Abstract
Using differential scanning calorimetry (DSC) and plate count (PC), growth of Escherichia coli was measured in four initial E. coli cell concentrations cultured in tryptic soy broth (TSB) at 35°C. The calorimeter measured the energy released and/or absorbed by E. coli cells during growth and expressed it as thermograms. The resulting thermograms accurately reflected cell growth and activity, and exhibited a close correlation with growth values recorded by PC. Heat release decreased notably in the final stage of the logarithmic growth phase, and no signal was generated once the stationary phase had begun. DSC accurately quantified growth in E. coli at different initial cell concentrations grown in TSB at 35°C. Depending on initial E. coli concentration, DSC detected growth starting after just a few minutes and up to five hours. The detection limit of calorimeter was 4.3 ± 0.4 log10 CFU. DSC is an effective alternative method for measuring bacterial growth in TSB in real time. This is the first report of DSC use for measuring bacterial growth. Key words: Differential scanning calorimetry (DSC), Escherichia coli, thermograms
Highlights
Plate count and turbidimetric (e.g. Bioscreen C) are the most commonly used techniques to monitor microbial growth (Huchet et al, 1995)
Signal onset is related to heat generation, which can be associated with microbial activity
E. coli grew well in TSB at low oxygen levels and under these conditions the thermograms showed it to exhibit a hyperbolic growth pattern (Figure 1). This coincides with a previous report of hyperbolic growth in E. coli when metabolizing glucose and with use of a calorimetric pump (Boe and Lovrien, 1990)
Summary
Plate count and turbidimetric (e.g. Bioscreen C) are the most commonly used techniques to monitor microbial growth (Huchet et al, 1995). Microcalorimetry can measure changes in heat released and/or absorbed during bacterial growth (Boe and Lovrien, 1990; Braissant et al, 2010a; 2010b; Von et al, 2009), and has been used to monitor growth of E. coli in broth under different culture conditions. The present study objective was to measure E. coli growth in tryptic soy broth at 35°C by both differential scanning calorimetry (DSC) and plate count (PC), and compare the resulting data.
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