False colour transmission electron micrograph (TEM) of Streptococcus sp.,showing a bacterium in the final stages of division by binary fission. Genetic material in daughter cells appear white. Streptococci are Gram positive,non-motile,non- sporing and are recognized by a tendency to form chains. They occur as parasites of man and animals,contributing to the normal,healthy flora of human respiratory,alimentary (gut) and female genital tracts. Some species are pathogenic to humans,including S. pneumoniae and S. pyogenes,although both species also occur as commensals (ie deriving nourisment from a host without causing harm or benefit). Magnification: X 12,000 (35mm) |