t. Erythromycin 0.5 0.5 638 27 Tetracycline 0.25 0.25 330 27 Ciprofloxacin 0.5 0.5 1097 17 (almost o. t.) t delay and P max show the values of the curves determined at one concentration below the MIC value. a n. d.: not determinable using the tested concentrations. b o. t.: Outside measuring time. MICs for E. coli ATCC25922 We evaluated the MICs of 12
different antibiotics for E. coli. For brevity, we present here the results for 7 antibiotics grouped by mode of action. The antibiotics used and their concentrations can be found in the corresponding LY411575 in vitro figures. All evaluations were also performed in parallel using the standard method – visual detection of turbidity at 24 hours. Unless otherwise stated, the results for the MIC determination were the same for this website calorimetry and the standard visual method. In Figs. 1, 2, 3, 4, 5 and 6, Column A shows the recorded heat flow rate data (μW = μJ/s vs. time in min.). Any time delay (t delay ) before a heat signal was recorded was the time required until there Torin 2 were sufficient numbers of active bacteria to produce a heat flow signal above the instrument’s detection limit. The highest peak in a μW vs. time curve indicates the maximum rate of heat production observed (P max ). Column B presents the results of integrating the data in Column A to show the cumulative amount of heat produced over time (J vs. time in min.).
As explained later, the Column B curves are somewhat analogous to conventional growth curves showing the increase in the number of bacteria over time. Mean slopes (ΔQ/Δt) for a given portion of an aggregate heat curve are aggregate rates of heat production and indicative of their rate of bacterial growth. Maximum values (Q max ) are related to the total numbers of cells produced by
time t. E. coli and cephalosporines of the 1st and 2nd generation. (Fig. 1). The 1st generation cephalosporine used in this study was cefazolin and its MIC for E. coli was correctly determined using IMC as 2 mg l-1 based on the recommendations of the CLSI . At the MIC and higher concentrations there was essentially no growth. However, there was a slight temporary increase in heatflow at the beginning of the experiments. This suggests a slight transitory increase in metabolic activity of the bacteria present, followed by no subsequent growth. At all subinhibitory concentrations, Etofibrate heat production of E. coli was the same (same t delay , P max , ΔQ/Δt, and Q max ). Cefoxitin was used as an antibiotic representing the 2nd generation of cephalosporines although it is a member of a subgroup of this generation and also active for anaerobic bacteria. The cefoxitin MIC could also be determined correctly using IMC as 8 mg l-1. In contrast to cefazolin, there was no transient initial increase in heatflow at the MIC (Fig. 1A). Also, the profiles of the curves at subinhibitory concentrations differed markedly between cefazolin and cefoxitin (Fig. 1). For cefoxitin, t delay (Fig.