Pathogenic vibrio species in the marine and estuarine environment

Abstract

The genus Vibrio includes more than 30 species, at least 12 of which are pathogenic to humans and/or have been associated with foodborne diseases (Chakraborty et al., 1997). Among these species, Vibrio cholerae, serogroups O1 and O139, are the most important, since they are associated with epidemic and pandemic diarrhea outbreaks in many parts of the world (Centers for Disease Control and Prevention, 1995; Kaper et al., 1995). However, other species of vibrios capable of causing diarrheal disease in humans have received greater attention in the last decade. These include Vibrio parahaemolyticus, a leading cause of foodborne disease outbreaks in Japan and Korea (Lee et al., 2001), Vibrio vulnificus, Vibrio alginolyticus, Vibrio damsela, Vibrio fluvialis, Vibrio furnissii, Vibrio hollisae, Vibrio metschnikovii, and Vibrio mimicus (Altekruse et al., 2000; Hø et al., 1997). In the USA, Vibrio species have been estimated to be the cause of about 8000 illnesses annually (Mead et al., 1999). Vibrios can be classified as either halophilic or nonhalophilic, depending on their requirement for NaCl for optimal growth (Thompson et al., 2004). They are free-living bacteria in the aquatic environment throughout the world. They tend to be more common in warmer waters, notably when temperatures rise above 17 °C and, depending on the species, they tolerate a wide range of salinities (Wright et al., 1996). Given their abundance in water, Vibrio species are also commonly isolated from fish and shellfish, with 100-fold higher concentration in filter-feeding shellfish, such as oysters, than in the surrounding water (Wright et al., 1996). During the warm summer months, virtually 100% of oysters can carry V. vulnificus and/or V. parahaemolyticus (Cook et al., 2002b; Motes et al., 1998; Wright et al., 1996). "Epidemic" strains of V. cholerae, which carry specific virulence genes, cause the disease "cholera," while "nonepidemic" strains are mainly associated with septicemia, gastroenteritis, and wound infections (Levine and Griffin, 1993). However, morbidity due to nonepidemic strains is relatively low, and, in some instances, it is unclear whether isolation of the organism represents asymptomatic colonization or infection. In fact, given the ubiquitousness of the genus in the environment, asymptomatic colonization may occur.