Heat-Transfer Method: A Thermal Analysis Technique for the Real-Time Monitoring of Staphylococcus aureus Growth in Buffered Solutions and Digestate Samples

The identification and quantification of microorganisms in water samples are crucial to improve processes in organic waste treatment facilities. Most of the currently available tests are either labor intense or costly, and they do not allow determination of the dynamics within microbial communities in digestate samples. This study is the first report on the use of thermal analysis, specifically the heat transfer method (HTM), to monitor microbial load in aqueous systems and digestate samples. Staphylococcus aureus was used as a model organism, and different concentrations in water were measured by the HTM. It was demonstrated that there was a positive correlation between the thermal resistance and concentration of the bacterial cells. Subsequently, the influence of temperature on growth rates was studied and confirmed by plating experiments and scanning electron microscopy (SEM). These results showed the possibility to monitor the temperature-dependent growth of S. aureus using the HTM. To determine if this technique can be applied for studying complex matrices, digestate samples were collected from a number of sources and plated on nutrient agar plates. The bacterial cultures derived from single colonies were characterized and identified by sequencing of DNA regions for 16S rRNA. HTM measurements were performed in diluted or centrifuged digestate samples that were enriched with S. aureus. The results indicated that it is possible to evaluate microbial load even in samples containing other organic material. The thermal analysis method has the potential to provide a low-cost monitoring option, which is simple to use and provides real-time analysis, thus improving the existing monitoring procedures in organic waste treatment facilities.