False-colour transmission electron micrograph (TEM) of a colony of the Streptococcus viridans group of bacteria, showing a typical paired formation. The viridans group includes the gamma & non-haemolytic streptococci; confusion exists over the taxonomic names of the various species. The viridans streptococci are the most common bacterial inhabitants of the oropharynx (mouth & throat) & can also be found in the gut & urogenital tracts. They may give rise to various human infections, including dental caries (tooth decay), endocarditis & abdominal abscesses. Magnification: x25,000 at 35mm size, x50,000 at 6x7cm size.