As humans, our perception of “germs” begins early, when our parents teach us to wash our hands, cover our mouths when we cough, and not eat after other people to avoid “catching something.” These behaviors serve important functions in preventing sickness. Over time, we come to understand that these germs are microorganisms known as bacteria and viruses.
Since the identification of the first bacteria, research has primarily focused on characterizing the ways in which bacteria cause disease. These studies were fundamental in establishing ways that we prevent and treat infections. This research also revealed that bacteria are naturally found on our skin and in our noses, mouths and respiratory, gastrointestinal and urogenital tracts.
The bacteria that live within us make up our microbiota. Some microbiota cause disease, while some microbiota bacteria are “good” and beneficial. Such good bacterial species have established a commensal relationship with humans, in which the bacteria do not make us sick, and we provide a home for them to grow in.
The National Institutes of Health started funding the Human Microbiome Project in 2007. The research focus of the scientists awarded this money was the sequencing of the genomes of our microbiota, termed the microbiome. This project resulted in a DNA database of nearly every bacterial species in the human microbiota and marked the emergence of a large amount of recent scientific research that focuses on the role of the “good” bacteria found in our bodies.
The majority of research has focused on the gut (gastrointestinal) microbiota, which includes bacterial species such as the Bacteroides, Clostridium and Lactobacillus. Nutrition, age and lifestyle influence which bacterial species are present in the gut, which directly impacts our health. Some bacterial species present in the gut aid in the digestion of complex sugar molecules. Bacteria then use the sugar components to produce molecules that help develop and maintain our immune system and impact our nervous system. Gut bacteria also produce nutrients and vitamins (such as Vitamin K) for use by human cells. These interactions are very important for the maintenance of human health, as there is an association between changes to the species present in the microbiota to diseases such as irritable bowel disease (IBD), type 2 diabetes, obesity, allergies and autoimmune disorders.
Microbiota from multiple locations within the human body also protect us from infection by more serious pathogenic bacteria. The commensal bacteria compete with pathogenic bacteria for nutrients and colonization spaces, which helps control the growth of pathogenic bacteria.
More research is needed to fully understand the health effects when the composition of the microbiota is disturbed, such as through antibiotic treatment. Current treatments for microbiota disturbances can include fecal transplants and dietary modification with prebiotics (substances that promote growth of beneficial bacteria) and probiotics (live cultures of commensal or “good” bacteria). Exactly how, or even if, these treatments restore or maintain the commensal balance is not known.
Particularly, the use of probiotics has gained popularity for the treatment or prevention of potential illnesses and the general maintenance of health. Humans have several options available to consume probiotics, including various drinks, foods such as yogurt or even pills. Each method of consuming probiotics varies in the specific mixtures of probiotic strains that they contain, depending on the manufacturer. While some individual bacterial strains have been associated with the various health or disease states discussed above, the effectiveness of treating disease conditions or a disturbance of the microbiota species with a mixture of commensal bacteria is not known. While our understanding that the microbiota has a role in maintaining human health has increased in recent years, more research is needed to fully understand how the microbiota presence (in its natural state or from the result of probiotic treatment) or absence contributes to our health or disease states.