Question

What are the next steps once you have an isolated colony to determine the bacteria growing in that colony? (These are some of the I’s – selective media what might you suggest?)

Answer 1

Once you have isolated colony, the next step to determine if the bacteria is growing in that colony is to use specialized media.

Many special-purpose media are available to the microbiologist to aid in the isolation and identification of specific microorganisms. These special purpose media fall into four groups: selective media, differential media, enrichment media, and combination selective and differential media.

1. Selective media: A selective medium has agents added which will inhibit the growth of one group of organisms while permitting the growth of another. For example, Columbia CNA agar has the antibiotics colistin and nalidixic acid added which inhibit the growth of Gram-negative bacteria but not the growth of Gram-positives.

2. Differential media: A differential medium contains additives that cause an observable color change in the medium when a particular chemical reaction occurs. They are useful in differentiating bacteria according to some biochemical characteristic.

3. Enrichment media: An enrichment medium contains additives that enhance the growth of certain organisms. This is useful when the organism you wish to culture is present in relatively small numbers compared to the other organisms growing in the mixture.

4. Combination selective and differential media: A combination selective and differential medium permits the growth of one group of organisms while inhibiting the growth of another. In addition, it differentiates those organisms that grow based on whether they can carry out particular chemical reactions.

PS- A positive rating would be highly appreciated

Thanks