Evaluation of Fluorocult Laurylsulfate X-GAL Broth for Enumeration of Coliforms and Escherichia coli.

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Fluorocult laurylsulfate X-GAL broth (LMX) containing a chromogenic substrate, 5-bromo-4-chloro-3-indolyl-β-D-galactopyranoside (X-GAL), for detection of coliforms and a fluorogenic one, 4-metylumbelliferyl-β-D-glucuronide, for detection of Escherichia coli was used for enumeration of these microorganisms in environmental specimens and the medium was compared with a conventional medium, BGLB, and another chromogenic medium, Colilert. The most probable numbers (MPN) of total coliforms, fecal coliforms and fecal E. coli obtained with LMX and BGLB showed a good correlation, but that of total E. coli obtained with LMX was higher than that with BGLB, so the former medium was more sensitive than the latter in detection of E. coli. LMX can simultaneously detect coliforms and E. coli, but the detection of E. coli with BGLB required 5 to 6 days because of the necessity of the confirming tests. Moreover, in comparing LMX and Colilert, MPN of total coliforms and total E. coli were correlated. With some samples, the color of X-GAL in LMX changed more slowly than 2-nitrophenyl-β-D-galactopyranoside in Colilert, and it seemed that the use of a water bath is preferable for incubation of LMX. Therefore, LMX may be useful and convenient for detection and enumeration of coliforms and E. coli.
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