Killing bacteria by simple contact

To protect the human body from bacterial infection, immune cells must be able to eliminate pathogens. The predominant mechanism involves ingesting bacteria. However, certain immune cells, neutrophils, appear to have the ability to kill bacteria without ingesting them.


Simple contact may be enough to kill bacteria

In order to gain a better understanding of this still partly mysterious mechanism, scientists in Prof. Pierre Cosson's laboratory looked into the destruction mechanisms of the Pseudomonas aeruginosa bacterium, which is known to cause serious respiratory infections. Their work, published in the journal Molecular Microbiology, enabled them to confirm the existence of bacterial destruction mechanisms without ingestion. Experiments conducted with the immune cell model Dictyostelium discoideum revealed that when Dictyostelium discoideum (white silhouette in the videos below) detects a bacterium in its environment, it can establish a simple contact that is sufficient in the majority of cases to kill it, either during the contact (video on the left) or a few minutes later (video on the right).

When the immune cell model  Dictyostelium discoideum (white silhouette) detect a bacterium (in green) in its environment, it can establish a contact with it, which is sufficient in the majority of cases to kill it, either during the contact (left-hand video), sor a few minutes later (right-hand video). Adapted from the Figure 4 in Ayadi et al. 2023.


To discover the genes involved in this mechanism, the scientists tested mutants of their immune cell model. This approach revealed that the AplA protein plays a crucial role in eliminating bacteria outside the cell. Once secreted by the cell, AplA seems capable of perforating the membrane of bacteria, leading to their death.


What's next ?

These results confirm the existence of mechanisms for destroying bacteria, independently of their ingestion. The research team is now working to understand how certain bacteria manage to survive despite close contact with immune cells. This work should open up new avenues in the fight against bacterial infections.


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8 Dec 2023