prevalence and molecular characteristics of vibrio species in pre ...

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(2008) analyzed the genetic relatedness and geographical distribution of V.
parahaemolyticus from the environment and clinical strains using seven house
keeping genes (dnE, gyrB, recA, dtdA, pntA, pyrC, tnaA).
2.7.5 Molecular and genetic characteristics of environmental Vibrio
Vibrio species are widely distributed in the aquatic environment and are
considered as autochthonous bacteria in the estuarine and marine waters (Nishibuchi
and Kaper, 1995). Scientists isolated and identified this organism in the marine water
(Faruque et al., 2004, Nair et al., 1988), shrimp and oysters (Dalsgaard et al., 1995 a,
Gopal et al., 2005, Sobrinho et al., 2010), sediments (Bhaskar and Setty, 1994),
plankton (Lipp and Rose, 1997), and also from the seafood (Chitov et al., 2009 b,
Sujeewa et al., 2009). Many investigations were carried out to identify genetic and
phenotypic differences between clinical and environmental vibrios.
V. cholerae serogroups O1 and O139 caused the epidemics of cholera. But
other non O1 and non O139 serogroups can cause sporadic diarrhoea. Environmental
strains mainly belong to V. cholerae serogroup non O1 and non O 139 (Faruque et al.,
2004). Clinical strains carry the virulence factors for cholera toxin (CT) and toxin-
coregulated pilus (TCP) which is central to the disease process and provide adhesion
for the toxins respectively (Chakraborty et al., 2000). Studies found that
environmental strains of V. cholerae rarely carried CT and TCP. Water samples from
two major rivers of Bangladesh were investigated for the presence of V. cholerae and
their virulence associated genes. V. cholerae non O1 and non O139 was found in
89.9% (116/125) and 3.2% (4/125) were V. cholerae O1 (Faruque et al., 2004). These
authors found one V. cholerae O1 carrying the TCP and CT gene (0.8%) in those
environmental samples. Nair et al. (1988) carried out an investigation on V. cholerae
non O1 from environmental sources in India, to describe toxin profile. They examined
for the production of CT, shiga-like toxin (vero toxin), heat stable enterotoxin and
haemolysins. Two of the strains (0.5%) produced CT; none of them produced shiga-
like toxin or heat stable enterotoxins. Haemolytic activity was observed in 89.7% of
the strains. The authors concluded that only a small percentage of environmental V.
cholerae non O1 has the ability of causing cholera like symptoms (Nair et al., 1988).