The virus helps the bacteria hide from the immune system


The virus helps the bacteria hide from the immune system

Together with the virus, the bacterium receives an enzyme that masks it from antibacterial antibodies.

Methicillin-resistant Staphylococcus aureus is one of the best known and most dangerous drug-resistant bacteria. (Photo: NIAID / View full size ‹ ›

Among the bacteria that live in our intestines, on the mucous membrane of the respiratory tract, on the skin, etc., there are those that usually do not cause any harm, but are potentially quite dangerous – if something happens, such bacteria can turn into a very serious infection. These bacteria include Staphylococcus aureus (Staphylococcus aureus). It can be found on the mucous membranes of the nose, mouth, and genitals as a harmless part of the local microflora. However, the same Staphylococcus aureus sometimes causes a number of diseases, from mild skin infections to pneumonia, meningitis and sepsis. Adding to the problems with it is the fact that some strains of Staphylococcus aureus have acquired widespread resistance to antibiotics – in particular, the well-known MRSA strain, which we have written about several times.

Why does Staphylococcus aureus suddenly start to behave badly? It is known that it actually constantly tests its host for strength, and if there is a gap somewhere in the defense, the bacterium turns from neutral to pathogenic. For example, staphylococcus constantly tries to increase its numbers, but the immune system does not allow it to do so. If it happens that immune vigilance weakens, the bacterium will quickly multiply to such an extent that it begins to pose a threat. Moreover, it must be taken into account that bacteria do not live alone, but in the company of many other bacteria. And the behavior of the same staphylococcus depends not only on its personal relationship with the immune system, but also on neighboring bacteria.

On the other hand, where there are bacteria, there are also bacteriophage viruses. It can be assumed that a virus that lives off the bacterium and weakens it will prevent it from starting an infection. However, as researchers from the University of Tübingen write in Nature, Staphylococcus aureus has a virus that actually helps it deceive its host defenses.

The immune system recognizes microbes by surface molecules that make up the cell wall. As is known, on top of the cell membrane, bacteria have a rather complex cell wall, the main component of which is polymer strands of peptidoglycan, forming a thick porous shell. The gaps in the peptidoglycan network are filled with a gel-like substance with teichoic acids – this gel helps the bacteria exchange substances with the environment. It is teichoic acids that the immune system “sees” with the help of antibodies. (Staphylococcus aureus is a gram-positive bacteria that has nothing else above the peptidoglycan wall; other gram-negative bacteria have another membrane above it.)

The authors of the work drew attention to the fact that the drug-resistant Staphylococcus aureus strain MRSA in its genome contains genes for enzymes that differently modify teichoic acids in the cell wall. Usually in staphylococci this is done by the enzyme TarS, but in some, another enzyme, TarP, is added to TarS, which pushes the usual TarS aside. It turned out that the second one comes into the bacterium along with the virus. Moreover, bacteria in which the viral enzyme worked managed to escape the immune system: the enzyme modified teichoic acids in such a way that the immune system stopped “seeing” them. Immune cells, when faced with such bacteria, destroyed them worse than bacteria without the viral gene.

The virus itself could once have borrowed a gene for a common enzyme from one of its hosts; then the enzyme changed slightly under the influence of mutations, and in a new form it became beneficial to both the bacterium and the virus, because if the immune system does not touch the bacterium, both parasites benefit from this.

So far, experiments have been carried out with cell cultures, and in the future it remains to be seen whether viral modification somehow affects the pathogenicity of the bacterium in a real living organism. If the virus really helps staphylococcus turn into a full-fledged infection, then one should think about how to turn off viral help in bacterial cells so that the immune system can detect and destroy them.

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Umar Coleman

Meet Umar Coleman, a professional with a wealth of experience in the realm of Linux administration and Unix systems. With a career spanning over two decades, Umar has honed his expertise as a Linux (Red Hat) admin since 2006, building on his earlier experiences with Unix systems from the 80s. Beyond his technical pursuits, he has ventured into radar research engineering and is also a dedicated teacher of Natural Family Planning. As a system administrator, Umar has been instrumental in ensuring the smooth operation of systems since 2005. With a passion for the web, he embraces hardcore web practices and excels as a social media specialist. A devoted music scholar, Umar constantly explores the diverse realms of music. As an entrepreneur, he pursues his ambitions while also indulging in his love for food as a wannabe food fan. In his leisure time, Umar enjoys gaming, immersing himself in captivating virtual worlds.