General Information: This organism causes arthritis in both rats and mice. Strains of Mycoplasma arthritidis can be virulent or avirulent depending, in part, on the presence of the MAV1 bacteriophage. This genus currently comprizes more than 120 obligate parasitic species found in the wide spectrum of hosts, including humans, animals, insects and plants. The primary habitats of human and animal mycoplasmas are mucouse membranes of the respiratory and urogenital tracts, eyes, mammary glands and the joints. Infection that proceeds through attachment of the bacteria to the host cell via specialized surface proteins, adhesins, and subsequent invation, results in prolonged intracellular persistence that may cause lethality. Once detected in association with their eukaryotic host tissue, most of mycoplasmas can be cultivated in the absence of a host if their extremely fastidious growth requirements are met.