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A family of usually motile, aerobic to facultatively anaerobic bacteria (order Pseudomonadales) containing gram-negative, rod-shaped cells that are curved or spirally twisted. Motile cells contain a single polar flagellum or a tuft of polar flagella. These organisms are primarily water forms, although some are parasitic or pathogenic on humans and other higher animals. The type genus is Spirillum. See: Spirillum.