Covert Tactics Used by Bacteria to Trick Human Immune System

Source: McMaster University

Summary: Comparing two strains of Salmonella – one that causes disease in humans and the other in reptiles, researchers discovered a covert way that the human-affecting bacteria essentially tricks the immune system into not attacking.

The immune system is very efficient at what it does, but if bacteria evolve ways to get around it, the immune response becomes ineffective. McMaster University researchers have found a new way bacteria evade the human immune system and promote infection. The team compared Salmonella Typhimurium, which generates disease in mammals, and Salmonella bongori, which is associated mainly with cold-blooded animals, particularly reptiles. While the two bacteria share a majority of their approximately 4,000 genes, the focus was on how those shared genes were regulated differently in the human pathogenic variants. They found that Salmonella Typhimurium has a mechanism wired into their genome that shuts down the expression of flagella once it contacts a host cell. The study findings were published in the journal Cell Reports.


Brian Comes in his lab at McMaster University. Credit: McMaster University

Researchers were surprised to discover that once the bacteria invaded into a host cell, it quickly turned off the flagella, making it difficult for the immune system to detect and respond. If you are bacteria expressing lots of flagella, it’s like wearing a neon sign around your neck basically alerting the immune system to your presence. Salmonella Typhimurium is disease-causing bacteria predominately found in the intestine. The Coombes lab is building on these findings by searching for new ways to bolster the immune system. Coombes noted that understanding how bacteria become harmful assists McMaster University’s research focus on helping address the looming antibiotic resistance crisis.

Prof. David Coombes said, “This research is important because it opens up new targets for drug discovery”, “If we can figure out the mechanism of how Salmonella shuts down flagella, and if we can figure out how to reverse that, we can boost the immune system. The immune system will do what it’s naturally evolved to do, which is detect the presence of the bacteria and gain the upper hand.”

More Information: Sarah L. Jaslow et al, “Salmonella Activation of STAT3 Signaling by SarA Effector Promotes Intracellular Replication and Production of IL-10”, Cell Reports (2018). DOI:

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