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What is a Bacterium?

An introduction to a Bacterium.

Advanced Vaccine Research Methods for the Decade of Vaccines
Edited by: Fabio Bagnoli and Rino Rappuoli
A thorough and up-to-date review of vaccinology research in age of ‘omics’ technologies. Essential reading for everyone working in vaccine R and D.
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A Bacterium

A bacterium is the singular form of the plural word "bacteria". To put it another way, you use "bacterium" when there is only one of them and only use the word "bacteria" if you are refering to more than one. Many people get this wrong and you often see a phrase such as "a bacteria can cause disease" when of course it should be "a bacterium can cause disease".

A bacterium is a living cell consisting of a fluid called cytoplasm enclosed by a cell membrane and cell wall. A bacterium contains DNA in the cytoplasm in the form of a chromosome. Although a bacterium only has one chromosome it can have other, smaller DNA elements called plasmids. The chromosome of a bacterium is never surrounded by a nuclear membrane and this fact defines a bacterium as a prokaryote. Organisms that have their DNA in a nucleus surrounded by a nuclear membrane are called eukaryotes. A bacterium also has ribosomes in the cytoplasm. Ribosomes are involved in making proteins.

Many people confuse a bacterium and a virus. They are totally different in many ways. A bacterium is much bigger than a virus. A bacterium is much more complex. One very important difference is that a bacterium can be killed with an antibiotic while a virus cannot. So if you have a viral infection antibiotics will not help. However, antibiotics are sometimes used to prevent people with a virus infection from catching another (bacterial) infection.

Viruses and bacteria are both microorganisms. The study of bacteria is called bacteriology and it is a branch of microbiology.

Recommended reading at Bacteriology books and current topics on microbiology research at the Microbiology Blog