This reflects the hypothetical situation of a calorimetric cell completely filled with bacterial suspension: in this case the
whole thermal growth is given only by dissolved oxygen, i.e. by peak 1. Fairly close to the above values are the intercepts of the exponentially fitted specific values “Total heat, J/g” and “hvl-peak1, J/ml suspension”. (S. aureus values are more scattered, reflecting the scatter of the pertaining raw thermograms). This is the expected behavior for a 1 ml nominal volume of the cell: for a completely filled cell absolute (J) and https://www.selleckchem.com/products/Belinostat.html specific (J/ml) values of the thermal effect are supposed to coincide. The results presented in Figures 4, 5, 6 and 7 consistently support the idea that complex thermal growth patterns as the ones obtained in the present contribution are mainly due to the interplay between dissolved and diffused oxygen. Truly fermentative growth is not excluded, but its thermal contribution seems to be of minor importance within the growth conditions utilized. The most probable metabolic pathway accounting for bacterial growth of E. coli in batch Hastelloy cells is an aerobic one, with dissolved and diffused oxygen
acting as a growth limiting factor and resulting in the two-peak thermal growth thermograms. Epigenetics Compound Library screening Long term refrigeration viability counts check As the two MicroDSC instruments utilized in the present study are single-channel, they can run one sample at a time. Microcalorimetry is very sensitive in detecting small variations in the bacterial density of the inoculum: this is Resminostat fairly similar to the situation encountered in a busy clinical microbiology laboratory,
where each new strain would require rapid processing and analysis. Under such circumstances, even the small variability that takes place in-between experiments needs to be assessed. A series of experiments was performed to evaluate the effect of refrigeration and long-term storage on the CFU viability count, as described in Methods section. Results are shown in Figure 8 where one may notice a fairly linear decline in CFU count with the time spent in cold storage. Some cells die during cold storage and this lowers the initial concentration of the sealed samples, resulting in longer growth time lags. Figure 8 Variation of viable counts (VC) with the time spent in cold storage. The linear fit of the slight decrease of colony forming units (CFU) within 1 – 5 days spent in cold storage (4°C). VC pertain to samples stored in batch cells as detailed in Methods section. Discrimination of bacteria based on local versus overall thermogram features A most interesting approach to bacterial growth discrimination based on the thermal microcalorimetric signature was advanced by Bermúdez, López et al. more than 25 years ago [26, 27].