Shumway / Rodrick Shellfish Safety and Quality

1. Auflage 2009
ISBN: 978-1-84569-557-6
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 612 Seiten

Reihe: Woodhead Publishing Series in Food Science, Technology and Nutrition

Shellfish are a very popular and nutritious food source worldwide and their consumption has risen dramatically. Because of their unique nature as compared to beef and poultry, shellfish have their own distinct aspects of harvest, processing and handling. Edited by leading authorities in the field, this collection of review papers discusses issues of current interest and outlines steps that can be taken by the shellfish industry to improve shellfish safety and eating quality.Opening chapters provide an overview of the key issues associated with microbial and biotoxin contamination. Parts two and three then address in more detail methods to improve molluscan shellfish and crustacean quality and safety. Chapters focus on detection of algal toxins, monitoring and mitigation of the effects of harmful algal blooms, metals and organic contaminants, biofouling, disease control and selective breeding. Part four reviews legislation, regulation, public confidence in shellfish and risk management. Chapters on post-harvest issues, such as depuration, storage and packaging complete the volume.With its distinguished editors and international team of experts, Shellfish safety and quality is an essential reference for those in the shellfish industry, managers, policymakers and academics in the field. - Reviews the latest research on significant hazards such as microbial and biotoxin contamination - Discusses effective management of shellfish safety and quality, including emerging methods - Examines improved packaging methods

Autoren/Hrsg.

Shumway, Sandra E.

Rodrick, Gary E

Leseproben

1 Microbial contamination and shellfish safety
S. Jones    University of New Hampshire, USA Abstract
Microbial contamination is a challenging and significant issue for the shellfish industry. It is the main public health concern associated with consuming shellfish, and it often limits shellfish harvesting throughout the world. Enteric viruses, pathogenic Vibrio species, and fecal-borne bacterial pathogens are the main causes of shellfish-borne disease. These microorganisms have widely different properties, sources, virulence factors, and fate in the environment, and the current indicators used to classify harvest waters have significant limitations. A great deal of progress is currently being made in the detection of pathogenic microorganisms and in understanding their fate in the environment. With increasing human development in coastal areas, emerging diseases, habitat destruction, and global climate changes, the challenges associated with managing microbial contamination and shellfish safety continues to evolve. Key words microbial contamination shellfish safety enteric viruses vibrios harvest water classification fecal pollution indicators microbial survival pollution sources 1.1 Introduction
The quality of coastal and estuarine waters throughout the world has become adversely impacted by a variety of contaminants, including microorganisms. In many areas where sewage treatment is inadequate, microbial contamination is by far the most important contaminant affecting shellfish safety. Even in well-developed areas, however, microbial contamination from nonpoint pollution remains a critical problem. The studies and results presented here reflect published findings that pertain to the study-specific geographical areas. Different findings and phenomena could be expected in other areas of the world because of differences, however, in environmental conditions and pollution characteristics. The main themes in this chapter include an initial definition of microbial contaminants and a discussion of those that are the major contaminants in shellfish. Human diseases are then presented to emphasize their significance to the shellfish industry and consuming public. Specific impacts of microbial contamination on the shellfish industry are then discussed, followed by an overview of their incidence in the natural environment and their sources. The final sections include probable future issues and trends in research, and a summary of useful sources for further information. 1.2 Major microbial contaminants of shellfish
Microbial contaminants as defined here are pathogenic microorganisms that cause disease in shellfish-consuming humans. Included are fecal-borne viral, bacterial and protozoan pathogens, and naturally occurring bacterial pathogens, but biotoxin-producing algae are excluded as they are covered in other chapters. It is also necessary to include fecal indicator and organisms used in microbial source tracking (MST). The indicator bacteria used within the shellfish industry are generally fecal (and total) coliforms and Escherichia coli. Enterococci, Clostridium perfringens and other indicators are also useful in helping to elucidate the sources and fate of fecal-borne contamination in shellfish waters (Watkins and Burkhardt, 1996). MST methods have effectively used other organisms such as Bacteroides spp. (Field et al., 2003), Bifidobacterium spp. (Bernhard and Field, 2000) and F-RNA coliphage (Vinje et al., 2004), among others, to track sources of fecal contamination. Though indicator organisms are not necessarily pathogens, their universal use for assessing shellfish safety necessitates their inclusion in this chapter. It is also useful to note that many new pathogen detection methods do not require culturing the target organism and focus instead on the direct detection of species, strain or virulence-specific genes from environmental samples. The issue of microbial contamination and shellfish safety can thus be addressed using methods that involve detection of microbial cells, genetic material, or both. The most frequent causes of shellfish-borne disease (CDC, 2006; Cato, 1998; Rippey, 1994) are of greatest concern. Most shellfish-borne diseases are likely caused by enteric viruses, though pathogenic vibrios are emerging as an increasing threat, and infections from Vibrio vulnificus have the highest fatality rate of any foodborne infectious agent. Fecal-borne bacterial pathogens have become less prevalent worldwide (Rippey, 1994) as a result of successes with their management, though they still account for a significant fraction of shellfish-borne disease in some areas (Cato, 1998). Thus, the major microbial contaminants include viruses, vibrios, and to a lesser extent fecal-borne bacteria. 1.2.1 Human pathogenic viruses
Viruses are species-specific intracellular parasites and are the leading cause of shellfish-borne disease in humans. Although human pathogenic viruses are readily taken up and accumulated, they do not infect or grow in molluscan shellfish. They can persist for extensive periods in the marine environment (Gantzer et al., 1998; Callahan et al., 1995) and in shellfish (Formiga-Cruz et al., 2002; Lees, 2000). The main source of human viruses is sewage from septic systems, wastewater treatment facilities and direct discharges, all human sources. Relatively high viral concentrations can exist in wastewater treatment facilities (Katayama et al., 2008; Gantzer et al., 1998), and standard treatments such as chlorination are only partially effective in inactivating or removing viruses from effluent (Tree et al., 2003; Tyrrell et al., 1995). Thus, varying yet potentially significant loading of viruses is discharged to shellfish harvest waters. Levels of viruses vary considerably over predictable cycles, with highest levels observed in winter months (Katayama et al., 2008; Formiga-Cruz et al., 2002; Burkhardt et al., 2000; Dore et al., 2000). This seasonal variation in environmental incidence relates well with the incidence of viral infections in humans, and is also influenced by environmental factors and the presence of individuals carrying pathogenic viruses within the human population. Lees (2000) summarized the many common types of human viruses that have been associated with contaminated shellfish, including the rotaviruses, astroviruses, enteroviruses, adenoviruses, hepatitis A, and the calciviruses. Small round structure viruses are a subset of calciviruses that include Norwalk-like viruses (NLV). Viruses most commonly associated with infectious disease incidents through shellfish consumption are NLV and hepatitis A, though they produce different disease symptoms. Viruses are comparatively more difficult to remove from shellfish than most bacteria (Schwab et al., 1998). In addition, considerable effort has therefore been focused on their detection in shellfish because they are also more difficult to detect (Myrmel et al., 2004; Le Guyader et al., 2003; Lees, 2000; Green et al., 1998; Henshilwood et al., 1998; Dore and Lees, 1995). 1.2.2 Pathogenic vibrios
The genus Vibrio is comprised of bacteria found free-living in marine environments and at elevated levels in association with a variety of eukaryotic hosts, including shellfish (Thompson et al., 2004) and seaweeds (Mahmud et al., 2007). They play key roles in ecosystem carbon cycling, as an important food source for copepods and as light organ symbionts. In other cases vibrios are pathogens, primarily of shellfish and fish, though the human pathogens are notable. Of particular concern are Vibrio cholerae (Colwell, 2004), Vibrio vulnificus (Gulig et al., 2005; Linkous and Oliver, 1999) and Vibrio parahaemolyticus (Yeung and Boor, 2004), which cause severe diarrheal disease, gastroenteritis, wound infections, and septicemia (Thompson et al., 2004). Their normal association with shellfish presents a common mechanism for human infection (Morris, 2003; Potasman et al., 2002). V. hollisae and other potentially pathogenic species are of less concern at present. The widespread and consistent detection of V. vulnificus and V. parahaemolyticus in bivalve shellfish suggests shellfish as an important ecological niche for these vibrios. Persistence appears to involve interactions between the vibrios and the shellfish hemolymph that result in low levels of elimination (Pruzzo et al., 2005). The presence of a protozoan pathogen of oysters, Perkinsus marinus, can lead to greater inefficiency of oyster hemolymph for eliminating V. vulnificus (Tall et al., 1999). Levels in oysters may also depend on oyster genotype (Sokolova et al., 2006). The lack of elimination of V. vulnificus may lead to significant growth that may be shed to overlying waters (Tamplin and...