Isolation of Fecal Bacteria from Water Samples by Filtration

Source: Laboratories of Dr. Ian Pepper and Dr. Charles Gerba - The University of Arizona
Demonstrating Author: Luisa Ikner

The quality of water destined for use in agricultural, recreational, and domestic settings is of great importance due to the potential for outbreaks of waterborne disease. Microbial agents implicated in such events include parasites, bacteria, and viruses that are shed in high numbers in the feces of infected people and animals. Transmission to new and susceptible hosts may then occur via the fecal-oral route upon ingestion of contaminated water. Therefore, the ability to monitor water sources for the presence of pathogenic microorganisms is significant in order to ensure public health.

Due to the sheer number and variety of potential fecal-oral pathogens that may be present in water and their variable concentrations, it is impractical and expensive to assay directly for each one of them on a regular basis. Therefore, the microbiological assays for water quality monitoring employ coliform indicator bacteria. Coliforms comprise, in part, the normal intestinal microflora of warm-blooded mammals, are non-pathogenic, and are consistently excreted in the feces. Therefore, the detection of coliform bacteria in water means that a fecal release occurred, and that harmful pathogenic microorganisms may also be present.

1. Water Sample Collection and Processing

Collect several 1-L water samples from the test water source (e.g. water fountains, swimming pools, reservoirs, water distribution systems, raw or treated sewage), and transport on ice to the laboratory for microbial analysis.
Sterilize or sanitize the membrane filtration manifold assembly prior to use by autoclaving, exposure to UV radiation (2 min), or ethanol-flame ignition.
Upon cooling of all parts, properly connect the manifold to a

Membrane filtration is used in virus capture and concentration from water. Human pathogenic viruses carry a net negative charge in aquatic solutions, and are often present at low levels in water sources. Therefore they must be concentrated prior to analysis. Membrane filtration is but one capture method for this purpose, and employs a negatively-charged filter. Water samples (e.g. 1-L) of interest are amended with a salt solution (e.g. magnesium chloride) to impart a positive charge to the viruses, ther

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