology and Genomic Medicine at Houston Methodist Research Institute, James M. Musser, MD, Ph.D., explained.

In order to investigate into how the toxins SPN and SLO act together, the researchers conducted an experiment on mice infected with genetically altered S. pyogenes strains that produced either or both of the toxins. Interestingly, they discovered that mutant strains that lack either SPN or SLO or both do not lead to severe forms of necrotizing fasciitis, bacteremia, necrotizing myositis, and other soft tissue infections.

The researchers found that the production of both toxins was necessary for full infection virulence. The resistance to bacterial infections partly depends on innate immunity conferred by white blood cells, including polymorphonuclear leukocytes. They also discovered that infections with SPN- and SLO-deficient S. pyogenes could be controlled better as it is less likely for it to resist the bactericidal effects of human polymorphonuclear leukocytes.

The Centers for Disease Control and Prevention (CDC), states that there are approximately 700 to 1,100 cases of necrotizing fasciitis caused by group A streptococcus which occurred yearly since 2010. While the disease mostly affects the young, the old and those who have underlying chronic conditions, it could also be seen in healthy individuals, according to Science Daily.

It can be transmitted from person-to-person and in most cases through a break in the skin. The findings of the study were published in The American Journal of Pathology.