Definitions according to ISO 11133

Performance of culture medium

Response of a culture medium to challenge by test organisms under defined conditions expressed in one or more functions such as productivity, selectivity, selectivity and specificity. The incubation conditions of the media are mentioned in the corresponding analyses standard.

1. Productivity of culture medium

Level of recovery of a target microorganism from the culture medium under defined conditions

2. Selectivity of culture medium

Degree of inhibition of a non-target microorganism on or in a selective culture medium under defined conditions

3. Electivity of culture medium / Specificity of culture medium

Demonstration, under defined conditions, that non-target microorganisms do not show the same visual characteristics as the target microorganisms

Interpretations and calculations:
  • Productivity
  • The productivity PR of solid culture media calculation is:PRNS
    N0
    Ns = is the total count obtained on or in the culture medium under test
    N0 = is the total count of colonies obtained on or in the defined reference culture medium obtained from one or more plates, and shall be around 100 cfu
  • Turbidity
    For the performance of liquid media
    Turbidity is categorized as; 0 – no turbidity; 1 – slight turbidity; 2 – good turbidity
  • Growth
    For the qualitative streaking methods
    Growth is categorized as; 0 – no growth; 1 – weak growth (partial inhibition); 2 – good growth

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