The presented statistical analysis indicates a reasonable turbidity GSK126 control of the inoculum, at least within the utilized experimental set. An alternative approach consists in taking, e.g., t0.015 as zero reference time for samples of different initial concentration (inoculum size) that would mimic the

hospital lab conditions. The thermal growth variability with inoculum size was explored in our previous contribution [7] involving freshly prepared inocula of S. epidermidis growth evaluated on the Setaram MicroDSC III. There are advantages and drawbacks to both sides of the dilution scale: diluted samples exhibit clear baselines at the beginning of growth, with time – extended thermograms; concentrated samples display time – compressed thermograms, the onsets of which are overlapping with the instrument equilibration (the growth starts before the instrument is ready

to effectively measure it). As detailed in Methods, a compromise between the two situations was adopted within the present study, involving samples kept in cold storage (“dormant cultures”) of approximately the same initial concentration (turbidity controlled). In-depth analysis of the influence of experimental conditions on the bacterial growth thermograms Oxygen dependence of growth The oxygen content clearly influences the thermograms of both strains in different ways, probably due to different metabolic pathways (Figure  1). For Staphylococcus aureus, higher volumes of oxygen result in www.selleckchem.com/products/Roscovitine.html extended times of growth (broadening) associated with the second peak, Fluorometholone Acetate while the effect on its height is less evident. For Escherichia coli the increase in air volume results in the increase of the height of the second peak that makes it a good predictor of the volume of available oxygen. The hermetical sealing of the microcalorimetric batch cells affords the estimation of the oxygen content influence on the growth of the

two microorganisms. Due to different growth conditions, reported shapes of the thermograms pertaining to the same strain are often different. Out of several factors that contribute to the shape of the thermogram, the following analysis is restricted to the contribution of the oxygen (air) volume. As shown in Figure  2, samples with lower volumes produce higher amounts of heat per ml suspension. The most probable cause of this thermal effect increase is due to the larger amounts of oxygen available in the microcalorimetric cell headspace and, via diffusion, to bacterial growth. Peakfit decomposition of the thermograms A natural extension of the analysis is to decompose the observed thermal signal into its components (by means of Peakfit® – Systat software) and examine their variation with (cell headspace) air volume. [The term “deconvolution” is often improperly used for various cases of complex signal analysis.