Bacteria are everywhere, including in the human body where it plays an important role in our health. Your bacterial ecosystem, referred to as your microbiota helps protect us from infections. In an article in Infection Control Today (summarised below) , Austin Yan discusses how we came to realize the importance of our microbiota, how it helps our immune system, and how this microbial defence system may be at risk (http://infectioncontrol.tips/2015/11/13/fighting-infections-in-a-microbial-world/
The Age of Bacteria
The dinosaurs, in over 150 million years of prowling, were just a passing phase for our fellow microbes. In a world of microbes, we’re just new arrivals.
W now understand that while there are “bad” bacteria, or pathogens, there were also “good” bacteria, or commensals. These bacteria, which vary from person to person, help digest complex nutrients, prevent common gut diseases, and improve our immune system. The influence of our microbial ecosystem on our health led to our microbiota being described as a “forgotten organ”.
Your ecosystem of a hundred trillion bacteria serves many important functions, including its key role in nutrient metabolism that contributes to overall health. But these bacteria are also critical in defending the body from infections. These effects are mediated in two main ways: blocking pathogen growth and training the immune system.
Simply by being present, your microbiota is a deterrent preventing pathogens from moving in. These commensals establish dominance by colonizing ecological niches and producing compounds called bacteriocins that are toxic to other bacteria.
Having a bacterial community established throughout your body is among the first line of defense against pathogen invasion. This explains why antibiotic therapy, which eliminates a lot of the resident microbes, makes individuals more prone to invasions by Clostridium difficile, an infection that causes severe diarrhea. In reality, the distinction between good and bad bacteria is less clear, as some commensals may proliferate and “go rogue” if given the opportunity. Bacteria like C. difficile, which may be present in small numbers in a healthy individual, kept in check by its neighbouring bacteria, may become pathogenic if the gut microbiome is disturbed e.g by amtibiotics.
Our gut microbes also play a role in immune system development. Our immune system directs our body’s response against pathogens, but fails us when it overreacts, causing an undesired immune response, or under reacts, allowing pathogens to invade. The microbiota is able to fine-tune our immune response, first by training our immune system to become more tolerant to its bacterial population. Not only does this tolerance prevent attacks to our commensal bacteria, this training also suppresses allergic reactions and reduces the chances of developing autoimmune conditions like Crohn’s disease.
Also, by fine-tuning our immune system to recognize resident microbes, the body is sensitized to targeting foreign invaders.
Like any part of our body, our microbiota can be compromised, making us more vulnerable to immune diseases and infection. The developed world has seen a marked increase in conditions like asthma and allergies, which has been attributed to a reduction in microbial exposure.
It is suggested that the deterioration of our microbial ecosystem to modern medicine. Our extensive use of antibiotics and increased reliance on elective Caesarean deliveries, which prevents newborns from being exposed to their mother’s vaginal microbiota, have led to reduced diversity in our microbial communities and a loss of certain bacterial strains that may have protective effects.
So what can we do to maintain our microbial defenses? Most importantly, being aware of our microbiota allows us to be more informed about our health care decisions. For example, avoiding overuse of antibiotics. Other treatments, including probiotics and prebiotics, are also being developed to introduce good bacteria into our gut and maintain a stable, healthy microbiota.