There is a well known but forgotten heat measuring apparatus, an isothermal microcalorimeter (Fast4U Calorimeter built by Calbact AG) that can be used to obtain the dynamic heat-flow produced during a bacterial infection. It allows susceptibility testing to be done in shorter time than with conventional methods.

The result of a heat-flow curve produced e.g. the one produced at the threshold level by 10⁵ CFU one gets what otherwise uses multiple steps.

• Is there a bacterial infection in some bodily fluid? Yes, if heat is produced.
• Can one differentiate between living bacterial and a viral infection? Yes, there is no heat in a viral infection.
• Is there a spread of bacteria into the bloodstream or in the urine (Urinary track infections) or in other body fluids? Yes, if a distinct heat-flow curve is displayed.
• What are the type of bacteria? Heat-flow curves have distinct, bacteria specific shapes.
• Which antibiotic and appropriate Minimal Inhibitory Concentration (MIC) is killing the bacteria (antibiogram)? Bacteria in the presence of an antibiotic with the appropriate MIC added to the sample almost eliminates the heat-flow.

The influence of antibiotics on heat-flow curves will be shown. These modifications indicate the effect caused by the resistivity.