Materials and equipment for determining whether samples of potable water contain harmful microbes have been packaged in a kit. Designed for use aboard spacecraft, the kit is also suitable for terrestrial use in a laboratory or in the field. The kit holds the sample, nutrient, and waste liquids in a closed system.

A Water Sample Is Filtered through a microbial capture device. A nutrient solution is then injected into the device, and the device is incubated. After incubation, the number of colonies that grew from the captured microbes is counted.
The kit is based on a traditional technique that involves membrane filtration to separate microbes from the water sample, followed by growth of the microbes under favorable nutrient and temperature conditions. The resulting colonies of microbes are counted and recorded as an indication of the microbial content of the sample.

A water sample is collected in a small plastic bag. The bag is then connected to one end of an adapter unit that includes a valve. The other end of the adapter unit is connected to the inlet of a microbial capture device, which is a small in-line-filter chamber that contains (1) a cellulose acetate filter with an effective pore size of 0.45 μm and (2) an absorbent pad for subsequent retention of a nutrient solution in contact with the filter. A syringe pump and a waste bag are connected to the outlet of the microbial capture device; the syringe pump is used to draw sample water from the collection bag through the filter and into a waste bag (see figure). As sample water flows through the filter, microbes from the water become trapped in the filter.

Once the specified amount of sample water (typically, 100 mL) has been drawn through the filter, the microbial capture device is disconnected from the other devices. The nutrient solution, which is prepackaged in a syringe, is injected into the microbial collection device, which is then placed in an incubator at a temperature of 30°C, or else left at room temperature, if an incubator is not available. After incubation for 48 h at 30°C or 72 to 96 h at room temperature, the filter is examined; the number of bacterial colonies (which appear as blue dots) is counted and recorded.

This work was done by Duane L. Pierson and Richard L. Sauer of Johnson Space Center and David W. Koenig, D. Bell-Robinson, S. M. Johnson, and Saroj K. Mishra of Krug Life Sciences, Inc.


NASA Tech Briefs Magazine

This article first appeared in the September, 2002 issue of NASA Tech Briefs Magazine.

Read more articles from the archives here.