Wars between deadly bacteria and the immune system: new drugs are coming up

The Group A Streptococcus (strep) infections are usually caused by a particularly nefarious strain - M1T1. One of the reasons for this name is the type of tentacle-like M protein projecting from the bacterium's surface. Despite that a lot of studies before proposed ways M1 might contribute to strep virulence, researchers at University of California, San Diego School of Medicine and Skaggs School of Pharmacy and Pharmaceutical Sciences have given another explanation that is more persuasive than those ones: M1's ability to hold off antimicrobial peptides—natural antibiotics that comprise one of the immune system's front lines of defense.
The new study was published October 14 by Cell Host & Microbe. It emphasizes the importance of antimicrobial peptides, thus suggesting a new therapeutic approach to helping the immune system get rid of this crafty pathogen.
"The famous strep M1 protein has been shown to have numerous virulence properties that aid in bacterial colonization, fool the immune system or provoke inflammation," said senior author Victor Nizet, MD, professor of pediatrics and pharmacy. "We found that a major contribution of M1 protein to severe invasive infections can be explained by its ability to inactivate antimicrobial peptides."
More than 700 million infections all over the world each year, most notably strep throat and "flesh-eating" skin infections are caused by Group A strep. The body unleashes small antimicrobial peptides reacting to strep and other bacterial infections. These short chains of amino acids are deadly to bacteria in many ways such as summoning reinforcements in the form of infection-fighting cells or poking holes in bacterial membranes.
After research, the team found that Group A strep lacking M1 protein were easily killed by cathelicidin, a critical antimicrobial peptide. But they were rescued when armed with added M1 protein.
Besides, a research conducted on a mouse model showed that M49, a less virulent strain of strep, caused larger skin lesions in mice lacking cathelicidin than in normal, cathelicidin-producing mice. It means that M49 is unable to stiff-arm antimicrobial peptides the way M1 can, which makes the immune response more effective and the M49 bacteria less virulent.
The study stresses out the need to fortify or optimize antimicrobial peptides to improve the odds of defending infection of immune system. To know more about the interaction between M1 and antimicrobial peptides may develop new potential way of treating Group A infections. It's considerable to find an effective drug to help immune system fight against the infections by itself.
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