Towards faster identification of MRSA and MSSA: analysis of calorimetric curve parameters from large hospital bacterial collections

There is a need to develop faster yet precise diagnostic tools for the identification of infectious agents and their levels of antimicrobial susceptibility. One such tool is calorimetry, as previous studies show that bacteria display unique signatures of calorimetric/metabolic activity that such signatures can be used for pathogen identification under controlled laboratory conditions. However, the level of variation of these unique signatures remains largely unexplored. Here, we use real-time isothermal microcalorimetry to disentangle the inter- and intra-species metabolic differences between S. aureus and S. epidermidis. We worked with a large collection of bacterial isolates obtained from patients with prosthetic joint infections as well as reference laboratory strains. We analyzed their calorimetric profiles and decomposed the curve parameters derived from them. As a result, we identified six calorimetric parameters that are useful for identification at the intra-species level, with a particular focus on MRSA. Furthermore, we found important differences between the thermograms of ATCC laboratory strains when compared against model thermograms generated from all our clinical isolates. These results indicate that accounting for metabolic variability can impact diagnosis precision. Finally, we discuss our findings and suggest ways to optimize calorimetric diagnostics and treatment approaches.