Abstract
The sensitivities of 3 test methods, LB-BGBL and 2 chromogenic substrate medium methods (minimal medium o-nitrophenyl-D-galactopyranoside-4-methyl-umbelliferyl-β-Dglucuronide: MMO and 5-bromo-4-chloro-3-indolyl-β-D-galactopyranoside: X-GAL methods) for the detection of E. coli and coliforms present in spring water were compared. A total of 158natural spring water and simulated spring water samples were examined.
The pH range for the bacteria to grow in LB-BGLB was 4.5-9.5, while that in chromogenic substrate media was 5.0-9.0. It was found that Na2S (equivalent to≥50mg/l of H2S) and Cu (≥20 mg/l) in the culture media inhibited the growth of bacteria. Complete coincidence of the results by the 3 test methods was obtained for the detection of E. coli, while, 92.4%coincidence was obtained for coliforms. The coincidences between the 2 test methods for coliforms were between 92.4% and 94.3% with the highest coincidence found between the MMO and X-GAL methods. The practical use of the MMO and X-GAL methods was evaluated. The culture media in the positive reaction by the MMO method turned yellow which sometimes caused difnculty when reading the results, since many natural spring water samples were slightly yellow. A positive reaction by X-GAL turned blue which was easier to read, thus the X-GAL method may be superior over the MMO method.
These results indicate that the chromogenic substrate medium methods are rapid and easy and can be used for the detection of E. coli and coliforms in spring water if pH, H2S and Cu are properly adjusted.
