The value of 0.05 mW was chosen for the exponential growth (“t0.05” is the time needed to reach this heat flow value) as this value lies within the time period of fully established exponential growth regime for both strains. It corresponds to the thermal activity of 2-5 × 107 bacteria. Figure 3 Graphical representation of the proposed 5 points of interest that could

be utilized as see more thermal growth characteristics of the two strains. The parameters and nomenclature proposed for the statistical evaluation of bacterial thermal growth. Table 1 Proposed bacterial microcalorimetric growth parameters for characterizing a raw thermogram Parameter Description t0.015 (h) Time to 0.015 mW heat flow, i.e. thermal growth onset time t0.05 (h) Time to

0.05 mW heat flow, i.e. established exponential growth time t1stMax (h) Time to 1st maximum heat flow, i.e. check details time to first peak t2ndMax (h) Time to 2nd maximum heat flow, i.e. time to second peak Δt0.015 (h) Time between thermal growth onset and offset HFMax1 (mW) First maximum heat flow, i.e. first peak amplitude HFMax2 (mW) Second maximum heat flow, i.e. second peak amplitude Data analysis on raw (non-normalized) thermograms All thermograms were processed as previously described [7, 16, 17] with baseline and time correction, thus eliminating the initial thermal perturbations and adjusting all experiments to a zero time reference. The baseline was calculated and subsequently subtracted using either Calisto software v1.077 (AKTS) and/or Peakfit v4.12 (SYSTAT). Zero time correction was done in Peakfit using data exported in Excel from Calisto; the final plots were done using the OriginLab Origin v. 8.1 and the Microsoft Excel software. For the statistical analysis we used SPSS 16.0 software

(SPSS, Inc, Chicago, Illinois). Data from 18 runs performed on E. coli and 8 on S. aureus with sample sizes of different volumes were analyzed, as shown in Figure  1. One may easily notice significant qualitative differences between the 2 strains. The Shapiro-Wilk [18] validity test performed on the 2 sets of data indicated a normal distribution for all parameters of E. coli and for 4 out of 7 of S. aureus thermal growth (t0.015, t0.05, Abiraterone nmr Δt0.015, HFMax1). Results are expressed as mean and standard deviation for normally distributed continuous variables (further analyzed by Student t test), or median and minimum/maximum for non-normally distributed variables (analyzed by Mann–Whitney U test). Hypothesis testing was 2-tailed, with P < 0.05 considered statistically significant. The statistical independent t-test [19] (CI = 95%, α = 0.05) and the Mann–Whitney U test performed on the 7 parameters proved that there is a statistically significant difference (with a p value < 0.0001) between the two strains (Table  2).