HiMedia – M1294and2056_HiCrome™ ECC Selective Agar Base Modified

Principle and Interpretation
These are selective medium recommended for the simultaneous detection of Escherichia coli and total coliforms in water and food samples (1, 3). The chromogenic mixture contains two chromogenic substrates. The enzyme b-D-galactosidase produced by coliforms cleaves one of the chromogen to form salmon to red coloured colonies(4). The enzyme b-D-glucuronidase produced by E. coli, cleaves X-glucuronide, the other chromogen (5). E. coli gives dark blue to violet coloured colonies due to cleavage of both the chromogens. Addition of L- Tryptophan improves the indole reaction, thereby increasing the detection reliability. Peptone special, Peptone, Tryptone and sodium pyruvate provide nitrogenous substances, carbonaceous compounds, long chain amino acids, vitamins and other essential growth nutrients for the organisms. Sorbitol is the fermentable carbohydrate. Phosphates buffer the medium. The media formulation helps even the sublethally injured coliforms to recover and grow rapidly. Tergitol in M1294 inhibits gram-positive as well as some gram-negative bacteria other than coliforms (3). Sodium lauryl sulphate in M2056 inhibits gram-positive organisms. Addition of HiCrome™ ECC Selective Supplement (FD190) in M1294 helps to inhibit the accompanying heterogenous microflora. The medium is inoculated either by pour plate technique or by spreading the sample on the surface of plated medium. Membrane filter technique can also be used. Other gram negative bacteria forms colourless colonies, except some organisms which are b-glucuronidase positive. b-glucuronidase positive organisms gives light blue to turquoise colonies. Glucuronidase is present in 94–96% of E. coli strains and in some Salmonella, Shigella and Yersinia spp (2). To confirm E. coli, add a drop of Kovac’s reagent on the dark blue to violet colony. Formation of cherry red colour indicates a positive reaction.

原理與解釋
這些是推薦用於同時檢測水和食物樣品中大腸桿菌和總大腸菌的選擇性培養基（1,3）。顯色混合物含有兩種生色底物。由大腸桿菌產生的酶b-D-半乳糖苷酶切割一種色原體，形成鮭魚色至紅色色澤的菌落（4）。 由大腸桿菌產生的酶b-D-葡醣醛酸糖苷酶切割X-葡糖苷酸，另一種色原體（5）。由於兩種色原的裂解，大腸桿菌產生深藍色至紫色的菌落。 L-色氨酸的添加改善了吲哚反應，從而提高了檢測可靠性。 蛋白腖，蛋白腖，胰蛋白腖和丙酮酸鈉為生物體提供含氮物質，含碳化合物，長鏈氨基酸，維生素和其他必需的生長營養素。 山梨糖醇是可發酵的碳水化合物。磷酸鹽緩衝培養基。培養基配方甚至可以幫助受亞致死傷害的大腸菌群恢復並迅速生長。 M1294中的Tergitol抑制革蘭氏陽性以及除大腸桿菌外的一些革蘭氏陰性細菌（3）。 M2056中的十二烷基硫酸鈉抑制革蘭氏陽性菌。 在M1294中添加HiCrome™ECC選擇性補充劑（FD190）有助於抑制伴隨的異源微生物群落。 通過傾注平板技術或通過將樣品鋪展在電鍍培養基的表面上來接種培養基。也可以使用膜過濾技術。除了一些β-葡萄醣醛酸酶陽性的生物外，其他革蘭氏陰性細菌形成無色菌落。 β-葡萄醣醛酸酶陽性生物體給予淺藍色至綠松石菌落。葡萄醣醛酸酶存在於94-96％的大腸桿菌菌株和一些沙門氏菌，志賀氏菌和耶爾森菌屬中（2）。為確認大腸桿菌，在深藍色至紫色菌落上加入一滴Kovac試劑。 櫻桃紅色的形成表示陽性反應。