Getting ready to do the experiment

To isolate a resistant strain, pick an isolated colony that grows furthest 'up the gradient', that is, in the presence of a high concentration of antibioltic.

Now grow up a culture of the strain check to insure that it is in fact resistant to the appropriate antibiotic and sensitive to the other.

The reason we isolated these two antibiotic resistant strains was to use antibiotic resistance to follow their progeny in a long term cultures.

Since we are looking for competition between populations, it is important to know that there is no obvious growth effect that results simply from the NalR and StrR mutations.

If there is a growth difference, we will have to go back and select a new resistant strain.