Current Affairs 11th Class

Category : 11th Class

They are gram negative obligate pleomorphic but walled obligate intracellular parasites which are transmissible from arthropods. They are intermediate between true bacteria and viruses. Rickettsias require exogenous factors for growth. Cell wall is like typical bacterial wall. ATP synthesis is absent but ADP is exchanged with host cell ATP. They have genome and size (0.3-0.5\[\mu m\]) smaller than true bacteria but have a longer generation time. Internally the cells of rickettsias contain DNA as well as RNA in a ratio of 1 : 3 .5. The cell walls contain muramic acid and are sensitive to lysozyme. Flagella, pili and capsule are absent. Reproduction occurs by binary fission. The natural habitat of rickettsiae is in the cells of arthropod gut. They cause typhus group of fevers. Spread by droplet method, lice, ticks, fleas, etc.

Human diseases