Growth of Klebsiella Pneumoniae Uh-2 and Properties of Its Histidine Decarboxylase System in Resting Cells

Klebsiella pneumoniae UH-2, previously isolated from spoiled skipjack tuna grew rapidly at 37C, 25C and 10C (generation times of 0.64, 0.79 and 4.57 h, respectively) and produced large amounts of histamine at these temperatures. Histamine was found during storage of resting cells at 2C, but growth did not occur. The K. pneumoniae UH-2 histidine decarboxylase system has in situ properties that may contribute to rapid histamine formation in fish tissue. The conversion of histidine to histamine in situ had an apparent Km = 0.98 mM at the optimum pH, 4.0, with ca. 70% of this activity at pH 6. These properties and recent reports of its prominence in fish spoilage suggest that K. pneumoniae could play a major role in the formation of histamine in susceptible species.