How do we benefit from the microorganisms that live within us?

Hi everyone! A short while ago, I submitted an entry for a Cambridge Essay Competition titled, “How do we benefit from the microorganisms that live within us?” and I would like to share it with you:

Introduction:

Not all microorganisms are pathogens, yet the terms are often used synonymously. It is important to distinguish between the microbes that are beneficial, the pathogens that cause illness, and the commensal microorganisms that neither help nor harm. Being unaware of these categories and how to preserve the useful microbes can lead to choices that may have adverse effects on our health.

The human microbiota:

There are microorganisms found in most parts of the body. One of the most highly diverse communities of microbes are found on the skin. These make up the normal skin microflora. Many of the microorganisms living here are beneficial to the host as they are involved in protecting the skin against invasion. For example, Bacillus subtilis is a bacterium dwelling on the skin that produces a toxin known as bacitracin which acts as an antibacterial agent against other microbes. It has also been suggested that the skin microflora may be involved in enhancing the ability of T-cells to respond appropriately to pathogens[1].

A healthy microbial population in the reproductive tract is important to reproduce successfully as they have roles in gamete production, pregnancy and delivery of babies. Lactobacillus sp. is a bacterium found in the vagina that produces lactic acid – this is thought to be significant in lowering the pH of the environment which is a protective measure that prevents many infections and diseases including sexually transmitted diseases and urinary tract infections. In men, microbes have been discovered in lower parts of the genital tract which have a mixture of effects. For example, some unknown strains of Corynebacterium have been linked to prostatitis as they are abundant when an individual experiences the condition but decrease in concentration during treatment[2]. However, different species of coryneform bacteria form a large part of the normal microbiota which implies that most of these are either commensal or play a role in protecting against invading pathogens. It has also been suggested that interactions may occur between the microbiomes of the male and female genital tracts but there is not enough evidence to indicate this.

Most of the microorganisms found in the human body are in the gastrointestinal tract. There are thousands of different species of microbes in the human gut microflora alone.

Bacteroidetes and Firmicutes are the most abundant phyla in the gut, followed by Actinobacteria[3]. Bacteroides species, though have been described in the past to have a commensal relationship, where they do not have any effect, with the host, it has been suggested that it may be more accurate to describe it as a symbiotic relationship where both the bacteria and the human host experience benefits. An example of the advantages of Bacteroides is that they, along with other bacteria residing in the intestines, ferment carbohydrates forming fatty acids that can be used as a source of energy by the host. The energy gained from this contributes significantly to meeting part of the host organism’s energy demand. This has been demonstrated by experiments where the calories required to maintain body mass in germfree rats compared to normal rates was observed. The results show that the rats lacking a microbial population needed 30% more calories[5].

The abundance profile of microbes in the digestive tract have been shown to be affected by diseases such as obesity and inflammatory bowel disease. Though different studies contradict each other, a link has been suggested between the Firmicutes-Bacteroidetes ratio and obesity and some evidence shows that measuring this ratio in children can reveal predispositions to conditions like obesity later in life. Conducting further research to understand the mechanisms involved in this may allow the non-invasive manipulation of the microbiota of our gut to be used as a preventative measure or as part of treatment for weight-related health conditions[6].

Inflammatory bowel disease is a term used to describe a range of conditions where inflammation of the intestines occurs. While it is often categorised as an autoimmune disease, studies have suggested that it may be due to the immune system attacking the non-pathogenic microbes in the gut. This leads to inflammation which then causes injury of the bowel[7]. In patients with inflammatory bowel disease, the proportion of Bacteroidetes were shown to be significantly lower than the Actinobacteria and Proteobacteria concentrations[8]. The correlations between the abundance of microbes and the phenotypes of disease can allow us to hypothesise more accurately about the causes of the disease. However, it is currently unknown how inflammation and the microbiome influence each other. Nonetheless it is clear that trying to gain an insight into the mechanisms that connect the microbiota and inflammatory bowel disease could transform methods of diagnosis or even treatment of the disease. 

The microorganisms in the gut have a key role in the prevention of infections due to pathogens. For example, Clostridium Difficile is a pathogen and exists in small numbers in the bowel but does not cause harm as the other bacteria present there create a balance. Taking antibiotics when they are not necessary or using broad-spectrum antibiotics can disrupt this balance as many species of microbes may be wiped out by antimicrobials. The consequent decrease in the diversity and abundance of the gut microbiota means that pathogenic microbes are more able to flourish as the harmless microbes that use up the resources found in the intestines are less prevalent, so there is not as much competition[9]. In the 1900s, when it was observed that mice treated with the antibiotic streptomycin were more susceptible to infection due to Salmonella, the idea that intestinal microorganisms may have the potential to prevent invading bacteria to grow successfully, by a mechanism known as colonisation resistance, was recognised. Colonisation resistance can be divided into two categories: direct and indirect; direct colonisation resistance is where the microorganisms in the gut directly compete with exogenous pathogens for a resource, such as carbohydrates, or produce inhibitors that restrict the growth of particular pathogens. In indirect colonisation resistance, the intestinal microbes induce a specific immune response to target groups of invading microorganisms. For example, B. thetaiotaomicron can stimulate the host to produce certain types of antimicrobial substances[10]

The gut microbiota, aside from preventing pathogenic proliferation, helps in the development of the mucosal immune system. The presence of commensal microorganisms allows the immune system to become familiar with the antigens of many harmless microbes so that it can distinguish them from pathogens. The toll-like receptors in the membranes of lymphoid and epithelial cells in the small intestine are central to this process of recognition. The molecular patterns associated with harmless microorganisms such as the components of some bacterial antigens are recognised by these receptors and they promote tolerance to the constituents of a normal healthy microbiota.

In the womb, a foetus is thought to be germ-free – the baby’s first exposure to microbes is when it passes through the vaginal canal during birth. In order to prevent an acute inflammatory response which could harm the baby when it first encounters microbes, the receptors decrease their activity for a short period of time after birth to allow a microbial community to establish itself [11]. This may indicate that the body acknowledges the microbiota as necessary for the maturation of the immune system. The microbes in the nasal cavity, though little is known about them, may also have a role in determining immune response. 

Conclusion

There are a myriad of ways in which we benefit from the microorganisms that live within us. Due to its wide range of beneficial roles that are vital in maintaining our health, the microbiota of our body is sometimes referred to as an organ[12] and should therefore be treated with care. 

Bibliography

[1] Anil Kumar, Nikita Chordia (2017) Role of Microbes in Human Health [online]

Available at: https://www.omicsonline.org/open-access/role-of-microbes-in-human-health-2471-9315-1000131.php?aid=88460 

[Accessed on: 06/03/2019]

[2] Silver Türk, Sandra Mazzoli, Jelena Štšepetova, Julia Kuznetsova, Reet Mändar (2014) Coryneform bacteria in human semen: inter-assay variability in species composition detection and biofilm production ability [online]

Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3927743/ 

[Accessed on: 07/03/2019]

[3] Sai Manasa Jandhyala, Rupjyoti Talukdar, Chivkula Subramanyam, Harish Vuyyuru, Mitnala Sasikala, D Nageshwar Reddy (2015) Role of the normal gut microbiota [online]

Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4528021/ 

[Accessed on: 04/03/2019]

[4] Thryve editors (2018) The Layout of the Human Microbiota [online]

Available at:  https://blog.thryveinside.com/the-layout-of-the-human-microbiota/

[Accessed on: 04/03/2019]

[5] Hannah M. Wexler (2007) Bacteroides: the Good, the Bad, and the Nitty-Gritty [online]

Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2176045/#r208 

[Accessed on: 05/03/2019]

[6] Liene Bervoets, Kim Van Hoorenbeeck, Ineke Kortleven, Caroline Van Noten, Niel Hens, Carl Vael, Herman Goossens, Kristine N Desager,and Vanessa Vankerckhoven (2013) Difference in gut microbiota composition between obese and lean children: a cross-sectional study [online]

Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3658928/#__sec13title 

[Accessed on: 05/03/2019]

[7] Minesh Khatri, MD (2017) Inflammatory Bowel Disease [online]

Available at: https://www.webmd.com/ibd-crohns-disease/inflammatory-bowel-syndrome#1

[Accessed on: 06/03/2019]

[8] Jun Kim Ph.D. (2018) Inflammatory Bowel Disease And Microbiome [online]

Available at: https://blog.thryveinside.com/inflammatory-bowel-disease-and-microbiome/

[Accessed on: 06/03/2019]

[9] Elana Pearl Ben-Joseph, MD (2015) The Danger of Antibiotic Overuse [online]

Available at: https://kidshealth.org/en/parents/antibiotic-overuse.html

[Accessed on: 05/03/2019]

[10] Wikipedia contributors (2019) Colonisation Resistance [online]

Available at: https://en.wikipedia.org/w/index.php?title=Colonization_resistance&oldid=882815428

[Accessed on: 06/03/2019]

[11] Veronica Lazar, Lia-Mara Ditu, Gratiela Gradisteanu Pircalabioru, Irina Gheorghe, Carmen Curutiu, Alina Maria Holban, Ariana Picu, Laura Petcu, Mariana Carmen Chifiriuc (2018) Aspects of Gut Microbiota and Immune System Interactions in Infectious Diseases, Immunopathology, and Cancer [online]

Available at: https://www.frontiersin.org/articles/10.3389/fimmu.2018.01830/full

[Accessed on: 06/03/2019]

[12] Eisen J. (2012) Meet your microbes

Retrieved from: https://www.ted.com/talks/jonathan_eisen_meet_your_microbes/up-next

[Accessed on: 04/03/2019]

Leave a Reply

Your email address will not be published. Required fields are marked *