EE&T  |  AwwaRF
  Home > Utility Strategies for Source Water Protection > Source Water Monitoring > Microbiological Analyses

 *Source Water Protection


Microbiological Analyses

Microbiological analyses are used to identify and quantify bacteria, viruses, protozoa and other potentially harmful pathogenic microorganisms. Conventional methods involve three steps for detecting and identifying microorganisms: (1) recovery and concentration of the target species, (2) purification and separation of the organisms, and (3) detection and identification.

Even though relatively easy-to-identify indicator organisms are often used for indicating the potential presence of more harmful microbes, significant drawbacks to analytical methods for microbes still exist in terms of their applicability for early warning monitoring applications. The primary weakness of conventional methods of microbial analysis is the relatively long time period required for isolation and reproduction (amplification) of the microbiological species, often a day or more. In addition, many tests are specific only to a single species or class of organism, while raw waters can contain a wide variety of pathogens.

General sources of information on conventional methods for the detection and measurement of microbial species are found in USEPA methods, Part 9000 of Standard Methods (APHA et al., 2005), Baker and Bovard (1996), and many other sources. Rose and Grimes (2001) reviewed recent developments in microbial analysis. A recent review of emerging pathogens also included discussion of analytical methods for their detection in water (AWWA Microbiological Contaminants Research Committee, 1999a and 1999b). Rapid detection methods for microbes are summarized in Venter (2000) and in Section 9211 of Standard Methods (APHA et al., 2005).

The microbiological quality of drinking water has for years been assessed through detection of indicator bacteria such as total coliforms, E. coli, or heterotrophic plate counts (HPC). Conventional methods involve cultural techniques that take 18 hours or more to perform. Recent advances in testing procedures have reduced the analysis time down to the range of 4 to 8 hours or less (e.g., Prescott, 2000; Eccles et al., 1998; Lee and Deininger, 1999; Deininger and Lee, 1998). Commercial methods are often used that involve specific enzyme defined substrate technology for monitoring for total coliform and E. coli within 18 to 24 hours (e.g., Edberg et al., 1991; Edberg and Smith, 1994).

Among the many protozoan parasites of concern to the drinking water industry are Giardia and Cryptosporidium. Giardia as been known for years to cause severe diarrhea and related problems in humans. Cryptosporidium is comparatively new to the water industry, and has caused several major outbreaks of Cryptosporidiosis over the last decade or so. Even though commercial kits are available that simplify the concentration step using immunomagnetic separation systems, the USEPA-approved methods (1622 and 1623) require extensive training for their immunofluorescence microscopy technique.