Colilert® is a one-step method for water quality and compliance testing, giving results for total coliform and Escherichia coli in 18 or 24 hours with less than 1 minute of hands-on time. Colilert has a full range of regulatory approvals and has become the perfect test for a wide variety of source water applications, including required regulatory compliance testing, bottled water testing, and for fresh-cut produce or fruit rinse water (before or after processing).

Approvals and recognitions include:

•    FDA/NCIMS/PMO for total coliform for plant and farm source waters; recognized for use by certified milk laboratories for negative and positive confirmation for total coliform testing

•    USEPA, AOAC, and IBWA approved for total coliforms and E. coli

•    Accepted by APHA Standard Methods for the Examination of Water and Wastewater for total coliforms and E. coli

Colilert is pre-measured, unit dosed, and ready to use with clear, easy-to-read colorimetric results. It detects a single viable coliform or E. coli per sample. The sample collection, incubation, and reading can all be done in the same vessel. Colilert can be used as a presence/absence test for total coliforms and to specifically identify the presence or absence of E. coli through fluorescence with definitive results in 24–28 hours. Quanti-Tray® can be used for the added benefit of quantification of results. An 18-hour version allows the user to read afternoon samples the next morning—before the next day’s samples arrive. “I’m thrilled to learn about this test!” is the most common comment from new Colilert users, reports Weber Scientific sales manager Asif Rahman.

How Colilert Works
The Colilert test uses proprietary Defined Substrate Technology (DST) to simultaneously detect total coliforms and E. coli. Two nutrient-indicators, ONPG and MUG, are the major sources of carbon in Colilert and can be metabolized by the coliform enzyme β-galactosidase and the E. coli enzyme β-glucuronidase, respectively. As coliforms grow in the Colilert test, they use β-galactosidase to metabolize ONPG and change the water color from colorless to yellow. E. coli use β-glucuronidase to metabolize MUG and create fluorescence. Since most noncoliforms do not have these enzymes, they are unable to grow and interfere. The few noncoliforms that do have these enzymes are selectively suppressed by the Colilert test’s specifically formulated matrix.

This approach is different from traditional media, which provide a nutrient-rich environment that supports the growth of both target organisms and nontargets. When nontargets grow and mimic target organisms, false positives occur. Growth of nontargets can also suppress target organisms and give false negatives in traditional media. How the Colisure Test Works

Colisure® also detects coliforms and E. coli but with the convenience of a long-read window and a definitive color change for both positive and negative results. A distinct magenta color means there’s no mistaking a positive result. Results are definitive at 24 hours with a read window that lasts up to 48 hours and can be used for presence/absence or quantification testing with Quanti-Tray. “This technology is truly the gold standard of rapid coliform in water testing,” according to Sharon Wilson, Weber Scientific’s vice president of marketing and product development. The Colisure test uses proprietary DST nutrient indicators CPRG and MUG to detect total coliforms and E. coli.

Automated Water Sample Handling for Coliform and E. coli Quantification
The Quanti-Tray Sealer PLUS is the next-generation sealer in the Quanti-Tray system. The sealer makes quantification with Quanti-Tray and Quanti-Tray/2000 possible while saving time and improving laboratory efficiency.

With Quanti-Tray, a 100-mL sample is divided into 51 wells. Then the most-probable-number approach is used to determine the number of bacteria in the original sample. Automation minimizes hands-on time and maximizes throughput (up to four samples per minute). The relatively large number of wells provides a high counting range of 1–200 (without dilutions) and very tight 95 percent confidence limits.

The Quanti-Tray/2000 is based on the same statistical model as the traditional 15-tube serial dilution. With the Quanti-Tray/2000, the sample is automatically divided into the proper portions when sealed by the Quanti-Tray Sealer PLUS. The system does not require the use of test tubes, Durham tubes, or any dilutions. By automatically distributing the sample into 97 wells of two different sizes, Quanti-Tray/2000 yields a counting range of 1–2,419 CFU/100 mL with a far better 95 percent confidence limit than a 15-tube serial dilution.

Weber Scientific is an authorized distributor of IDEXX products to the food and beverage industries in the U.S. and Canada.