ATP assay still one of relaible method to quantify metabolic bacterial activity mainly in sediments but you should compare metabolic measurments with flux cytometer  that can be mre specific.

The variability is probably from how the samples are handled before you quench metabolism. The trick with ATP is rapidly stopping the metabolism while the cells still have ATP.  Remember, some bacteria completely turnover the ATP pool many times per second. If you take a sample and put it on ice or something, all the ATP will be converted to ADP before you measure it.  I quench metabolism with perchloric acid, which instantly stops metabolism by dissolving all the protein, but it leaves small molecules like ATP intact.

Thanks Michael, I work with biofilm on material's surfaces, so basically I have to sonicate the specimens in 0.9% saline solution to collect the biofilm. After that I take 100ul of my suspension and mix it with Bac titer ATP reagent (Promega). I'm always concerned about being too slow on doing this steps.

Do you have any protocol for using pechloric acid to share? I'd appreciate it .

Thanks!

 Perhaps you could sonicate in something that would quench metabolism instead of 0.9% saline.  Perchloric acid would destroy your sonicator probe, but maybe methanol.

The ATP method I use is described in a 2005 paper on my RG page... I think I can attach it here.

Good luck!

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