The bacterial fiora on the skin and in the muscle of spoiled raw fish stored at 0.5°C was investigated.
Enumeration and isolation of bacteria was conducted with smear plate method using 1% NaCl containing agar or 50% sea water agar medium. Ten samples of fresh sea fish were used in this experiment. One hundred and four strains were isolated from the skin of the fresh fish, and 150 and 148 strains were isolated from skin and muscle of the spoiled fish, respectively. Among the total isolates Pseudomonas group III/IV was predominant, and Vibrio, Pseudomonas II and I, or Moraxella constituted a small percentage of them. The isolates classified as the above-mentioned Pseudomonas IIII/IV were found to be devided clearly into the two groups on the basis of the difference in the salt requirement. The halophilic group was tentatively designated as Pseudomonas III/IV-H, while non-halophilic one Pseudomonas III/IV-NH. The majority of the Moraxella and the Vibrio strains also showed slightly halophilic property. On the contrary, all of the Pseudomonas I and II strains were nonhalophiles. About 90% of the isolates from the skin of fresh fish consisted of the Pseudomonas III/IV-H, III/IV-NH, Vibrio and Moraxella. After spoilage, the Pseudomonas III/IV-H, III/IV-NH and the Vibrio also dominated in the flora both on the skin and in the muscle, and percentage of the Pseudomonas II and I strains increased to some extent instead of decrease in the Moraxella. The spoilage ability at 5°C of the pure cultures was tested organoleptically using yellow-tail muscle. Several of the Pseudomonas III/IV-NH and III/IV-H strains and some of the Vibrio produced typical offensive spoilage odour, while the other group strains showed only some atypical odours.