This culture was then adjusted with 0.01 M phosphate buffered saline pH 7.4 (PBS, Lab Dr. Bichsel, Interlaken, Switzerland) to an OD600 of 0.01. Antibiotics preparation The 12 antibiotics used in this study for E. coli and S. aureus were chosen from among those listed

in the CLSI manual [15]. All antibiotics were purchased from Fluka, Buchs, Switzerland. The required concentrations were prepared in cation-adjusted Mueller-Hinton Broth (MHII, Mueller Hinton II broth, Difco) by serial dilution from a stock solution according to the CLSI manual [15]. The Results section indicates which antibiotics were evaluated with which bacteria and at what concentrations. Sample preparation for microcalorimetry Prior to use, the ampoules and the closures Lapatinib solubility dmso (rubber septa with integrated metal crimp-seal collars) were washed and separately sterilized (121°C, 20 min). They were then aseptically filled with 2.97 ml of MHII with or without added antibiotic and inoculated with 1% (30 μl) of the prepared inoculum (as described above). In addition, blanks were prepared (media alone, no inoculum) and evaluated calorimetrically to verify that measured heat flows were in all cases due only to microbial activity. Prior to inserting ampoules, the thermostat

and its calorimeters were equilibrated for at least 45 min at 37°C. The ampoules were then inserted in the calorimeters and lowered into the equilibration position. (Each of the 48 calorimeters is selleck screening library a separate instrument, and each evaluation is started, recorded and stopped separately.) At 15 min post-insertion, the ampoules were lowered down selleck compound to the measuring positions. Then, 45 min later,

after a calorimeter’s heat flow signal has regained stability, the actual measurement of the heatflow vs. time started. This time was taken as time zero for the evaluation of the data and was thus actually ~1 hour after introducing the inoculum into the medium at room temperature. Standard interpretation method Unless otherwise stated, each standard (non-calorimetric) experiment was performed in parallel with a calorimeter ampoule placed in a water bath at 37°C and evaluated after 24 h incubation using a photometer set at a wavelength of 600 nm. The sample preparation and the ampoules used for these experiments were the same as for the IMC experiments. All experiments, IMC and standard method, were performed in triplicate. Acknowledgements This work was supported mainly by Grant No. 301 from the Velux Foundation, Zurich, Switzerland. We have also received support for microorganism and other cultured cell microcalorimetry from the Department of Orthopedic Surgery, University of Basel Faculty of Medicine. Our laboratory receives general support from the Hardy & Otto Frey-Zünd Foundation, Basel, Switzerland. Finally, we are extremely grateful to PD Dr. T.