Also initial ΔQ/Δt values (Fig. 1B) declined with increasing antibiotic concentration, but Q max Raf inhibitor tended to a maximum value (~9 J) independent of antibiotic concentration. The calorimetric method thus highlighted differences in action of the two cephalosporines.

E. coli and penicillins. (Fig. 2). Ampicillin and piperacillin were tested as members of the penicillin family. Additionally, the monobactam aztreonam was included in this group, because it is another antibiotic interacting with cell wall this website synthesis but with a different mode of action. The grouping with ampicillin and piperacillin also facilitated a comparison of the curve profile differences. For ampicillin, the MIC could not be determined by either method with the range of concentrations used, although a decrease in heatflow could be detected for 8 mg l-1. For piperacillin, the MIC for E. coli was determined as 4 mg l-1 which corresponds to the value for quality control in the CLSI manual [15]. At the beginning of the experiment, a slight transient increase of the heatflow curve was detected at the MIC as well as on the delayed heatflow curve for a concentration of 2 mg l-1 piperacillin (Fig. 2). The MIC for aztreonam was “”on ASK inhibitor the edge”" of determination as 0.25 mg l-1 using standard methods (OD600 0.06). However, the results of IMC show that the

MIC was higher, and the tested concentrations were too low (Fig. 2). As discussed above, the concentrations of ampicillin were too low to provide much information. However, at 8 mg l-1 P max

decreased. The profiles of the heatflow curves were similar for piperacillin and aztreonam and (Fig. 2A). The heatflow curve at the highest subinhibitory concentration of aztreonam (0.25 mg l-1) had a higher t delay than the one for piperacillin (2 mg l-1) – roughly 950 min vs. 445 min. As is generally the case, antibiotics tended to lower P max . For the heat curves (Fig. 2B) the initial ΔQ/Δt values declined with increasing antibiotic concentration, but the effect was stronger for Flavopiridol (Alvocidib) aztreonam. As before, Q max values tended toward a maximum of 9–10 J not related to antibiotic concentration. E. coli and bacterial protein synthesis inhibitors. (Fig 3.) Two antibiotics inhibiting bacterial protein synthesis were evaluated, amikacin and gentamycin. For gentamycin, the MIC was determined as 1 mg l-1 which is in concordance with the reference MIC as proposed by the CLSI manual [15]. For amikacin, the MIC could not be determined with the tested concentration range by either method. For IMC, after approx. 1100 min (~18 hours) the heatflow curve of the highest concentration of 4 mg l-1 started to increase. The growth of E. coli at this concentration was also confirmed using the standard method, resulting in an OD600 of 0.2 for the samples in the calorimeter and 0.7 for the samples in the water bath.