The spiral bacteria are spirilla (singular form is spirillum) and the rod-shaped bacteria are bacilli (singular form is bacillus). The coccus (plural form is cocci) bacteria are spherical and are usually found in clusters or chains.

Bacilli have a large surface area that helps them take in nutrients, but they may dry out easily. Cocci do not dry out as quickly and retain water, but they absorb nutrients slowly.

Spirilla have flagella at both ends, allowing them to move like a corkscrew, and they are capable of moving faster than other bacteria. Their rigid cell wall gives them their shape.

An example of cocci is Staphylococcus hominis, and it occurs commonly on human and animal skin harmlessly, but it may occasionally cause infection in patients with weak immune systems. An example of bacilli is Escherichia coli, and these live in the intestines of animals and decompose undigested food.

They are usually helpful or harmless, but some may cause food poisoning in their hosts. An example of spirilla is Leptospira interrogans, and these bacteria can cause leptospirosis, a disease that may lead to liver damage, but humans are accidental hosts and animals are most commonly infected.

Cite this article as: William Anderson (Schoolworkhelper Editorial Team), "Bacteria: Bacilli, Spirilla and Cocci," in SchoolWorkHelper, 2019,

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Grace Richter
Grace Richter
2 months ago

Hi – Wanted to point out a minor correction for the first sentence. The singular counterpart of “spirilla” is “spirillum”, not “spirillus”.

rami khalid
rami khalid
4 months ago

are cocci and bacilli Heterotrophs or autotrophs ?

Last edited 4 months ago by rami khalid
4 years ago


6 years ago

I want to know can we take it in a pill or liquid to help clean are liver from toxins

Reply to  Diane
4 years ago