WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2015 61 L. monocytogenes. Coliforms were cultured in lactose broth and enumerated using the Most Probable Number (MPN) method. We used the m-ColiBlue24® filtration method to assay for E. coli and coliforms. Not surprisingly, bacterial detection in the macroalgae approximated the bacterial detection in culture waters. No V. parahaemoloyticus or L. monocytogenes were detected in either culture water or any macroalagal species, either at harvest or after seven days of cold storage. Also, E. coli was not detected in any macroalgal sample. This is encouraging because fresh seaweed is often not used immediately in restaurants or may be stored at a retailer before consumption. Total coliforms were detected by the MPN method in all macroalgae species for freshly harvested and stored samples, although the levels did not increase during storage. Detecting total coliforms was not unexpected, given that some of the incoming water came from fish rearing tanks and that the culture tanks were open to access by birds (Fig. 2). Although we detected no or low levels of known seafood pathogens, the culture conditions of our study may not be typical for larger-scale macroalgal aquaculture operations. For example, the culture water in this study was processed (filtered and ultraviolet light-treated) to remove most bacteria present in raw seawater before passing through fish culture tanks. Furthermore, the study was conducted during June and July only, which does not incorporate potential effects of temperature fluctuations, rainfall, and stormwater runoff on ambient bacterial abundances. Future Food Safety Needs for Cultured Macroalgae These preliminary results suggest that adaptation of shellfish seafood safety protocols from the BAM is a good starting point for developing methods to screen cultured macroalgae for bacterial pathogens. Whether methods in use for animal tissue or animal products could be applied to plant tissues with equivalent sensitivity requires assessments such as spiking samples with known titers of bacteria. Obviously protocol development requires methods that can be reliably replicated within and among laboratories and our efforts from a salmon broodstock facility. Rearing of macroalgae in landbased systems allows better control of growth conditions, product quality and minimizes user conflict issues common to extensive rearing in public waters. Bacteriological Testing of Cultured Macroalgae Many forms of macroalgae are consumed raw or after storage in brine. Bacteria such as Escherichia coli and Vibrio parahaemolyticus can cause illness after consuming raw seafood such as oysters, while the disease bacterium Listeria monocytogenes can grow in up to 10 percent salt, such as in cold-smoked fish. To ensure a wholesome and safe product, methods for testing seaweed for potentially harmful bacteria are needed. The Bacteriological Analytical Manual (BAM) is the U.S. Food and Drug Administration’s document of preferred methods for analyzing food and cosmetics for potentially harmful microorganisms. The BAM contains assays for detecting L. monocytogenes, V. parahaemolyticus, and E. coli in shellfish and other seafood, but not for macroalgae, for which we adapted existing BAM methods (Hitchins and Jinneman 2001, Feng et al. 2002, Kaysner and Depaola 2004). In addition to BAM methods for E. coli and total coliforms, we also tested a commercial kit approved by the U.S. Environmental Protection Agency (USEPA 2009) for testing water.1 Freshly harvested seaweed and seaweed stored for seven days at 4 C were tested. Culture water for testing was collected at three different locations in the culture system: bay water near the intake pumps, influent water at the tank and tank water adjacent to seaweed. Macroalgal tissue was homogenized to a slurry with a Waring blender and serial dilutions were prepared for culture with selective media for each of the three bacterial species of interest (Fig. 3). Water samples were prepared in the same way, but without homogenization. For V. parahaemolyticus, we prepared samples in alkaline peptone water and cultured on thiosulfate citrate bile sucrose agar, which changes from dark blue to yellow in the presence of acid production by bacteria, a common characteristic of Vibrio species (Fig. 3). For L. monocytogenes, we prepared and enriched samples in buffered Listeria enrichment broth and cultured on chromogenic Brilliance™ Listeria agar2, which changes from green to yellow with (CONTINUED ON PAGE 62) FIGURE 2. Land-based macroalgal culture system at Northwest Fisheries Science Center’s Manchester Research Station on Puget Sound, in Washington State. Left, overview of culture tanks; right, close-up of tanks. Photos: John Colt and Vanessa Carrasco.
RkJQdWJsaXNoZXIy MjExNDY=