Prevalence of Clostridium botulinum in Seafood and Significance of Multiple Incubation Temperatures for Determination of Its Presence and Type in Fresh Retail Fish

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Abstract
Two surveys for the presence and type of Clostridium botulinum in fresh seafood obtained from local supermarkets, processors, a fish farm, and a state hatchery were conducted between 1984 and 1987. During the first survey, we analyzed 166 samples representing 14 types of fish and 5 other types of seafood. An overall prevalence of 21.7% was found. Thirty-three samples (19.9%) harbored C. botulinum type A, 4 (2.4%) type B, 1 (0.6%) type E, and 1 sample (0.6%) type F. The most probable number (MPN) for C. botulinum in Pacific rockfish (red snapper) and salmon ranged from 9–240 and 3–120 organisms/100 g, respectively, in selected samples. The second survey examined 54 samples of fresh fillets representing 15 types of fish. Seventy grams of homogenate were vacuum packaged and incubated at 30°C for 3 d. Of the 54 samples, 36 (66.7%) resulted in toxin production. Of these 36 samples, 18 had type A C. botulinum, 8 type E, 4 nonproteolytic (np) type B, 2 proteolytic type B, 1 type F (np), and 3 harbored both type A and E organisms. When duplicate samples of each homogenate were incubated at 12°C for 8 d and at 8°C for 14 and 28 d, seven more samples initially shown at 30°C to harbor only one type of C. botulinum revealed the presence of a second type (4 had type E and 3 had B [np]). The high prevalence of nonproteolytic spore types is of particular significance when considering the risk of C. botulinum growth in fresh and minimally processed seafood stored for extended times under modified atmospheres at low temperatures.