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Streptococcus is a genus of gram-positive or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. [2] Cell division in streptococci occurs along a single axis, thus when growing they tend to form pairs or chains, which may appear bent or twisted.
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 encapsulated, Gram-positive, coccoid bacteria have a distinctive morphology on Gram stain, lancet-shaped diplococci. They have a polysaccharide capsule that acts as a virulence factor for the organism; more than 100 different serotypes are known, and these types differ in virulence, prevalence, and extent of drug resistance.
According to some definitions, the term is used to describe Gram-negative bacteria. [3] [4] According to other definitions, the term also encompasses yeasts. [5] [6] The name spheroplast stems from the fact that after the microbe's cell wall is digested, membrane tension causes the cell to acquire a characteristic spherical shape. [4]
Bacteria also live in mutualistic, commensal and parasitic relationships with plants and animals. Most bacteria have not been characterised and there are many species that cannot be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology.
Sucrose is the only sugar that bacteria can use to form this sticky polysaccharide. [1] However, other sugars—glucose, fructose, lactose—can also be digested by S. mutans, but they produce lactic acid as an end product. The combination of plaque and acid leads to dental decay. [12]
Later, in 1946, Lancefield described the serologic classification of S. pyogenes isolates based on components of their surface pili (known as the T-antigen) [13] which are used by bacteria to attach to host cells. [14] As of 2016, a total of 120 M proteins are identified. These M proteins are encoded by 234 types emm gene with greater than ...
Streptococcus thermophilus formerly known as Streptococcus salivarius subsp. thermophilus [2] [1] is a gram-positive bacterium, and a fermentative facultative anaerobe, of the viridans group. [3] It tests negative for cytochrome, oxidase, and catalase, and positive for alpha-hemolytic activity. [3] It is non-motile and does not form endospores. [3]