The environment niche, This factor largely determines the development of the infection. two-component systems, which regulate virulence and resistance at the same time and which depend on external stimuli; the presence/absence of specific molecules (e.g., depletion of iron during the course of an infection in the host); the antibiotic concentration, which depends on the anatomical site of an infection; and a high NaCl concentration in the environment
Conditions will vary depending on what your working on and which virulence genes you want to induce.
When it Change the normal habitat and enter sites, so there is a need for virulence factor release. And under selection pressure of Ntibiotics, the resistance will emerge soon later.
Bacteria under stress like change its habitate from intestine to urinary system for example it express the virulence factors to protect itself, also when antibiotc used the bacteria attempt to get the gene of resistance .
If you need to express anything in the host, you bring the requirement for that expression. The antibiotic resistance will be expressed only in the presence of an antibiotic. Doesnt matter what medium or supplements you use. If you are looking for histidine competence, then you should add a minimal media without histidine. like wise you have act.
To know the working concentration of the antibiotic, You might want to look into the plasmid and identify what is the dosage it can tolerate. if you cant find it out, then i would suggest you to go with readily available strips that has gradient concentrations of antibiotics. It will show you the perfect concentration at which your host works perfectly.