Beach Health & Water Quality

Beach Monitoring Techniques

How do you test for harmful micro-organisms?

The most basic test for microbial contamination is the test for total coliform bacteria. Total coliforms include bacteria found in human and animal waste (fecal coliforms) as well as bacteria that occur naturally in water and soil. Total coliform (TC) counts give a general indication of the sanitary condition of the water. Fecal coliforms are the group of coliform bacteria present specifically in the gut and feces of humans and animals. Because the origins of fecal coliforms are more specific, fecal coliform counts are a better indication of fecal pollution than TC counts. E. coli is both the dominant species of the FC group and the only coliform species that cannot grow or reproduce in the environment. Consequently, E. coli is the best-suited coliform species to serve as an indicator of fecal pollution and the possible presence of pathogens.

E. Coli Test

Dozens of different laboratory protocols exist to detect and count E. coli in water samples. But most of them are based on the same principle. A water sample is collected and passed through a membrane filter, which retains any bacteria. From there, a three-step procedure employs selective and differential growth media to identify E. coli based on biochemical traits.

    Step 1: E. coli has the necessary enzymes to use the sugar-like compound lactose as an energy source, whereas many other bacteria lack them. The initial step of the E. coli test usually employs selective growth media that contain lactose as the sole source of carbon. The lactose medium allows only lactose-positive bacteria (Lac+) to grow. Lac+ bacteria include E. coli and several other fecal coliforms. An incubation temperature of 44?C favors growth of E. coli over other Lac+ bacteria.

    Step 2: It is usually a color or fluorescence test to differentiate fecal coliforms from other Lac+ bacteria. It uses chemicals that react with certain substances excreted by E. coli and other fecal coliforms to form color or fluorescing compounds.

    Step 3: a number of additional enzyme-based tests help differentiate between E. coli and other fecal coliforms.

    Rapid testing Procedures

    Some recently developed methods may cut the wait for E. coli results from days to hours or even minutes. The Rapid Automatic and Portable Fluorometric Assay System can be hand-carried to the lake and is capable of determining levels of E. coli in as little as 10 minutes. The equipment, which was developed by the U.S. Navy to test for biological contamination, weighs less than 10 pounds. Essentially, the system employs antibodies with fluorescent tags that attach to the sought after bacteria. Virtually any type of bacteria can be tested for with this type of equipment as long as an antibody for the bacteria is available. But at least for the immediate future, the antibodies are limited.

    Polymerase Chain Reaction (or PCR, in short), the same technology currently used in paternity cases and to solve crimes, can also be applied to testing for beach water quality. With this method, very small amounts of bacterial DNA--even of a single cell--can be traced by amplifying them in a chain reaction using DNA polymerase, an enzyme that knits copies of DNA from a template DNA strand. In this detection method, one of the four basic buildings blocks of DNA--called nucleotides--can be tagged with a fluorescent so that the newly formed DNA emits a signal. Researchers can then use that signal to measure how much bacteria they started with, thereby determining the bacteria levels in the water.