Laboratory Service Performed: Evaluation of the Bacteriostatic Properties of a Water Treatment Device Containing an Alloy of Copper and Zinc (KDF® media)
|Introduction:||Water treatment devices may be colonized by bacteria and thus promote the growth of bacteria contained in the influent water. It is important, therefore, that devices that are intended for use in potable water supplies be tested to determine if they are bacteriostatic (i.e. do not stimulate the growth of microorganisms).|
The testing protocol used is described in
Table 1. This procedure provides a heavy bacterial
challenge over a seven day period followed by a period of time to allow the
growth of the challenge bacteria. If the treatment device provides an
environment that is favorable for bacterial growth, there should be a
demonstrable increase in bacterial numbers during the latter stages of the
The supply water for the model system was chlorine free deionized water that was reconstructed to approximate Detroit city water by the injection of AOAC synthetic hard water to achieve a final concentration of 100 ppm and a pH value of 7.0
A fresh suspension of Enterobacter aerogenes (former name Aerobacter aero genes) was prepared daily and injected into the flowing water stream to achieve a final bacterial concentration of 300 cfu/ml.
|Results and Discussion:||
The results of the 19 day bacterial challenge test are shown in
Table 2. For the first seven days Enterobacter was
injected into the influent water stream and the survivors that passed
through the test device were measured. There were endogenous bacteria
(naturally occurring water bacteria other than Enterobacter) present in the
model water system at the beginning of the testing, and there was a large
reduction in these bacteria as a result of passage through the water
treatment device. The results shown in Table 2 for the first seven days of
testing show the Enterobacter survivors only. The measurements after 11 and
19 days, during which time no additional Enterobacter was injected into the
system, the results in Table 2 show the percent reduction in these
endogenous bacteria (no Enterobacter survivors were detected).
This testing showed that the water treatment device is bacteriostatic and does not stimulate the growth of Enterobacter nor does it provide an environment that promotes survival. In addition, the device is effective in reducing the concentration of Enterobacter or other endogenous bacteria present in the influent water (bactericidal effect) and thus may be useful in the control of potentially harmful bacteria that may inadvertently enter potable water supplies.
Submitted by John W. Wireman, PhD
Dated February 25, 1991
View Table of Results For Removing Enterobacter Aerogenes Bacteria.