# Microcalorimetry--Versatile Method of Describing Bacterial Growth
The ability of bacteria to develop biofilm is known, which gives them resistance to antibiotic treatment and the host's immune system [10,11]. The generation of biofilm, both at the interface with the bone and at the interface with the implanted material, is also a problem in establishing the correct diagnosis. A number of techniques have been studied in an attempt to increase the chance of correct identification. [PERSON] et al. recommend the collection of at least three samples from different areas of the operating field, and they must be sown on both aerobic and anaerobic culture media [9,12,13]. Other authors describe increasing the specificity to over 90% and the sensitivity to over 80% by introducing the synovial fluid into a culture tube on a blood culture medium, together with at least one more sample collected, and investigated by classical laboratory methods [14,15]. Molecular biology methods for DNA/RNA identification and implant sonication are new techniques that appear to facilitate the diagnosis of orthopedic infections [9,16]. Microcalorimetry, as a science, dates back to the 18 th century, when microcalorimeters were used to record the heat emitted by various small animals. They have become more and more sophisticated, with various possibilities to record the temperatures produced in relation to them, as well as to the environment. The current microcalorimetry devices have the ability to record thermal energy of very low intensity, being one of the most sensitive methods of bacterial identification, theoretically managing to identify the energy produced by only 6250-25,000 microorganisms/mL. The vast majority of bacteria are prokaryotes and, according to studies, a single bacterium can produce 1-3 pW in the case of anaerobic growth [17,18] and 1-4 pW in the case of aerobic growth [19,20]. Microcalorimetry has the ability to identify a pathogen, with a short latency of about several hours, even if it is very diluted in the environment from which the sample is made, due to exponential replication [21; 22; 23]. This capacity increases with the improvement of the technical data of the apparatus used and is influenced by the experimental conditions, the culture medium, and the bacterial species [23; 24; 25; 26]. Calorimetry becomes useful in medicine because, due to the active metabolism of living organisms, they produce heat, which can provide interesting information in many bioanalyses [27; 28]. To date, numerous tests have been performed on living structures, which have presented interesting data. Microcalorimetry has been used to identify infections but also to verify the susceptibility of pathogens to antibiotics [29]; this technique has also been used successfully in interpreting parasite growth or food degradation [30]. Following microcalorimetric studies on bacterial growth, several stages of bacterial development have been defined depending on their metabolism, information that is useful in the detection of microorganisms. Studies using strains of Escherichia coli [31] or Lactococcus lactis [32] in environments with different glucose concentrations and under aerobic conditions have shown that a bacterial population emits a different amount of heat during growth processes, directly linked to the environmental factors present at the time of the experiment, which is easy to see in the growth curves generated by these bacteria. In the case of studies conducted by [PERSON] et al., experiments were performed with high glucose concentrations (50-100 g/L) in which the bacterial growth was stopped due to the very low pH of 4.3 (probably developed by bacterial excretion), and, in the case of a low concentration of glucose (2 g/L), the growth was stopped by the depletion of food sources. It is interesting to note that, although due to the different concentration of glucose, the energy released was higher under the conditions described in the first point, yet the growth curves show the same pattern of arrangement, being able to ensure bacterial identification [30; 32].