Streptococcus is a genus of bacteria that is spherical in shape. It grows in pairs or in chains (hence the cartoon). Multiple strains of Streptococcus are found as part of the normal microbiome – in the mouth, lower respiratory tract and the intestine. Whilst these do not cause a problem, some strains of Streptococcus (e.g. Streptococcus pyogenes) can cause inflammation.
Immunoglobulin A (IgA) is a type of antibody that is secreted in high amounts at mucosal surfaces – including the gut! It is important in defence against pathogens, stopping them from getting through the gut wall. It also has a complex role in regulating the commensal microbiome.
Cross-feeding is the process by which one type of bacteria utilises the breakdown products of a different type of bacteria. For example, the bacterium Bifidobacterium adolescentis breaks down sugars and produces acetate. A second bacterium, Faecalibacterium prausnitzii, then uses this acetate for its own growth and produces the short-chain fatty acid,