Validation of respirometry as a short-term method to assess the efficacy of biocides

Abstract

This study shows that a short-term respirometric measurement based on the rate of oxygen uptake needed to oxidize glucose is a reliable and fast method to assess biocide efficacy against P. fluorescens cells. Respiratory activity using oxygen consumption rate, the determination of viable and nonviable cells using Live/Dead^® BacLight™ kit and colony formation units (CFU), were compared as indicators of the biocidal efficacy of ortho-phthalaldehyde (OPA). The results showed that determining the effect of OPA against P. fluorescens using the different methods leads to different conclusions. The minimum bactericidal concentration (MBC) was 80 mg l⁻¹, 100 mg l⁻¹ and 65 mg l⁻¹ respectively, using respiratory activity, viability using BacLight counts and culturability. The plate count method was shown to underestimate the biocidal action of OPA, whilst data from respirometry and viability using Live/Dead BacLight kit correlated strongly and were not statistically different when yellow cells were considered nonviable. Respirometry therefore represents an expeditious, non-destructive and accurate method to determine the antimicrobial action of biocides against aerobic heterotrophic bacteria.

Keywords:

• Respiratory activity
• Live/Dead BacLight™
• culturability
• viability
• disinfection
• biocide

Acknowledgements

The authors acknowledge the financial support provided by IBQF and FCT, and the Portuguese Foundation for Science and Technology, through the project POCTI/1999/BIO/35683 and PhD grant awarded to Manuel Simões.