Bacteria are microscopic cells that are prokaryotic in structure. The term prokaryotic means their DNA (deoxyribosenucleic acid) is distributed throughout the entire cytoplasm of their cell interior. There is no nucleus, neither are any of the other membrane-covered organelles that are present in eukaryotic cells. The only organelle bacteria have are ribosomes, used in protein manufacture.
Bacteria come in three different growth patterns, or shapes. There are round, spherical shapes that are called cocci, or coccus. There are bacteria that possess a rod-like shape, and they are called bacilli, or bacillus. Finally, there are bacteria that resemble a spiral shape, and they are called spirilla, or spirillus.
Not all bacteria are harmful; some are necessary for food and beverage production. There are bacteria that are common to the digestive system that help us digest our food. Harmful bacteria can be treated with medicines called antibiotics, which kill the bacteria without harming existing cells in the body.