Spoilage in skipjack tuna (Katsuwonus pelamis) was studied under controlled conditions by incubating whole, fresh fish in seawater at 38°C, the optimum temperature for histamine formation. Bacterial isolates were obtained from the loin tissue of a decomposing tuna containing 134 mg of histamine per 100 g and a total anaerobic count of 3.5 x 105/g after incubation for 24 h. Over 92% of the 134 isolates obtained were facultatively or obligately anaerobic bacteria. Eighteen isolates produced histamine in culture media containing histidine, and these were identified as Clostridium perfringens, Enterobacter aerogenes, Klebsiella pneumoniae, Proteus mirabilis, and Vibrio alginolyticus. Histidine decarboxylase activity of several isolates was measured in a tuna broth medium and with resting cells suspended in a buffered histidine solution.

The three concentric layers of the cell wall of E. coli B (the outer lipoprotein layer, the intermediate lipopolysaccharide layer and the inner protein- and mucopolymer containing rigid layer) contribute 60%, 12% and 21%, respectively, to the total weight of the cell wall. — Treatment of the rigid layer with proteolytic enzymes removes the bulk of its protein components but leaves it otherwise intact: still rigid and cell-shaped, it is found to contain glucose, lipid and the mucopeptide constituents muramic acid, glucosamine, diaminopimelic acid, glutamic acid and alanine in molar ratios corresponding to the chemical compositions of known enzymatic mucopolymer split-products from E. coli-walls. Quantitative balance sheets of these components are made up and their implications on the structural concept of the rigid layer are discussed.

Elion (1924) was the first to isolate a thermophilic sulfate reducing bacterium in pure culture. He named the organism Vibrio thermodesulfuricans, and reported that it was capable of sulfate reduction betveen 30 and 65 C, wvith an optimum of 55 C. Baars (1930) and Kluyver and Baars (1932) reisolated V. thermodesulfuricans, and carried out a comparative study of this organism and Vibrio desulfuricans. They reported that it was possible to adapt cultures of V. desulfuricans, initially capable of growth only at 30 C, to grow up to 55 C by gradually increasing the incubation temperature. The reverse phenomenon was also demonstrated with V. thermodesulfuricans. They concluded that V. thermodesulfuricans should be regarded as a temperature adapted strain of V. desulfuricans. The sulfate reducing bacteria are now placed in the genus Desulfovibrio, created by Kluyver and Van Niel (1936). Starkey (1938) isolated cultures from sewage, mud, and soil at 30 and 55 C. Contrary to the findings of earlier investigators, all of the cultures isolated at 55 C were large, slightlv curved,

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Decomposition and histamine formation were studied with fresh mahimahi (Coryphaena hippurus) incubated in seawater at 0, 10, 21, and 32°C. The rates of decomposition (loss of quality) and histamine formation both increased at warmer incubation temperatures. Spoilage bacteria were primarily psychrotrophic at 0 and 10°C, while mesophilic bacteria predominated at 21 and 32°C. An increase in pH of the loin tissue was correlated slightly with the histamine level. The correlation between histamine level and loss of quality, however, was high. Also there was a strong correlation between odor of the fillet and histamine production during spoilage. Prior frozen storage at −20°C inhibited the rate of subsequent histamine formation, but did not affect the extent of quality loss. Loss of histamine during cooking (baking or steaming) had no appreciable effect on the residual histamine level of spoiled fish. Seawater was a much more efficient heat transfer medium than air during incubation. The rates of histamine formation and loss of quality were significantly greater in seawater than in air at the same temperature.