''Streptococcus mitis'' is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

Gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. The Gram stain is ...

mesophilic A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, with an optimum growth range from . The optimum growth temperature for these organisms is 37 °C (about 99 °F). The term is mainly applied ...

, alpha-hemolytic

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

in the genus ''

Streptococcus ''Streptococcus'' is a genus of gram-positive spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. Cell division in streptococci occurs along a sing ...

'', belonging to the viridans streptococci group. These bacteria are facultative anaerobes, and made up of non-motile and non-sporing

cocci Bacterial cellular morphologies are the shapes that are characteristic of various types of bacteria and often key to their identification. Their direct examination under a light microscope enables the classification of these bacteria (and archaea ...

(round cells) that are catalase negative. It is a

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit f ...

and commonly inhabits the human mouth, throat, and upper respiratory tract, as part of the oral microbiota. They are clinically important for humans, as under certain conditions, it can cause opportunistic infections, such as

infective endocarditis Infective endocarditis is an infection of the inner surface of the heart (endocardium), usually the heart valve, valves. Signs and symptoms may include fever, petechia, small areas of bleeding into the skin, heart murmur, feeling tired, and anem ...

Classification

Members of the ''

'' genera belong to

lactic acid bacteria Lactobacillales are an order of gram-positive, low-GC, acid-tolerant, generally nonsporulating, nonrespiring, either rod-shaped (bacilli) or spherical ( cocci) bacteria that share common metabolic and physiological characteristics. These bact ...

defined by the formation of

lactic acid Lactic acid is an organic acid. It has the molecular formula C3H6O3. It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as wel ...

as an end-product of

carbohydrate metabolism Carbohydrate metabolism is the whole of the biochemistry, biochemical processes responsible for the metabolic anabolism, formation, catabolism, breakdown, and interconversion of carbohydrates in life, living organisms. Carbohydrates are central t ...

. The family ''

Streptococcaceae Streptococcaceae, from Ancient Greek στρεπτός (''streptós''), meaning "twisted", and κόκκος (''kókkos''), meaning "sphere", are a family of gram-positive bacteria, placed within the order Lactobacillales. Representative genera i ...

'' is characterized by based upon its

16S rRNA 16S ribosomal RNA (or 16Svedberg, S rRNA) is the RNA component of the 30S subunit of a prokaryotic ribosome (SSU rRNA). It binds to the Shine-Dalgarno sequence and provides most of the SSU structure. The genes coding for it are referred to as ...

gene sequence analysis within the low (< 50 mol%) G+C branch. There are over 50 species in the genus which are classified by their 16S rRNA sequences.

Habitat

''Streptococcus mitis'' primarily resides in the oral cavity which includes the mouth,

nasopharynx The pharynx (: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates, though its ...

, and throat. However, there have also been cases of it in the female genital tract, the gastrointestinal tract, and even on the skin.

Natural genetic transformation

''S. mitis'' is competent for natural genetic transformation. Thus ''S. mitis'' cells are able to take up exogenous DNA and incorporate exogenous sequence information into their genome by

homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in Cell (biology), cellular organi ...

. These bacteria can employ a predatory fratricidal mechanism for active acquisition of homologous DNA.

Moon Surveyor 3 probe

Approach

It has been reported that ''Streptococcus mitis'' identified and survived for over two years on the Surveyor 3 probe on the Moon. However, NASA stated that this is most probably due to contamination upon return to Earth. The

Apollo 12 Apollo 12 (November 14–24, 1969) was the sixth crewed flight in the United States Apollo program and the second to land on the Moon. It was launched on November 14, 1969, by NASA from the Kennedy Space Center in Florida. Commander Charles ...

crew received pieces of Surveyor in 1969, one of these was the TV camera. The probe was then analyzed to consider how the lunar environment affected the material. Surveyor 3 had not been sterilized before its launch because scientists wanted to see if organisms could survive the two and half years on the Moon, so looking for surviving organic material was a part of this analysis.

Results

Upon inspection, a group found an amount of ''S. mitis'' inside a piece of foam located inside the camera. Culture plates were made and the identity was later confirmed as ''Streptococcus mitis'' at the US Communicable Disease Center at Atlanta, Georgia. At first, it was speculated that ''S. mitis'' had been picked up from the Moon but research later discovered that the residence of the bacteria on the probe had started after the probe returned.

Characteristics of ''Streptococcus mitis''

References

External links

S. mitis subdural empyema
from MedPix
Type strain of ''Streptococcus mitis'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
Streptococcaceae Gram-positive bacteria {{Bacilli-stub