CAN ATP-MEASUREMENTS REPLACE THE CLASSICAL COLONY COUNT 22oC IN
DRINKING WATER SAMPLES TAKEN AFTER REPAIR OR CONSTRUCTION WORKS?
Wim Hoogenboezem and Roland N. Tschumie
Postal Box 734, 2003 RS Haarlem, The Netherlands
[email protected]
Introduction
After construction or repair works in drinking water facilities or distribution mains tests are
required to assure the microbial quality (fecal indicators: E. coli (and coliforms), enterococci and
colony count 22 oC, Plate count agar (PCA). These are culture tests, for E. coli a PCRconfirmation test is in use. For enterococci cultures MALDI-TOF confirmation is available.
However, colony count 22 oC requires 72 hours (three days!). The obtained colony count number
results from a wide range of different microbial species. Therefore an approach using PCR is
complicated and probably not successful very soon. Estimation of microbial biomass using ATPmeasurements can be an appropriate rapid method for the evaluation of drinking water samples
taken after construction or repair works.
Methods
All organisms use Adenosine Tri Phosphate (ATP) as energy transfer compound in cellular processes. ATP is often used to
estimate microbial biomass. We studied 413 samples from practical situations (both construction and repair works). Samples
were taken and analyzed both by the classical culture method (colony count 22oC) and by measuring the microbial ATPcontent. The relationship between both parameters is analyzed by plotting the colony counts against the ATP values. The aim is
to find an ATP-value that coincide with the guidance level of 1000 cfu/ml, in order to set a critical ATP-value for the
evaluation of drinking water samples taken after construction or repair works.
Results
A scatterplot of 413 first day samples, the plot
is divided into four areas by the green line for
the current guide level (1000 cfu/ml) and the
red line represents the ATP-value (ng/l) that
could replace the guidance level of colony
count. Ideally the results are found in sections
B (rightfully rejected) and C (rightfully
accepted). The position of the red line is
adjusted to fit a minimal number (≤5%) of
results in sections A and D. Results in these
areas would lead to a wrong conclusion
regarding to the current colony count.
Discussion
As expected a distinct variation is seen in both colony counts and ATP-levels. Much of the variation can be explained by the fact
that colony count determination (PCA) shows only a small fraction of the viable bacteria present in water samples. On the
other hand dormant bacteria probably contain less ATP but may produce a colony in the PCA-medium. Both methods determine
(at least partly) different members of the microbial community. The present results, however, are comparable. It is important
to note that also the current method with PCA is prone to uncertainties. The ATP-method accommodates an important
advantage in time, using ATP it is possible to make the first microbial evaluation on the day that repair or construction works
have completed.
Conclusion: Yes we can!
ATP measured on the day of sampling provides a rapid and reliable microbial evaluation compared to colony count (22 oC). Our
results have shown: ATP can be used as an early warning system. High ATP (>10 ngL -1) value may indicate poor
construction/repair work, demanding immediate action.
The great advantage is that ATP-results provide microbiological indication on the water quality on the day of sampling, if
necessary corrective measures can be taken on the same day!