Who’s Side Is Our Microbiota Really on When It Comes to Viruses?

Samantha Yohe (3 PM Micro) found a review article which further examines the beneficial role of the normal microbiota. In class, we described how these organisms can compete for nutrients with pathogenic microorganisms, and since they for the most part are better at doing this than pathogens, they can keep other bacteria, fungi, etc. from growing well. However, this model doesn’t really do much to explain the developing role of the normal microbiota in helping to prevent viruses from infecting us, since viruses do not need to compete for nutrients on their own. Here is Samantha’s summary:

Figure 1 from Wilks and Golovkina; overall stimulation of the immune system occurs due to the presence of the normal bacterial flora

After reading the article, Influence of Microbiota on Viral Infections from the NCBI website one isn’t sure about their resident microbiota’s intentions. Are these intentions good or are they bad?

Our normal flora is a significant variable when it comes to our current state of well-being. This flora has the opportunity to aid in the protection of our health against viral pathogens and much more. Microbiota coats the entry-ways of our body including skin, mucous membranes, and so on. It shows microbial antagonism making it difficult for a virus to wreak havoc on our system due to such an unwelcoming environment for the virus to flourish. But, our flora can have even more effects that help protect us from such infectious agents. One example from the article is that of mice and their susceptibility to the Influenza A virus. It was shown that mice treated with antibiotics that caused depletion of their natural commensals were more susceptible to the virus than those that were left untreated. This protection seen by commensals seems indirect according to researchers. The reason being is that the resident flora causes the release of inflammasome which in turn initiates migration of T-cells, the immune systems natural response to such infection.

The “dark side” to microbiota can show direct assistance in viral replication when looking at mice infected with oral poliovirus. In the article, mice were infected with poliovirus and some were treated then with antibiotics while others were left to fend it off with the aid of their normal flora. Results showed that those treated with the antibiotic had less of a mortality rate than those that were not. They also found that those mice treated by antibiotics still released the virus but its transmission ability was reduced. Researchers also found in their study that 3 viruses from 3 different families depended heavily on resident bacteria within the gastrointestinal tract of mice in order to reproduce. This quandary proposed another question to the researchers as far as human viruses go. HIV-1 is spread across our mucous membranes which are composed richly of commensal bacteria. Researchers question whether or not HIV-1 may be using our own flora to reproduce and transmit itself much like that of the poliovirus in mice.

The same researchers in this article also found that Mouse Mammary Tumor Virus (MMTV) uses immune response of Toll-receptors within the body of the infected mouse to create immunity for itself. MMTV was able to create its own immunity by taking advantage of the tolerogenic qualities of the normal flora of the mouse.

Now and for the rest of time clinical fields must remember the multitudes of bacteria that take up residence on and within our bodies and their interactions with numerous agents they come into contact with.  The interactions going on between our very own microbiota and these possible pathogens could mean the difference between protection and infection.

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About ycpmicro

My name is David Singleton, and I am an Associate Professor of Microbiology at York College of Pennsylvania. My main course is BIO230, a course taken by allied-health students at YCP. Views on this site are my own.

Posted on March 24, 2013, in Guest Post, Strange but True. Bookmark the permalink. Comments Off on Who’s Side Is Our Microbiota Really on When It Comes to Viruses?.

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