• lung cancer

The oral cavity is instrumental to the human body in several ways. It is the entry point for both ingested (to the GI tract) and inhaled (to the respirable tract) substances. The oral microbiome resides within biofilms throughout the oral cavity and forms an ecosystem that helps to maintain health. The breadth and depth of the oral microbiome is impressive: 1 mL of saliva contains 10⁸ microbial cells and 700 distinct prokaryotic taxa. There are rich communities such as bacteria, fungi, viruses, archaea and protists, among which about 54% are cultivatable and identified, 14% are cultivatable, but not identified, and 32% are not even cultivatable.1 Caselli et al defined the oral microbiome in 20 healthy individuals from Europe by whole genome sequencing (WGS) and reported that α-diversity differed significantly among the different microsites in the mouth of each participant, but not among the participants, supporting the notion of a recognisable healthy oral microbiome.1

With its rich microenvironment, the oral cavity remains less understood than the gut as to its health effects. Metagenomic studies have associated the oral microbiome with oral cancer and at least one with oesophageal cancer, and another with head and neck cancer.2

The use of recent 16 s rRNA gene next-generation sequencing methods have provided an important look into the complexity of the bacterial inhabitants of the oral microbiome and have helped to distinguish the differences between healthy microbiome and …