Sample analysis
Water samples collected under the Beachwatch Programs are tested by commercial laboratories for the indicator bacteria, enterococci.
Bacterial testing is conducted using membrane filtration following Australian Standard method: AS/NZS 4276.9:2007. This method does not require a confirmation step (unless the plate is crowded) and results are available within 26 hours.
The procedure involves filtering a precise volume of the water sample through a very fine membrane to capture any bacteria present in the sample. The membrane is then placed on a special gel medium which promotes the growth of the indicator bacteria and incubated for 24 to 48 hours. During this time, each bacterium multiplies many, many times to form an individual colony that is visible to the naked eye. Enterococci colonies are generally red. The colonies are then counted to determine the number of indicator bacteria present in the volume of sample filtered. The results are reported as colony forming units per 100 millilitres of sample (cfu/100mL).
Due to the long incubation time required to grow the colonies, laboratory testing can take up to 48 hours to complete. As a result, laboratory results are not available for inclusion in the daily bulletins, but are used for all other reporting.
The laboratories used in the Beachwatch and Beachwatch Partnership programs are included in a quality assurance program and laboratory performance is reported in the Annual State of the Beaches Report.
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Page last updated: 15 February 2013
