I am evaluating an organic extract of Aspergillus on Staphylococcus aureus using a 6 mm disc in agar Muller Hinton.
I am want to determine a breaking point, is it enough to say that a halo of inhibition greater than 6 mm shows antimicrobial activity?
How can I base this hypothesis?
A halo >6 mm means that you have antimicrobial activity of your extract (or the solvent!) versus the Staph. aureus. A breakpoint, however, is a zone inhibition diameter (halo), which allows a prediction of therapeutic success. In other words, a breakpoint is not what you are looking for.
Rather, you may compare the antimicrobial activity of the extract against other (well characterized/commercial) compounds or antibiotics. For this you should go with another assay (i.e. microdilution) which allows comparing antimicrobial activity on a quantitative scale. Again, a microdilution based (MIC) breakpoint is a measurement to predict therapeutic success, and therefore nothing to determine early in a project.
Make sure to include pure solvent as a control in all of your assays to rule out inhibition by the solvent.
Dear Sanchez,
First of all, may i ask you if you apply an international standard isolate like American Type culture Collection (ATCC). It is so important to check all daily experiment variables. Also, the zone diameter for any disk is 6 mm. more than this is considered starting of inhibition. The international organization of susceptibility pattern like WHO and etc classified the zone to resistance , intermediate and sensitive according to the zone of inhibitions and for each bacterium there is a pre-known disk potency and suggested zone of inhibitions for the above three criteria. Best regard
Hello
If you have the antibiotics you can determine the break points of them by CLSI guidelines but here you have new material ,you can compare the inhibition zone of this material with antimicrobial activity of control antibiotics used to treat this bacteria.
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