Table 1.

Glossary of key concepts for interpreting microbiome research

Concept	Definition	Notes
Techniques for identifying microbiome components
Culture-based	Uses traditional techniques for culturing bacteria to determine which species are present	Some species (e.g., anaerobes) are difficult to culture; once cultured, definitive identification may be difficult
16S rRNA sequencing	Uses a conserved region of bacterial RNA to identify bacteria, combined with a species-specific sequence to determine which species are present	Unable to identify genes or presence of non-bacterial components (e.g., protozoa or fungi)
Metagenomic sequencing	Uses “unbiased” sequencing to determine all genes present in a sample and construct community structure; allows for determination of community composition and function	Remains relatively expensive, although cost has decreased; applications are still most suitable for research
Classification of microbiome composition
Abundance	Relative amount of specific bacterial groups in a sample	Most techniques only allow for determination of relative abundance of bacteria, not absolute (i.e., unable to determine total number of bacteria present in a sample)
α-diversity	Within-group microbiome diversity	Describes the makeup of a microbial community from one sample (e.g., one patient or one body site)
β-diversity	Between-group microbiome diversity	Allows for comparisons between groups of samples
Dysbiosis	Describes a microbial community that has been altered from its normal structure	Can be nonspecific; for example, unclear if this refers to decreased relative abundance of one group, decreased α-diversity, or another measure