Respuesta :
Answer:
The culture medium must be selective
Explanation:
Selective media are the media that have those ingredients which favor the growth of a particular bacterium and inhibit the growth of unwanted bacteria. So a selective media is used to selectively grow a particular micro-organism.
For example, MacConkey agar is a selective media that is used to isolate gram-negative enteric bacteria based on lactose fermenting ability. It contains ingredients like bile salt and crystal violet which inhibits the growth of gram-positive bacteria therefore it only allows the growth of gram-negative bacteria.
Staphylococcus epidermidis is a gram-positive bacteria and E.coli is gram-negative enteric bacteria so MacConkey agar can be used to select E.coli over Staphylococcus epidermidis. So the correct answer is the culture media must be selective.
