Classification of Bacteria based on Cell shape

Group - Description

• Cocci - Bacteria with spherical cells, 0•4 to 2um in diameter

• Diplococci e.g. streptococcus pneumoniae or pneumococci (found in human throat) - Adhere in pairs; gram positive ; non motile; capsulate; non sporing colonies in blood agar: 0•5  to 1mm in diameter, dome shaped (initially) surrounded by greenish grey halo

• Staphylococci e.g S. Epidermidis (found in normal human skin) - Adhere in grape like clusters; gram - positive; non motile; non sporing  colonies on nutrient agar: white or cream colour, entire edge and convex elevation , 2 to 4 mm in diameter

•  Streptococci e.g S.viridens (found on the upper respiratory tract ) - Adhere in long chains; gram positive, non motile; non sporing colonies on blood agar; 1 to 2 mm in diameter , surrounded by a narrow greenish grey halo

• Bacilli e.g Escherichia coli (found in intestines of humans and animals) - Bacterium with rod snapped cells, 1 to 10um long may occur singly or in chains; gram negative; some are motile; some are capsulate; non sporing Colonies on nutrient agar: 2 to 4 mm in diameter, opaque , convex, entire edge

• Vibrios e.g. vibrio cholera or comma bacillus (found in polluted water; causes cholera) - Bacterium is a rigid curved rod Gram negative ;motile; non sporing colonies on nutrient agar: 2 to 3 mm in diameter, whitish, translucent, low convex, entire edge

• Spirillae  e.g. spirrilium minor (found in rats) - Cockscrew shaped rigid bacterium Gram negative; motile (flagellum at each end).

• Spirochaetes e.g. Treponema pallidum (causes syphillis in humans) - Cockscrew shaped flexible bacterium cell is 10um long and 0•1 um in diameter with about 10 regular spirals; actively motile