Use of isothermal microcalorimetry to monitor microbial activities

Abstract

Isothermal calorimetry measures the heat flow of biological processes, which is proportional to the rate at which a given chemical or physical process takes place. Modern isothermal microcalorimeters make measurements of less than a microwatt of heat flow possible. As a result, as few as 10 000-100 000 active bacterial cells in culture are sufficient to produce a real-time signal dynamically related to the number of cells present and their activity. Specimens containing bacteria need little preparation, and isothermal microcalorimetry (IMC) is a nondestructive method. After IMC measurements, the undisturbed samples can be evaluated by any other means desired. In this review, we present a basic description of microcalorimetry and examples of microbiological applications of IMC for medical and environmental microbiology. In both fields, IMC has been used to quantify microbial activity over periods of hours or even days. Finally, the recent development of highly parallel instruments (up to 48 channels) and the constantly decreasing costs of equipment have made IMC increasingly attractive for microbiology. Miniaturization of isothermal calorimeters provides an even wider range of possibilities.

In vitro inhibition of Clostridium difficile by commercial probiotics: A microcalorimetric study

“…IMC is an established technique for monitoring bacterial growth (Braissant et al, 2010). It produces net metabolic heat output proportional to growth and characteristic for different species of bacteria (Beezer, 1980;Braissant et al, 2010).…”

“…The aim of the study was to investigate the influence of some commercial probiotics on the growth of C. difficile using the isothermal microcalorimeter (IMC), an instrument which has been established to measure bacterial growth in real time by monitoring net metabolic heat output, giving characteristic signatures for individual bacteria that are proportional to their growth (Beezer, 1980;Braissant et al, 2010;6 Said et al, 2014). Noteworthy, traditional in vitro methods to study the effect of probiotics against intestinal pathogens involve either a broth culture or an agar diffusion assay (Lee et al, 2003;Naaber et al, 2004;Schoster et al, 2013).…”

Biofilm formation by staphylococci on fresh, fresh-frozen and processed human and bovine bone grafts

“…TTD correlated well with the cfu counts after sonication, thus these results are not a consequence of different amounts of bacteria being dislodged during the sonication procedure; Secondly, heat-flow curves with two peaks were only seen with fresh (3 h and 24 h incubation) and fresh-frozen (24 h incubation) samples and small colonies were only found for these samples, too. Heat flow curves represent an unspecific sum signal of exothermal and endothermal reactions within the calorimetry ampoules and might be affected by oxygen depletion and accumulation of metabolic waste (Braissant et al, 2010). Our experimental setting provided the same amount of TSB and oxygen to all samples, thus variations in the heat-flow curves should not be related to varying conditions in the ampoules.…”

Development of a flow system for studying biofilm formation on medical devices with microcalorimetry

“…These qualities make it ideally suited to the study of bacterial growth and metabolism in real-time. In particular, the exquisite sensitivity means as few as 10 4 metabolically active cells can be detected [1]. Further, it is possible to monitor bacterial activity in the presence of antimicrobial agents and/or medical devices and implants because there is no requirement for optical clarity of the test system.…”