The term microbiome was coined by Dr. Joshua Lederberg and refers to an ecological system of commensal, symbiotic and pathogenic microorganisms that reside in the human body (Lederberg & Mccray, 2001). Microbiome and microbiota are interchangeable words, microbiome refers to the collection of genomes from all microorganisms in the environment, that includes microbial elements, metabolites and environmental conditions. On the other hand, microbiota refers to living microorganisms found in specific environments like oral or gut microbiota. Since phages, viruses, plasmids, prions, viroids, and free DNA are not considered live microbes, they are excluded from microbiota. Contrary to this microbiome refers to both microorganisms and their synthesized metabolites (toxins, polysaccharides, signaling molecules) and structural components (nucleic acids, proteins, lipids).

Despite being microscopic, they play a vital role in human health. A healthy individual comprises both beneficial as well as hazardous microbes that make up its microbiome. An imbalance between these can result in dysbiosis leading to several disease conditions and the body might become more susceptible to illness.

Irrespective of whether bacteria are part of the microbiome or not, they prefer to live in a community called biofilm. They must interact with each other to form a community and this is facilitated by small molecules called autoinducers. Quorum sensing is used to count the number of ‘self’ in the community and determine whether other bacterial species are present (Frederix & Downie, 2011). Fig. 1 explains the mechanism of quorum sensing.

The microbiome resides in various regions of human body such as the Gastrointestinal (GI) tract, nostril, skin, hair, vaginal and oral cavity, and is associated with several disease conditions such as eczema, gastric ulcers, Cardiovascular disease (CVD), and cancer. The disturbance can result in disruption to the natural balance of the microbiome, whereas in other cases, the presence of certain microbial communities might either directly induce illness or foster a favorable environment for pathogenic activity (Thomas & Jobin, 2015).

The microbiota network depends on genetic composition and is different for every individual. The first exposure to microbes is through the birth canal followed by the mother’s milk after delivery. The microbiome of an infant correlates with that of its mother but can change as a result of subsequent nutrition and environmental exposure which may either promote health or make an individual more prone to illness.

Compared to microbiomes at other body regions, the bacterial species at gut microbiome are more diverse. Nearly 3000 different bacterial species have been identified from human faeces, based on information gathered by the Human Microbiome Project and the metagenomic research database MetaHIT. The species have been divided into 11 distinct phyla, among which Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes comprises more than 90 % of the gut microbiome (Huttenhower et al., 2012).