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A number of features are used to identify bacteria. The shape of an individual cell is important and enables it to be classified as a bacillus, a coccus, a spirillum or a vibrio.

Bacilli o r rods Cocci

o r in ir re g u la r c o lo n ie s

Salmonella typhi causes ty p h o id fe ve r Bacillus subtil is is used in genetic eng ineering

o r in cha ins

Staphylococcus aureus causes boils

Streptococcus lactus is used in m aking cheese

Spirilla Vibrios o r curved rods

Treponema pallidum causes Vibrio cholerae causes cho le ra syphilis

Identifying bacteria by the ir shapes


With their small size and the enormous number of species involved, shape alone is inadequate as a means of identifying individual bacteria. The molecules that they contain and the biochemical processes within their cells are also important and allow techniques such as Gram's staining to be used to distinguish among bacteria that look very similar under a microscope.