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Kristin Burkholder, Ph.D., assistant professor in the Department of Biology, along with 91ֱ����Ƶgraduates Zachary Tranchemontagne, M.S. (Biology, ’15), Ryan Camire, B.S. (Nursing, ’15), and Jessfor Baugh, B.S. (Medical Biology, ’13) and former staff member Vanessa O’Donnell (of the 91ֱ����ƵMicroscope Core Facility), wrote an article that was recently accepted for publication in the January 2016 issue of the journal Infection and Immunity.

According to the study, the bacterial skin pathogen methicillin-resistant Staphylococcus aureus (MRSA) can “trick” human immune cells into providing a safe place for its survival and replication. The researchers found that MRSA uses special virulence strategies to avoid being destroyed by macrophages, which are immune cells that normally engulf and kill bacteria.  As part of the typical immune response to infection, macrophages engulf microbes and enclose them within intracellular compartments called phagosomes, where the microbes are exposed to a deadly combination of antimicrobial enzymes and acids. 

The Burkholder laboratory’s work, spearheaded by lead author Tranchemontagne, demonstrates that after MRSA is engulfed by macrophages, the bacterium evades destruction by preventing phagosomal acquisition of antimicrobial enzymes and by responding to acidic conditions within the phagosome by upregulating expression of a key infection gene.  This allows the bacterium to survive and even replicate inside the very cells that are normally used by the body to kill pathogens. 

Since macrophages are long-lived cells that circulate throughout the body, the authors speculate that MRSA’s ability to survive inside of macrophages could contribute to infection persistence and bacterial spread from initial sites of infection, like the skin, to deeper tissues such as the bloodstream, heart or bones.

Tranchemontagne currently works as a Research Assistant III at the Wyss Institute at Harvard University, where he helps to develop new models, called “organs on chips,” for studying microbial infection.  Camire, who received the 91ֱ����Ƶ2015 Outstanding Undergraduate Researcher Award and the WCHP 2015 Maroon Award, now works as a Research Technician I in the Center for Immunology and Inflammatory Diseases at Massachusetts General Hospital and also takes courses at Harvard University to prepare for his application to M.D. /Ph.D. programs.  Baugh is a third-year student in the 91ֱ����ƵSchool of Dental Medicine.