Determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) using a novel dilution tube method

A novel ‘dilution tube method’ (DTM) which is a modification of the ‘dilution method’ (DM) is hereby described for the determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). This new DTM uses only broth medium in tubes and the required antibiotic. MIC and MBC for Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus were determined in tubes by double diluting (or higher dilutions), broths containing gentamicin concentrations that inhibit bacterial growth, and incubating at 37°C for 18 to 24 h. The tube for MIC showed growth and appeared turbid after incubation while that for MBC remained clear. The results obtained using DTM agrees completely with those obtained with DM. The advantages of this novel DTM include the elimination of extra stress, time and costs associated with preparing and inoculating agar medium as done in DM.   Key words: Antibiotics, minimum inhibitory concentration, minimum bactericidal concentration, dilution tube method, dilution method.