3A) t delay increased with increasing concentration, and P max decreased. For heat (Fig. 3B), there was virtually no effect on ΔQ/Δt. As before, Q max tended to a value of 9–10 Protein Tyrosine Kinase inhibitor J independent of whether an antibiotic was present. The calorimetric data thus suggest the modes of action of amikacin and gentamycin on E. coli are essentially the same. MICs for S. aureus ATCC29213 For
S. aureus we determined the MICs of 10 of the 12 antibiotics using IMC. However, for the sake of brevity and to illustrate the main findings, we only present 6 antibiotics which have the same modes of action as those presented for E. coli. The tests were also performed in parallel in a water bath and evaluated using the standard visual turbidity method. Again, unless otherwise stated,
the results of both methods were in agreement with each other. S. aureus and cell wall synthesis inhibitors. (Fig. 4) The antibiotics evaluated were cefoxitin and vancomycin. For cefoxitin, the MIC was determined as 4 mg l-1 whereas vancomycin had a MIC of 1 mg l-1. Both values were in agreement with the reference MIC in the CLSI manual . For both antibiotics, the t delay values for the heatflow curves (Fig. 4A) increased with increasing concentration, but the effect was stronger for cefoxitin. Also P max was reduced at the highest concentration not inhibiting growth. For the heat curves (Fig. 4B) there was little change in ΔQ/Δt with antibiotic concentration. However Q max declined, but as shown, the highest value observed was ~5 J. This is far below the maximum value of 9–10 J seen repeatedly Gefitinib for E. coli, independent of antibiotic concentration, and differences here can be attributed to differences
in t delay . Thus the chief difference shown by IMC was the stronger effect of RANTES cefoxitin on initial bacterial activity. S. aureus and protein synthesis inhibitors. (Fig. 5) The MICs were determined as 16 mg l-1, 0.5 mg l-1 and 0.25 mg l-1 for chloramphenicol, erythromycin and tetracycline, respectively, which are identical to the values in the CLSI manual . The overall profiles of the subinhibitory heatflow curves (Fig. 5, column A) and heat curves (Fig. 5, column B) were remarkably similar for all three antibiotics. None of the three antibiotics produced a substantial increase in t delay . The only substantial difference was for the maximum heatflow rate, P max . Tetracycline had a much larger influence on P max than the other two antibiotics. All three antibiotics produced a decline in ΔQ/Δt with increasing concentration. Changes in Q max with concentration can be attributed to the differences in ΔQ/Δt. The IMC data suggest that all three antibiotics affect the rate of bacterial growth but do not delay its onset. S. aureus and an antibiotic acting on DNA. (Fig. 6) Only one antibiotic was tested which interacts with bacterial DNA, namely ciprofloxacin. The MIC was determined as 0.5 mg l-1 using IMC which corresponds to the reference value in the CLSI manual .