Mycoplasmas are among the smallest cells known, with diameters of between 0.1 and 1.0 micrometres. These are perhaps the smallest organisms with enough DNA to program metabolism and enough enzymes and other cellular equipment to carry out the activities necessary for a cell to sustain itself and reproduce. Most bacteria are 1 to 10 micrometres in diameter, about ten times larger than mycoplasmas.
One of the primary differences between mycoplasmas and bacteria is the absence of a cell wall. Mycoplasmas lack the rigid cell wall of most bacteria; instead, they possess fluid lipid (water-insoluble fats) outer surfaces and, like tiny jellyfish, they can squeeze bend, and move into tight spaces. Their ability to take on many different shapes makes them difficult to identify, even under a high powered electron microscope.
Mycoplasmas are frequently referred to as being “somewhere between a bacteria and a virus”. They exhibit certain viral and bacterial behaviour. However, they can grow in tissue fluids (blood, joint, heart, chest, spinal fluid, etc.) and can grow inside any living tissue without killing the cells, as most bacteria and viruses will do.
When this stealth pathogen hitches a ride to other parts of the body, via the transit mechanisms set up through congested and faulty cellular communication pathways, it “shapes” itself according to the environment with which it seeks to blend, i.e. skin, blood, joints, central nervous system, liver, pancreas, cardiovascular, etc.
Mycoplasmas are well equipped to play biological sleight-of-hand, appearing then disappearing, changing shape, shuffling their surface components, ducking into cells, then parading as normal citizens of the human flora dressed in clothes stolen from the cells they invaded. They are elusive because they are pleomorphic (structurally changing).
Mycoplasmas evade the immune system by hiding inside host cells or fusing with the cellular membrane of the host cells. Certain pathogenic mycoplasmas can also invade lymphocytes and disrupt their functioning without provoking an immune response. Using “molecular mimicry,” mycoplasmas may even closely resemble host structures to fool the immune system into thinking that they are normal host cells, (rigid signals).