Streptococcus pyogenes is the microbe behind the rare disease, necrotizing fasciitis. These Gram positive bacteria, which are also the cause of strep throat, are found in a cocci arrangement of long bead like chains. Streptococci are non-spore forming and non-motile, and are capable of forming capsules and slime layers. They are facultative anaerobes that ferment a variety of sugars. As do many bacterial pathogens, these organisms secrete unique exoenzymes, or toxins, that help them avoid host defenses or promote multiplication in tissues. Streptococcus pyogenes produces a streptokinase that digests blood clots and apparently assists in the invasion of wounds. It produces a protease that accounts for the severe form of "flesh eating" disease. Proteins attached to the outer portion of the cell wall also have toxic properties.
Infection is generally transmitted through direct contact, droplets, and in some cases food. The disease begins with the bacterial invasion of a small cut or abrasion and then spreads to the dermis and subcutaneous tissue. The streptococci begin to multiply rapidly. The strains of group A streptococci, responsible for necrotizing fasciitis, have greater toxigenicity than typical strains of S. pyogenes due to the release of the specialized exoenzymes and toxins. These enzymes digest the connective tissue and the toxins poison the epidermal and dermal tissue. As the flesh is killed, it separates and sloughs off, forming a pathway for bacteria to spread to deeper tissue, including muscle. The infection becomes more serious if it is mixed with other anaerobic bacteria. Streptococcus pyogenes is not highly resistant and therefore can be treated effectively if detected early on.
Group A streps have been implicated in the type of toxic shock responsible for the death of Muppet creator Jim Henson. Also, the bacteria were the cause of several childhood deaths in California, in which chickenpox lesions were infected by the streptococci. Currently, in Texas this "killer bacteria" is making headlines. The epidemiology associated with this so called "flesh eating disease" is somewhat mysterious. The number of infections declined dramatically following the discovery and active use of antibiotics, but in more recent times isolated cases have been found in increasing numbers. Bacteria isolated from the Rocky Mountains and the East Coast appear to be new, more virulent strains. It is theorized that the newer strains are mutants that have acquired toxin genes from infecting viruses.
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.
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