You want to know if a new species of bacteria we identified (E. glados) has resistance to the antibiotic valinomycin. You make “plates” of LB-agar to culture bacteria on. Some of these are regular LB-agar plates that any bacteria will grow on and others have valinomycin in them, to prevent growth of bacteria without resistance to this antibiotic. You plate E. glados on the valinomycin-containing LB-agar plates and see that no colonies grow. In this experiment to test if E. glados is valinomycin-resistant, what is the simplest positive control you can perform?
Would it be simply if E. glados grows on media without antibioitics in it?
Or would it be growth of E.glados on media with another form of antibiotic resistance on it? I know that it is simplest, but I'm not sure if I'm missing the purpose of a positive control
What is this?
The simplest positive control you can perform in this experiment is to plate a known valinomycin-resistant bacterium, other than E. glados, on the valinomycin-containing LB-agar plates. This control will confirm that the valinomycin in the plates is active and able to inhibit the growth of susceptible bacteria. By comparing the response of the known valinomycin-resistant bacteria to E. glados, you can determine whether E. glados is resistant to valinomycin or not.
To perform this positive control, you would follow the same procedure as plating E. glados. Prepare a separate plate with valinomycin-containing LB-agar, but instead of using E. glados, use a known valinomycin-resistant organism as a positive control. If colonies grow on this control plate despite the presence of valinomycin, it confirms that the valinomycin in the media is not inhibitory to valinomycin-resistant bacteria. On the other hand, if no colonies grow on the control plate, it suggests that the valinomycin in the media is effective and supports the conclusion that E. glados is not valinomycin-resistant.