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BAM: Vibrio
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May 2004

Bacteriological Analytical Manual
Chapter 9
Vibrio

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INTRODUCTION

Members of the genus Vibrio are defined as Gram-negative, asporogenous rods that are straight or have a single, rigid curve. They are motile; most have a single polar flagellum, when grown in liquid medium. Most produce oxidase and catalase, andferment glucose without producing gas (7). Three species, V. cholerae, V. parahaemolyticus, and V. vulnificus, are well-documented human pathogens (54,78,79, 90,101). V. mimicus (24,103,111), is a recognized pathogen (103) with similar characteristics to V. cholerae, except an ability to ferment sucrose. Other species within the genus, such as V. alginolyticus (51), V. fluvialis (71), V. furnissii(15), V. metschnikovii (39,70), and V. hollisae (40) are occasional human pathogens (1,39, 96). Vibrio species account for a significant proportion of human infections from the consumption of raw or undercooked shellfish (96). A Florida study of illnesses from raw shellfish consumption reported the following species in descending order of frequency; V. parahaemolyticus, non-O1/O139 V. cholerae, V.vulnificus, V. hollisae, V. fluvialis, O1 V. cholerae (64,72).
A number of substantial changes have been made in this version of the Vibrio chapter including greater emphasis on molecular methods such as DNA colony hybridization and PCR for identification and characterization of pathogenic Vibrio spp. With the addition of these options, less emphasis has been placed on some of the older methods andin some case some sections requiring dangerous or difficult to obtain reagents (i.e. O/129 reagent) have been eliminated but may be mentioned in the text or tables. There have been considerable advances in molecular detection techniques such as real time PCR and as these methods are validated, they will be incorporated into the web version of this chapter.

V. cholerae

V. cholerae (6), thetype species of the genus Vibrio, is the causative agent of cholera outbreaks and epidemics (34,54,126). Various biochemical properties and antigenic types characterize it. It can be differentiated from other Vibrio species, except V. mimicus, because its obligate requirement for sodium ion (Na+) (6) can be satisfied by the trace amounts present in most media constituents. Cholera enterotoxin (CT)is the primary virulence factor of the disease cholera. A genetic pathogenicity island designated VPI (vibrio pathogenicity island), which contains most genes necessary to cause cholera was demonstrated to regulate the CT gene (55). Most V. cholerae strains recovered from epidemic cholera cases contain a common somatic antigen and include serogroup O1 (54). Over 150 known somatic antigenic typeshave been identified. Strains that are agglutinable in Inaba or Ogawa serotypes of O1 antiserum are well-documented human pathogens. Until recently, only the O1 serogroup was associated with cholera epidemics. However, in 1993, a large outbreak of cholera occurred in India/Bangladesh from a new, until then unknown serogroup, O139 (3). Numerous cases were recorded in which patients had the typicalsymptoms of classical cholera, cholera gravis, previously only seen with the O1 serogroup. Except for the O antigen and the presence of a polysaccharide capsule, this serogroup is nearly identical to the seventh pandemic strain of V. cholerae (10). The O139 strain has become endemic in the Bengal region and is the cause of what may be known as the Eighth Cholera Pandemic (34,117).
V. choleraestrains that are identical to, or closely resemble, clinical strains in biochemical characteristics, but fail to agglutinate in either anti-O1 or -O139 sera are now referred to as V. cholerae non-O1/O139 (34,53,54). These serologically diverse strains are abundant in estuarine environments. Evidence indicates that non-O1/O139 strains are sporadically involved in cholera-like diarrheal disease...