Mycoplasma sp. Coloured Transmission Electron Micrograph of a negatively-stained Mycoplasma sp. cell. This cell is a dumb-bell shape (orange) with vesicles emerging from either end. Mycoplasma are the smallest cellular organisms known (diameter 0.3-0.9 microns). They are similar to primitive bacteria but the lack of a true cell wall means they are found in a variety of shapes. Mycoplasma pneumoniae causes a pneumonia-like disease of the human lungs. It is probably the most common cause of pneumonia in adults and accounts for 10- 30% of acute lower respiratory tract infection. Mycoplasma also cause pneumonia in animals. Magnification: x50,000 at 6x4.5cm size. x200,000 at 7x9ins