Quantitative determination of Escherichia coli in water using CHROMagar® E. coli

A new medium, CHROMagar® E. coli (CAEC), containing a combination of X-glucuronide and methyl-glucuronide for the detection of β-glucuronidase activity of Escherichia coli has been evaluated by the membrane filtration (MF) technique n fresh water samples. The CAEC agar was compared with conventional media, mFC agar and mLSB, for the enumeration of faecal coliforms. The variance analysis showed that CAEC was as sensitive as mFC agar and mLSB. A good correlation was found between E. coli versus those from faecal coliforms in the water sampling areas tested. Of 321 presumptively positive E. coli colonies (blue) and 154 presumptively negative E. coli colonies (white), only 8 (2.5%) false positive and 19 (12.4%) false negative colonies were found. Specificity of the CEAC agar in spanish samples was temperature dependent, false negative E. coli colonies occurred less frequently at 37°C (2.3%) than at 44.5°C (18.8%). The results of this study indicate that CAEC agar is efficient for the enumeration of E. coli from a wide range of environmental freshwater samples.