Bacteria

bacteria. (beak-ti'-ree-uh)

    A group of unicellular microorganisms that lack chlorophyll and reproduce rapidly by simple fission. They are classed according to their shape or on the basis of their oxygen requirements. Bacilli (singular: bacillus) are rod shaped; cocci (singular: coccus) are spherical or ovoid; vibro are comma shaped; and spirillum are curved and rodlike. Aerobic bacteria require atmospheric oxygen whereas anaerobic bacteria cannot live in the presence of oxygen. Bacteria develop under strict conditions of pH, temperature, and humidity (above 90 percent) and may be killed by disinfectants. They are responsible for certain diseases and for the degradation and spoilage of food.