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New insights into staph aureus re-infection

Researchers have discovered new insights into how staph bacteria elude the immune system, knowledge that could guide research into new avenues of therapy for the prevention of drug-resistant infections.

The findings come from a paper published online in Cell Host & Microbe (Sept. 21, 2017).

Widespread MRSA infections have prompted routine use of antibiotics that were once considerd last-line, and this is making the antibiotic resistance problem worse, co-lead author Dr. George Liu, said in a press release.

Dr. Liu is a pediatric infectious diseases physician at the Cedars-Sinai Medical Center’s Maxine Dunitz Children’s Health Center, and the F. Widjaja Foundation Inflammatory Bowel and Immunobiology Research Institute in Los Angeles.

“Our study focuses on why MRSA is so common and why we never develop immunity to these bacteria,” he said.

Typically the immune system learns to recognize key proteins from a pathogen, so can respond to future infections more quickly. But the human body can have repeated staph infections throughout life without developing a robust protective memory immune response.

This study shows that staph bacteria are able to dodge this immune response, as the bacterial cell walls of Staph. aureus do not break down and expose proteins that can be recognized by immune cells, so the body does not produce a defence against future exposure.

“Essentially, staph tricks the body’s T cells, which are white blood cells that fight infection, and prevents them from mounting an effective defense,” said co-lead author Dr. Gislaine Martins, an assistant professor at the F. Widjaja Foundation Inflammatory Bowel and Immunobiology Research Institute and departments of Biomedical Science and Medicine at Cedars-Sinai.

“The study explains why our immune system is fooled by staph,” Dr. Martins said. “Staph evolved to have this enzyme that makes this modification in its cell wall. This modification protects the wall from degradation and therefore from being properly detected by the immune system, which won’t remember the bacteria the next time the body is infected.”

When investigators modified staph to lack this enzyme that protected its cell wall, the staph cells more easily spilled their molecular contents, and spurred a robust memory immune response in a mouse model that protected against reinfection.

The authors suggest that the findings provide clues about how to develop staph vaccines to make them more effective. Most staph vaccines that have been previously tried have attempted to stimulate antibodies—specialized molecules that recognize foreign bodies and help to mobilize the immune system. This study suggests that a successful vaccine should harness the body’s T cells, according to the release.

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