If you wanted to grow a large quantity of streptomycin-resistant Escherichia coli, which of the following steps would be most appropriate?

• A. Grow the bacteria on a medium without any antibiotics.
• B. Expose the bacteria to ultraviolet light to induce mutations.
• C. Add penicillin to the growth medium.
• D. Inoculate the bacteria onto a medium containing streptomycin.

Answer: (D)

Verified step by step guidance

1. Understand the goal: to grow a large quantity of streptomycin-resistant Escherichia coli, you need to select for bacteria that can survive in the presence of streptomycin.
2. Recognize that growing bacteria on a medium without antibiotics will not select for resistant strains, so both resistant and non-resistant bacteria will grow.
3. Know that exposing bacteria to ultraviolet light induces random mutations, which is not a controlled or efficient way to obtain streptomycin-resistant bacteria.
4. Adding penicillin to the medium will select for bacteria resistant to penicillin, not streptomycin, so it is not appropriate for selecting streptomycin resistance.
5. Therefore, the correct approach is to inoculate the bacteria onto a medium containing streptomycin, which will inhibit the growth of non-resistant bacteria and allow only streptomycin-resistant Escherichia coli to grow.