Flow cytometry as a tool for oilfield biocide efficacy testing and monitoring

• Flow cytometry has been validated as an effective method of biocide efficacy testing for oilfield systems.
• A comparison of classical culturing methods and flow cytometry showed that viability results showed strong correlation after biocide treatment; however, flow cytometry identified viable-but-nonculturable cells unaccounted for by serial dilution.
• A comparison of 2nd-generation ATP testing and flow cytometry showed that ATP testing significantly overestimated bacterial viability following biocide treatment.

Currently, oilfield biocide performance testing relies on classical microbiological culture techniques and culture-independent based methods such as ATP measurement. Although each method has its merits, there are significant drawbacks for each. For example, results from culturing require a two to four week incubation, which delays optimization of the biocide application. It also assumes that the microbes are able to grow in oilfield culture media. ATP photometry has reduced the time necessary for system optimization to one day, but there can be challenges with quantification of stressed and dying – yet intact – microbes. Flow cytometry is a technique that allows a real-time, absolute measurement of individual cells and gives insight into microbial kill mechanisms by distinguishing physiologic states other than alive or dead. Based on these advantages we show that flow cytometry may be a better alternative for biocide selection compared to culture- and ATP-based methods. Here we show that kill studies done with flow cytometry can give more meaningful and significant results compared to culture-based methods and commercially available ATP kits on pure-culture preparations and oilfield water samples.