(a) The sample containing the microbes (e.g. soil) is put in a nutritive medium and allowed to grow in shake cultures.
The growth conditions (e.g. temperature, nutrients) in the medium are provided and these favour the growth of microbes of our interest.
(b) Screening is done using a method where the organism will show its desired properties.
For example, if we are looking for a microorganism, which produces an antibiotic, we may detect it by growing the culture on an agar plate in the presence of that bacterium against which antimicrobial activity is desired.
Immunological methods are also available in which the microbes producing products are detected using specific antibodies.
Use of probes, which enable the detection of organisms capable of producing specific products.