DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Coloured scanning electron micrograph (SEM) of Mycobacterium paratuberculosis, Gram-positive, rod prokaryote (dividing). Genetically M. paratuberculosis is almost identical to Mycobacterium avium. However phenotypically it grows much more slowly, requires an iron-transport chemical known as mycobactin for in vitro growth, forms rough colonies on solid agar media, and infects mammals instead of birds. M. paratuberculosis can grow only inside animal cells where it assimilates iron from its host's cells, most often immune cells called macrophages. Like other mycobacteria, M. paratuberculosis has the capacity to thrive inside macrophages. Thus, it is an obligate parasitic pathogen of mammals; a zoonotic microorganism that most commonly infects ruminant animals. Also associated with Johne's disease. Magnification: x3,000 when shortest axis printed at 25 millimetres.
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