Performance assessment of the two oxygen sensor based respirometric platforms with complex media and in selective bacterial assays

Abstract

Two common platforms currently used in respirometric microbial assays were evaluated comparatively with a panel of selective and differential media specific for E. coli, including the MacConkey (MC), M-Lauryl Sulfate (MLS), Minerals Modified Glutamate (MMG) and Rapid Coliform ChromoSelect (RCC) broths. The first automated platform is based on a soluble O2 probe MitoXpress, standard microwell plate substrate and time-resolved fluorescence reader detection. While operating stably in MC and MMG, it showed prominent interferences and instability in RCC and MLS media, due to phenol red dye and the surfactant largely attenuating the probe signal. The second platform, based on the longwave emitting solid-state sensor coatings deposited at the bottom of disposable assay vials and read with a handheld sensor reader Piccolo2. While having lower sample throughput and automation, this platform demonstrated stable operation in all the media, because its sensor dye PtBP is effectively shielded from interference by sample and media components making the assays stable and robust. Calibration functions for E.coli enumeration show linear relationship with measured Threshold Time (TT, hours): Log (CFU/mL) = a - b*TT, with a ranging 7.24–7.73 h-1 and b ranging 0.49–0.77 for the different selective media. These results help to choose the optimal respirometry platform for large-scale applications such as selective microbial assays and culturomics.