Singular 'bacterium.' Microscopic single-cell (unicellular) life form that exists practically everywhere in the Earth's environment, and is simpler than the cells of animals, fungi, and plants. Of about three million species of bacteria believed to exist, only about 4,000 are known and are divided into five general groups according to their shape: bacilli (rod shaped), cocci (ball shaped), filamentous (thread like), spirilla or spirochetes (spiral shaped), and vibrio (comma shaped). Some are free-living, harmless or beneficial (even essential) to other life forms, others are parasitic and produce toxins that cause disease or death.

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  • While most people consider bacteria to be a nasty germ that must be destroyed at all cost, there are in fact some good bacteria in the world that is necessary for the body to function properly.

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  • My doctor always washes his hands and uses new gloves before he operates so he can make sure that bacteria doesn't infect an open wound on a patient.

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  • She was worried about bacteria growing on her counter, so she used a bleach disinfectant to wipe down the entire length.

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