Combat Bugs in your Gut
Amanda Whitling
May 19, 2011


It is well known that the microbiota located in your intestines helps control pathogen colonization. This is better known as colonization resistance, or CR, which helps protect against enteric pathogens. There are three mechanisms that contribute to colonization resistance aiming to combat the pathogen colonization in the gut. The three ways of helping control pathogen colonization in the intestine include direct inhibition of pathogen growth by microbiota, microbiota-induced stimulation of innate and adaptive immune responses, and the depletion of nutrients by microbiota growth.

Normal microbiota both harms the body and works to benefit the body in such ways as combating bugs in your gut! Normal microbiota, also known as normal flora, protects the body by preventing the overgrowth of harmful bacteria (Tortora, 18). Normal microbiota is crucial to the large intestine as they out-compete bacteria for nutrients and inhibit invading bacteria. It is important that normal microbiota exist in the intestine; if they are completely depleted, the intestines are at high risk for invasion of bacteria and are susceptible to infectious disease. Food intake and pathogen infection are environmental factors that microbiota interact with in the large intestine (Stecher). This topic was of interest to me, because it explains the positive effects that microorganisms and bacteria have on our bodies. Intestinal microbiota is essential in protecting our bodies from pathogen colonization.

There are about 400 different obligate anaerobic bacterial species that are a part of the human intestinal microbiota. Some phyla included in this intestinal microbiota include Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria, Fusobacteria, Verrucomivrobia, and Cyanobacteria.

The intestinal microbiota is normally beneficial rather than harmful as they help limit pathogenic bacterial infections. Microbiota helps the development of lymphatic tissues and the mucosal immune system, and it controls the metabolism of the host. There are three mechanisms microbiota exert to fight the infection of pathogens:
1. Direct Inhibition – Microbiota obstruct pathogen growth with its release of inhibitory metabolites and bacteriocins (proteins that inhibit the growth of other bacteria of the same species) so infection cannot occur - this is colonization resistance.
2. Nutrient Depletion – Normal microbiota in the intestine deplete a majority of nutrients that maintain the growth of pathogens.
3. Stimulation of immune responses – the host’s innate and adaptive immune defenses. As an infection is ending, pathogens are eliminated from the gut lumen, where they attempted to replicate and cause disease. Defensins are responsible for this as they are secreted into the gut lumen, creating a barrier, and therefore providing protection.


However, sometimes microbiota expresses harm to the human gut with diseases such as inflammatory bowel diseases (IBD.) IBD may occur if barrier functions deteriorate or signal pathways of innate or adaptive immune system fail (Stecher).

Diets can also alter the intestinal microbiota; some may alter their diet to attain favorable microbiota in hopes of enhancing colonization resistance.

Literature Cited:

Kucik, Corry Jeb, Gary L. Martin, and Brett V. Sortor. Common Intestinal Parasites. Published online in American Family Physician Vol 69, Issue 5, pp 1161-1169 (2004).

Lane, A. Jonathan, Raj K. Mehra, Stephen D. Carrington and Rita M. Hickey. The food glycome: Asource of protection against pathogen colonization in the gastrointestinal tract. Published online in International Journal of Food Microbiology Vol 142, Issues 1-2, pp 1-13 (2010).

Palmer, Chana, Elisabeth M. Bik, Daniel B. DiGiulio, David A. Relman, Patrick O. Brown. Department of the Human Infant Intestinal Microbiota. Published online inPLoS Biol 5 (7): 177 (2007).

Stecher, Barbel and Hardt, Wolf-Dietrich. Mechanisms Controlling Pathogen Colonization of the Gut. Published online in Current Opinion in Microbiology Vol. 14 Issue 1, 82-91 (2011).

Tortora, Funke, Case. 2010. Microbiology: An Introduction. Pearson Education Inc. Ca. pp. 812.

Vollaard, E.J. and Clasener, H.A.L. Colonization Resistance. Published online in American Society for Microbiology, pp. 409-414 (1994).