腸炎ピブリオ(Vibrio parahaemolyticus)における白糖分解能の判定結果に及ぼす2, 3の因子について
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On the course of examination of sucrose-fermentability of Vibrio parahaemolyticus isolated from the stool of food poisoned patients, it was recognized that the sucrose-negative strains gave the intermediate appearance between positive and negative, or positive appearance in some case, with No.15 liquid medium (confirmation medium) or Artificial Marine Water medium, though they gave clearly negative on TCBS agar plates (isolation medium) or with the Simmons medium. The causative agents to decrease the pH of the medium were metals such as Cu++, Pb++ and Sn++ which were contaminated in the distilled water used. These metal ions catalyze the hydrolysis of sucrose to glucose and fructose during autoclaving at 120C for 20min. Acids which were produced from those reduced sugars by sucrose-negative strains decreased the pH of the weakly buffered AMW medium, but not of strongly buffered Simmons medium. However, the amounts of the acids produced by sucrose positive strains from sucrose was large enough to decrease the pH of both AMW and Simmons media.This conclusion came from the following observation: 1) The distilled water which gave the paradoxical results contained 0.25μg/ml of cupper ions as expected. 2) The medium made with deionized water did not give such a funny results. 3) If CuSO4 was added to the sucrose solution before autoclaving at a final concentration of 1.0μg/ml, 2∼3% of sucrose was converted to the reducing sugars. The false positive results on the sucrose-fermentability was always found by the above sucrose solution. 4) When the sucrose, sterilized by membrane filter, was used, the pH changing curve was the identical with that without sucrose. If glucose, instead of sucrose, was added into such media, the extents of the decrease in pH were proportional to the amount of glucose added and independent of the amounts of sucrose. 5) When the medium was autoclaved in the presence of CuSO4, the extent of the decrease in pH was also proportional to the amounts of reduced sugars produced from sucrose by autoclaving. 6) The buffering ability of Simmons medium was much stronger than AMW medium.Thus, the sucrose fermentability can be determined accurately if one used the pure water which does not contain metal ions and a strong buffered medium as Simmons.