Spirillum(redirected from spirilla)
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a bacterium having the shape of a spirally twisted or arched rod. Depending on the species, spirilla range in width from 0.6 to 3 microns and in length from 1 to 50 microns. Spirilla do not form spores and are gram-positive. They are motile, owing to the presence of a bundle of flagella at the end of the cell. Some species grow poorly on laboratory nutrient mediums; a number of species have never been isolated in pure culture. Spirilla are saprophytes. They inhabit fresh and salt waters, as well as putrefying stagnant water, liquid manure, and the contents of animal intestines.