Abstract
This study characterized microbiological and chemical contamination of oyster meat and estuarine water in Phang Nga, Thailand. Pooled oyster meats (n = 144), estuarine waters (n = 96) and environmental parameters were collected from March, 2016 to February, 2017, and assessed for levels of total coliforms (TC), fecal coliforms (FC), Escherichia coli (EC), and Vibrio parahaemolyticus (VP), presence of Salmonella and Shigella and levels of heavy metals (Mn, Pb and Cd). The prevalence of TC, FC and EC were in 99.3%, 94.4% and 93.1% of oyster meat and 94.8%, 79.2%, and 78.1% of water, respectively. The average VP levels was 8.5 × 107 most probable number (MPN)/g oyster. Prevalence of Shigella and Salmonella in the pooled oysters were 7.6% and 30.6%, respectively. The dominant Salmonella serovars were Paratyphi B followed by Seremban, and Kentucky. In contrast, the prevalence of Shigella were 27.1%, but Salmonella was not detected in estuarine water. Factors statistically associated with EC accumulation in oyster were level of FC, 7-day average precipitation, temperature, relative humidity, and presence of Salmonella in the sample. The optimal cutoff value of EC to predict Salmonella in oyster was 420 MPN/g. Results indicate this area has relatively safe levels of heavy metals, whereas bacterial contamination was very high for oysters.
Highlights
Shellfish products have been recognized as relatively inexpensive and nutritious sources of protein, minerals and vitamins, and there is growing global demand for shellfish products given the wide recognition of their nutritional value [1]
The novelty of this study is to explore potential contributing factors that could be used to quantify the number of bacterial contaminations of oyster meat and estuarine water, and to estimate an optimal cut-off value of Escherichia coli (EC) contamination to predict
These results indicate that once the concentration of EC was greater than 420 most probable number (MPN)/g oyster meat, there was a high probability of Salmonella contamination in oyster meat in southern Thailand
Summary
Shellfish products have been recognized as relatively inexpensive and nutritious sources of protein, minerals and vitamins, and there is growing global demand for shellfish products given the wide recognition of their nutritional value [1]. Global fisheries and aquaculture production was 158 million tons (MT) in 2012, of which aquatic animal capture was 91.3 MT compared to 66.6 MT from aquaculture. The export of fish and fishery products from Thailand has been ranked among the top. In Thailand, bivalve production was estimated at 210,000 tons in 2014 [2], with most of these seafood products consumed domestically due to the high consumer demand in the country. Despite this high domestic demand, aquaculture production of shellfish such as oysters is at risk from human activities like environmental pollution. Development of an aquaculture industry for oysters in Phang Nga Bay has benefited from a plentiful supply of natural oyster larvae, no excessive influx of fresh water, intact shorelines and an enclosed and protected
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