Bacteria are about 0.2-50 micrometers in size. Bacillus bacteria are 5×0.4-0.7 micrometers, Pseudomonas bacteria are 0.4-0.7 micrometers, and Micrococcus bacteria are about 0.6 micrometers. The smallest bacteria is Dialister pneumosintes. It causes disease in human respiratory tract. The largest bacteria is Epulopiscium fishelsoni. It lives as a parasite in the gut of a type of marine fish. Currently, Mycoplasma is considered as a bacteria.