Enumeration of enterococci in New Zealand waters and effluents

Abstract

Samples of New Zealand effluents and receiving waters were analysed for enterococci by the USA Environmental Protection Agency membrane filter method. Enterococcus counts were typically an order of magnitude lower than corresponding faecal coliform counts. Pinprick‐size colonies were a problem in minimally treated effluent samples analysed by this method. These colonies required verification to obtain an accurate count. Similar samples were also analysed for Enterococci by an In‐house MPN method, developed for turbid samples. The In‐house method, which involves presumptive isolation in azide dextrose broth and confirmation on the media used for the membrane filter method, was found to be simple to use and to give satisfactory results. Quality control tests, also described, found that this method performed similarly to the membrane filter method and also to an MPN method recommended by the American Public Health Association for Enterococci. Effluents could be analysed by this method without problems of misidentification. Use of the In‐house MPN method in conjunction with the membrane filter method would allow laboratories to respond rapidly to changing environmental conditions.

Keywords:

• Enterococcus
• membrane filtration
• MPN
• receiving waters
• effluents