HiMedia – M1832_HiCrome™ Coliform Agar Modified

Principle and Interpretation
HiCrome™ Coliform Agar Modified is a selective medium recommended for the simultaneous detection of E.coli and thermotolerant coliforms in water and food samples (4). Peptone special and yeast extract provide the neccssary nitrogen compound, carbon, vitamins and also some trace ingredients required for the growth of organisms. The phosphates buffer the medium well. Magnesium sulphate helps colour development. Bile salts inhibits gram-positive organisms. Sodium chloride maintains osmotic balance. The chromogenic mixture contains two chromogenic substrates, which enables the detection of two specific enzymes, b-galactosidase and b-glucoronidase. b-galactosidase produced by coliforms cleaves one chromogen, resulting in the pink colouration of coliform colonies. The enzyme b-glucuronidase produced by E. coli, cleaves X-glucuronide. E.coli forms dark blue to violet coloured colonies due to cleavage of both the chromogens (1, 2, 3). E.coli strains that are b-glucoronidase negative (serotype O157:H7) produce pink coloured colonies. Other gram negative bacteria able to grow at (44±0.5)°C produce white or colourless colonies. Transfer 1 ml of product to analyse and its tenfold dilutions to sterile Petri plates. Pour 12 ml of medium, mix well and allow to solidify. Overlay with 4 ml of medium, allow to solidify and incubate at 43-45°C for 18-24 hours.

原理與解釋
HiCrome™Coliform Agar Modified是一種選擇性培養基，推薦用於同時檢測水和食物樣品中的大腸桿菌和耐熱大腸桿菌（4）。蛋白腖特殊酵母提取物提供了必需的氮化合物，碳，維生素以及生物生長所需的一些微量成分。磷酸鹽緩衝介質。硫酸鎂有助於顏色的發展。膽汁鹽抑制革蘭氏陽性菌。氯化鈉保持滲透平衡。 顯色混合物含有兩種生色底物，能夠檢測兩種特定的酶，即β-半乳糖苷酶和β-葡萄醣醛酸酶。由大腸桿菌產生的β-半乳糖苷酶切割一種色原體，導致大腸菌落的粉紅色。由大腸桿菌產生的酶β-葡醣醛酸糖苷酶切割X-葡糖苷酸。 由於兩種色原（1,2,3）的切割，大腸桿菌形成深藍色至紫色的菌落。 b-葡萄醣醛酸酶陰性的大腸桿菌菌株（血清型O157：H7）產生粉紅色的菌落。其他能夠在（44±0.5）℃生長的革蘭氏陰性菌產生白色或無色菌落。 轉移1ml產物進行分析，將其十倍稀釋至無菌培養皿中。倒入12毫升培養基，充分混合併使其固化。 用4ml培養基覆蓋，使其固化並在43-45℃下孵育18-24小時。