Bacteria are classified as given below:
(i) Cocci : They are oval or spherical in shape. When they occur singly, they are called Micrococcus; if in pairs Diplococcus; if in a chain, Streptococcus; and if occur in clusters, Staphylococcus.
(ii) Bacilli: They are rod-like, with or without flagella. Flagella may be present at one or both the ends or around cells. Bacteria may occur singly, Bacillus; or in pairs, Diplobacillus or may form filaments, Streptobacillus.
(iii) Vibrio : They are small and curved like commas. These are mostly motile.
(iv) Spirillum : These are twisted like a screw. They have flagella at one end or both the ends. Certain bacteria possess flagella for locomotion.
