<Ul> <Li> a semi-quantitative way based on diffusion (Kirby - Bauer method); small discs containing different antibiotics, or impregnated paper discs, are dropped in different zones of the culture on an agar plate, which is a nutrient - rich environment in which bacteria can grow . The antibiotic will diffuse in the area surrounding each tablet, and a disc of bacterial lysis will become visible . Since the concentration of the antibiotic was the highest at the centre, and the lowest at the edge of this zone, the diameter is suggestive for the Minimum Inhibitory Concentration, or MIC, (conversion of the diameter in millimeter to the MIC, in μg / ml, is based on known linear regression curves). </Li> <Li> a quantitative way based on dilution: a dilution series of antibiotics is established (this is a series of reaction vials with progressively lower concentrations of antibiotic substance). The last vial in which no bacteria grow contains the antibiotic at the Minimal Inhibiting Concentration . </Li> </Ul> <Li> a semi-quantitative way based on diffusion (Kirby - Bauer method); small discs containing different antibiotics, or impregnated paper discs, are dropped in different zones of the culture on an agar plate, which is a nutrient - rich environment in which bacteria can grow . The antibiotic will diffuse in the area surrounding each tablet, and a disc of bacterial lysis will become visible . Since the concentration of the antibiotic was the highest at the centre, and the lowest at the edge of this zone, the diameter is suggestive for the Minimum Inhibitory Concentration, or MIC, (conversion of the diameter in millimeter to the MIC, in μg / ml, is based on known linear regression curves). </Li> <Li> a quantitative way based on dilution: a dilution series of antibiotics is established (this is a series of reaction vials with progressively lower concentrations of antibiotic substance). The last vial in which no bacteria grow contains the antibiotic at the Minimal Inhibiting Concentration . </Li> <P> Once the MIC is calculated, it can be compared to known values for a given bacterium and antibiotic: e.g. a MIC> 0, 06 μg / ml may be interpreted as a penicillin - resistant Streptococcus pneumoniae . Such information may be useful to the clinician, who can change the empirical treatment, to a more custom - tailored treatment that is directed only at the causative bacterium . </P>

The best medium for using antibiotic susceptibility testing is