ABSTRACT
Vibrios are short curved or straight cells, single or united into spirals that grow well and rapidly on the surfaces of standard culture media and can be readily isolated from estuarine, marine, and fresh water samples. These heterotrophic organisms vary in their nutritional requirements; some occur as parasites and pathogens for animals and for man. The short curved, asporogenous, gram-negative rods that are members of the genus Vibrio are most commonly encountered in the estuarine, marine, or fresh water habitat. Distinguishing species of the genus Vibrio from other related genera can be presumptively accomplished by examining Gram stains of carefully prepared specimens, followed by electron microscopy to conrm morphology. In contrast, Spirillum isolates are frequently seen as rigid, helical cells with a single or several turns, motile by means of bipolar polytrichous agella, whereas Vibrio species are short rods with a curved axis, motile by means of a single polar agellum. However, Vibrio species may be short, straight rods (1.5-3.0 μm × 0.5 μm), or they may be S shaped or spiral shaped when individual cells are joined. Possession of two or more agella in a polar tuft has also been demonstrated in Vibrio species, as have lateral agella, notably Vibrio parahaemolyticus. Thus, to identify and classify vibrios, physiological and biochemical taxonomic tests are made.1 Vibrio species are facultatively anaerobic, with both a respiratory (oxygen-utilizing) and a fermentative metabolism. Related genera may be aerobic or microaerophilic, with a strictly respiratory metabolism (oxygen is the terminal electron acceptor). Early on, Hylemon et al.2 proposed a division of the genus Spirillum into three genera-Spirillum, Aquaspirillum, and Oceanospirillum; supported by the work of Carney et al.,3 results based on molecular genetic studies have seen the reduction of Spirillum spp. to single species, that is, Spirillum volutans, with other species moved to other genera. Vibrios require 1%–3% NaCl for growth and the salt requirement is absolute.
