How to speed up the detection of aerobic microbial contaminations by using isothermal microcalorimetry

Abstract

Isothermal microcalorimetry (IMC) is regarded as a promising diagnostic tool for fast detection of bacterial contaminations in various matrices. Based on a reference detection time determined by visual inspection of bacterial growth on solid medium, we investigated the strict aerobically growing Pseudomonas putida mt-2 KT2440 in a static 4-mL ampoule system on solid and liquid media by IMC to evaluate the three main options to reduce the detection time of bacterial contamination. Firstly, the sample preparation (e.g. membrane filtration) leads to an elevated number of bacteria in the measuring ampoule and thus to a reduced detection time. Secondly, the amount of substrate and oxygen has been investigated by varying the filling volume of medium in the calorimetric ampoule. Here, we were able to show how biophysical characteristics like the substrate and oxygen diffusion determined the shape of heat flow signals and thus the detection time. Finally, the technical framework determines the sensitivity of the IMC instrument. We examined the impact of four different detection threshold values (2, 10, 50 and 100 µW) on the detection time as a function of the initial number of bacteria presented in the ampoule and the filling volume.