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Weird Science: Bacteria Use Bleaching Agent to Cause Pneumonia

Hydrogen Peroxide Produced by Body is Double-Edged Sword

Bacteria can use hydrogen peroxide to weaken the immune system and cause pneumonia, according to a study at Umeå University and Stockholm University, Sweden.

By using hydrogen peroxide to defeat the immune system, the bacteria are “fighting fire with fire.” According to the researchers, as the body itself produces hydrogen peroxide as a defense against bacteria, “it was surprising to see that many types of bacteria actually use the same substance to overcome the body’s defenses.”

The researchers were primarily focused on Streptococcus pneumoniae, often called pneumococcus. It is the most common bacterium that causes pneumonia but it can also cause meningitis or severe sepsis. Pneumococcus can also pave the way for other microbes to attack, making it one of the world’s most deadly bacteria. At the same time, many people have the bacterium in their upper respiratory tract as a part of the normal flora without ever falling ill or knowing about it.

The ultimate goal of any invading microbe is to reside peacefully within our bodies without evoking a strong inflammatory reaction that might result in its elimination or cause us harm. Pneumococcus and other bacteria accomplish this, the researchers found, by targeting a key component of the immune system––the inflammasomes. Inflammasomes are protein complexes, which upon recognizing foreign molecules, e.g., those found in microbes or damaged cells, initiate reactions to kill microbes and clear diseased cells. Bacteria such as pneumococci release large quantities of hydrogen peroxide, which causes the inactivation of inflammasomes and thereby weakens the immune system.

In mice models, bacteria manipulated to produce less hydrogen peroxide were unable to inactivate inflammasomes and therefore elicited a faster inflammatory response that effectively cleared the bacteria from mouse lungs. The researchers also found that by inoculating the mice with catalase, a special enzyme that breaks down hydrogen peroxide, they could increase the inflammation and inflammatory symptoms, which led to a faster elimination of pneumococci from the lung.

Although inflammation often has negative connotations, for the body, it is an important process in the immune system’s defense against attacking microbes. Most microbes produce hydrogen peroxide to varying degrees, and the researchers’ studies demonstrate that hydrogen peroxide is an inhibitor of an important component of the inflammatory machinery. This suggests that “the mechanism we have uncovered is a common strategy employed by many microbes to thrive within us," says Saskia Erttmann, first author in the study.

Vitamins, including vitamin C, are one of the best-known substances for neutralizing hydrogen peroxide. This could boost anti-bacterial immunity, and lend credence to the old adage “an apple a day keeps the doctor away.”

Source: EurekAlert!, September 2, 2019

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