Streptococcus pyogenes bacteria. (Image: CDC)

Researchers at the University of California San Diego have taken a significant step forward in the effort to develop a vaccine against the bacteria responsible for strep throat, toxic shock syndrome, and flesh-eating disease.

Group A Streptococcus, or group A strep, are nasty breed of bacteria that can cause an assortment of infections. Most group A strep infections are relatively mild, such as strep throat and the impetigo skin infection, but occasionally these bacteria go on to cause more serious and even life threatening conditions, such as toxic shock syndrome and necrotizing fasciitis, or “flesh-eating disease.” According to the CDC, around 500,000 people die each year from this bacteria, prompting researchers to find novel ways of staving off these dreaded germs.

In a new study published in Nature Microbiology, a group of researchers from the University of California San Diego have detected previously unseen patterns in the outer protein coat of group A strep. These hidden sequence patterns, called the M protein, limit the body’s immune response against these bacteria. It’s an important piece of insight that shows why the human body is so vulnerable to this bacteria—and how we might be able to develop a vaccine to compensate.

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“When we become infected with a particular strain of group A Strep, we generally mount an immune response against the particular M protein displayed by that strain,” explained lead researcher Partho Ghosh in a statement. “But this immunity works only against the infecting strain.”

Ghosh says the bacteria mounts a disguise, leaving us vulnerable to infection by other group A strep strains with other types of M proteins. “This is because the antibody response against the M protein is almost always specific to the sequence of that M protein, and M proteins of different types appear to be unrelated in sequence to one another,” Gosh said.

Insidiously, strep A bacteria uses our own body against us, recruiting a human protein called C4BP which tricks the body into calling off an immune response. But practically all M proteins can bind to C4BP, so if the researchers can develop an antibody that does the same thing, they will have found a way to destroy the otherwise invisible bacteria.

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To see if this is indeed possible, the researchers conducted an experimental computational study. The biochemists recreated four crystal structures of four different M proteins—and like lego blocks, each of these structures attached themselves to human C4BP.

“The idea now is to have antibodies do the same thing as C4BP—that is, recognize many different M protein types,” said Ghosh. Assuming this can be done, the researchers will engineer an antibody response that’s not limited to one M protein and one strain of group A strep. And in fact, it could extend to practically all M protein types and strains of group A strep.

It may be years, if ever, before we see this vaccine reach the market. Until then, we can do some practical things to help prevent group A infections. The CDC recommends hand washing, especially after coughing and sneezing, and before preparing foods or eating. People with sore throats should visit their doctor, and if the tests reveal strep, they should stay home from school or work at least 24 hours after starting antibiotics. As for wounds, they should be kept immaculately clean and observed for signs of infection, such as redness, swelling, drainage, and pain. Should any of these signs appear, it’s advised that you see a doctor immediately.

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[Nature Microbiology]