283
It is reported that 20% of all outbreaks of shellfish include Vibrio species, while
Salnonella, Shigella and Listeria species are other species (Potasman et al. 2002).
5.2.1.1 Vibrio Species
Various species of Vibrio, specific to both marine and river mouth environments
have been identified as factors of human diseases associated with shellfish. These
include Vibrio parahaemolyticus, Vibrio vulnificus, Vibrio cholerae, Vibrio fluvialis,
Vibrio hollisae, Vibrio mimicus, Vibrio alginolyticus and unidentified or various
Vibrio species (Hariharan and Amadi 2016). Vibrios are among the fastest growing
bacteria in nature. If they are not cooled immediately after harvest, they easily grow
in molluscan shellfish. Vibrio cholerae, Vibrio vulnificus and Vibrio parahaemolyticus are the most important pathogens. The pathogens, V. vulnificus and V. parahaemolyticus, can cause waterborne diseases, but are particularly dangerous when
combined with a filter-feeding vector, such as molluscan shellfish. Filter-feeding
molluscs pump the surrounding water over their gills, simultaneously obtaining
oxygen and food. Vibrio spp. are often found attached to particles and as these particulates are passed over the sieve-like gills of filter-feeding molluscs, they are
strained out of the water and retained (Raszl et al. 2016).
It has been reported that in naturally contaminated bivalve molluscs, vibrios cannot be easily removed by depuration (Vasconcelos and Lee 1972; Rodrick and
Schneider 1991; Wright et al. 2009) compared to faecal bacterial indicators such as
E. Coli (Lee and Rangdale 2008). It has been reported that artificial depuration is
not reliable to eliminate Vibrio parahaemolyticus in oysters (Croci et al. 2005), and
even depuration may cause cross contamination of V. parahaemolyticus in other
oysters (Ramos et al. 2012).Therefore, such processing methods may not be sufficient to maintain the necessary public health in the harvested product contaminated
with vibrios (Lee and Rangdale 2008). Eyles and Davey (1984) also reported that
depuration did not reduce V. parahaemolyticus levels in shellfish. It is reported that
another method of purification involving the transport of shellfish from a limited
harvesting area to an open area where natural cleaning can occur is available, but it
will not be relied upon to completely eliminate V. vulnificus in shellfish (Drake
et al. 2007).
All vibrios are heat sensitive. It is reported that in the heat treatment applied to
shellfish, a heating that will increase the internal temperature to 60 °C will be sufficient to eliminate pathogenic vibrios, and chilling and refrigeration are critical
control measures to prevent the growth of these microorganisms (Dalsgaard et al.
2001). It is reported that V. vulnificus is known to grow between 8–43 °C and
V. parahaemolyticus grows within the 5–45.3 °C range (Baker 2016).
The heat shock process applied for shucking the oysters was determined to
reduce the level of V. vulnificus in oyster meats. Additional reductions were found
immediately after the heat shock during the washing and cooling phases (Hesselman
et al. 1999). Heating oysters for 10 min at 50 °C in water was determined to be sufficient to reduce V. vulnificus to an undetectable level (Cook and Ruple 1992). It has
5.2 Microbial Risks
It is reported that 20% of all outbreaks of shellfish include Vibrio species, while
Salnonella, Shigella and Listeria species are other species (Potasman et al. 2002).
5.2.1.1 Vibrio Species
Various species of Vibrio, specific to both marine and river mouth environments
have been identified as factors of human diseases associated with shellfish. These
include Vibrio parahaemolyticus, Vibrio vulnificus, Vibrio cholerae, Vibrio fluvialis,
Vibrio hollisae, Vibrio mimicus, Vibrio alginolyticus and unidentified or various
Vibrio species (Hariharan and Amadi 2016). Vibrios are among the fastest growing
bacteria in nature. If they are not cooled immediately after harvest, they easily grow
in molluscan shellfish. Vibrio cholerae, Vibrio vulnificus and Vibrio parahaemolyticus are the most important pathogens. The pathogens, V. vulnificus and V. parahaemolyticus, can cause waterborne diseases, but are particularly dangerous when
combined with a filter-feeding vector, such as molluscan shellfish. Filter-feeding
molluscs pump the surrounding water over their gills, simultaneously obtaining
oxygen and food. Vibrio spp. are often found attached to particles and as these particulates are passed over the sieve-like gills of filter-feeding molluscs, they are
strained out of the water and retained (Raszl et al. 2016).
It has been reported that in naturally contaminated bivalve molluscs, vibrios cannot be easily removed by depuration (Vasconcelos and Lee 1972; Rodrick and
Schneider 1991; Wright et al. 2009) compared to faecal bacterial indicators such as
E. Coli (Lee and Rangdale 2008). It has been reported that artificial depuration is
not reliable to eliminate Vibrio parahaemolyticus in oysters (Croci et al. 2005), and
even depuration may cause cross contamination of V. parahaemolyticus in other
oysters (Ramos et al. 2012).Therefore, such processing methods may not be sufficient to maintain the necessary public health in the harvested product contaminated
with vibrios (Lee and Rangdale 2008). Eyles and Davey (1984) also reported that
depuration did not reduce V. parahaemolyticus levels in shellfish. It is reported that
another method of purification involving the transport of shellfish from a limited
harvesting area to an open area where natural cleaning can occur is available, but it
will not be relied upon to completely eliminate V. vulnificus in shellfish (Drake
et al. 2007).
All vibrios are heat sensitive. It is reported that in the heat treatment applied to
shellfish, a heating that will increase the internal temperature to 60 °C will be sufficient to eliminate pathogenic vibrios, and chilling and refrigeration are critical
control measures to prevent the growth of these microorganisms (Dalsgaard et al.
2001). It is reported that V. vulnificus is known to grow between 8–43 °C and
V. parahaemolyticus grows within the 5–45.3 °C range (Baker 2016).
The heat shock process applied for shucking the oysters was determined to
reduce the level of V. vulnificus in oyster meats. Additional reductions were found
immediately after the heat shock during the washing and cooling phases (Hesselman
et al. 1999). Heating oysters for 10 min at 50 °C in water was determined to be sufficient to reduce V. vulnificus to an undetectable level (Cook and Ruple 1992). It has
5.2 Microbial Risks