Differentiation Between ${\varvec{Staphylococcus\,aureus}}$ and ${\varvec{Staphylococcus\,epidermidis}}$ Using Microcalorimetry

Abstract

Microcalorimetry is a highly sensitive experimental technique that determines heat changes in any process or transformation. All organisms produce heat due to their metabolism. The rate of heat flow is an adequate measure of metabolic activity of living beings and their component parts. Microorganisms produce small amounts of heat: 1 pW to 3 pW per cell. Although the heat produced by bacteria is very small, their exponential reproduction in a culture medium permits heat detection through microcalorimetry. A microcalorimetric growth and metabolic study was carried out for the bacteria Staphylococcus aureus and Staphylococcus epidermidis, by using heat liberated during metabolism. A thermal conductivity calorimeter of the Calvet type was used. The inside of the calorimeter contains two stainless steel cells (experimental and reference) with a screw-on Teflon cap with a hole in the center. Experiments were carried out with final concentrations of the order of $(10^{6}, 10^{5}, 10^{3}$, and 10) CFU$\,{\cdot }\,\text{ ml }^{-1}$. These were kept at a constant temperature of 309.65 K. The plot of change in heat voltage versus time enables acquisition of the characteristic growth curve for each bacterial strain. Thermograms were analyzed mathematically and helped determine the characteristic parameters for each microorganism, and led to the identification of the bacterial species.