Standardisation of the Microbial Inoculum

The diameter of the zone is plotted against log of concentration. This indicates the concentration of standards to use in future assays. If the microbial growth is heavy and/or zones are too small, the dilution of the inoculum and/or the concentration of the growth repressor/activator may be adjusted. Suitable parameters should be noted for future reference. 

The concentration of bacterial inoculum giving suitable results may be determined using direct microscopic count, viable counts, turbidity tubes, or spectrophotometric methods. These methods may not give the same result so one standard method should be used (see Chapter 5). Spectrophotometric methods may produce varying results between species due to differences in the size of the cells and hence their light scattering properties. Each species should therefore be checked. 

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