| Summary: | 碩士 === 國立海洋大學 === 水產食品科學研究所 === 83 ===
Three selective media, OA (Oxoid Aeromonas agar), BA (Blood ampicillin agar)and SA (Starch ampicillin agar) were used to evaluate the contamination of A. hydrophila in 66 samples includng oyster, shrimp, fish and surimi products. Oyster had the highest incidence, with 50% positive, while no A. hydrophilawas found in surimi products. In comparison with the detective rate of A. hydrophilafrom seafood among the three selective media, BA displayed the highest detective rate and OA had the least. The results from the analysis of the sterile seafood spiked with various amounts of A. hydrophila also demonstrated that the recovery rate of OA was significantly lowered than that of BA or SA; whereas the recovery rates between BA and SA were not significantly different. Fortyeight isolates from this survey were tested for their capability to produce hemolysin and cytotoxin. Hemolysin was produced by 79.2% of the isolates and cytotoxin was produced by 91.7% of the isolates in brain heart infusion broth. One of the toxin-producing isolate from oyster, strain 8169, was further tested for its proliferation and toxin production in oyster, shrimp or fish at various temperature. The results indicated that it grew best and had highest toxin productions in oyster. Hemolysin and cytotoxin were produced earlier at 28℃ than at 37℃, and titers of these toxins were also higher at 28℃ in oyster. Refrigeration (5℃) could retard cell growth and prevent cytotoxin production in oyster or shrimp. Moreover, it had highest toxin productions in aerobic condition with 120 rpm shaking, while had highest toxin productions in aerobic standing condition. Finally, the growth of forth-eight isolates in BHI broth with rarious pH values or salt levels at various temperature was investigated. The optimal growth temperature for all of the isolates was 28℃. All of them could grow at 45℃, although some of them (8.3%) grew slowly. Most of them (93.8%) could grow at 5℃, which demonstrated that they were psychrotrophs. A. hydrophilaisolates grew better in slightly basic mediu, especially at pH 8.5 at 28℃, most isolates could tolerate 4% NaCl solution, while at 5℃ 62.5% of isolates grew in 3% NaCl solution. In addition, all of th isolates could utilize L-arabinose, D-fructose, D-galactose, D-glucose, glycogen, maltose, D-mannose, salicin and sucrose, and none of them could use adonitol. The capability of the individual isolate for growing at various environmental conditions tested and the profiles of its sugar utilization did not correlate well with its toxin productivity.
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