Streptococcus salivarius

Streptococcus salivarius
Colony of Streptococcus salivarius on blood agar
Scientific classification
Domain:	Bacteria
Phylum:	Bacillota
Class:	Bacilli
Order:	Lactobacillales
Family:	Streptococcaceae
Genus:	Streptococcus
Species:	S. salivarius
Binomial name
Streptococcus salivarius Andrewes & Horder 1906
Synonyms
Streptococcus salivarius subsp. thermophilus Andrewes & Horder 1906

Streptococcus salivarius is a species of spherical, gram-positive, facultative anaerobic lactic acid bacteria^[1] that is both catalase and oxidase negative. S. salivarius colonizes (usually in chains) the oral cavity and upper respiratory tract of humans just a few hours after birth, making further exposure to the bacteria harmless in most circumstances. The bacterium is considered an opportunistic pathogen, rarely finding its way into the bloodstream, where it has been implicated in cases of sepsis in people with neutropenia, (a deficiency in white blood cells).

S. salivarius has distinct characteristics when exposed to different environmental nutrients. For example, in the laboratory, if a growth medium is used that includes sucrose then S. salivarius is able to use the sucrose to produce a capsule around itself. However, if sucrose is replaced by glucose as on a GYC (glucose, yeast extract, calcium carbonate) plate, S. salivarius is unable to make a capsule from the glucose.

More importantly, in the laboratory, S. salivarius can show a distinct clearing on GYC plates. This is because S. salivarius can ferment the glucose yielding lactic acid. Next, the lactic acid reacts with the calcium carbonate in the GYC plate, resulting in zones of clearings on the plate.[1]