At present, foodborne diseases continue to have a high impact on Public Health, not only due to the pathogenicity of their agents, but also because of their ability to become resistant to antimicrobials, such as antibiotics, biocides, essential oils, and food preservatives. It has been shown, especially with antibiotics, that prolonged exposure to them can lead to the generation of resistant bacteria. At research level, adaptive laboratory evolution (ALE) assays and genetic editing favor the isolation of resistant bacterial populations to the antimicrobials used as stressors. Moreover, prolonged exposure can occur in natural conditions and sampling techniques in the food industry can allow the isolation, if any, of RVs. The next step is to evaluate the resistance of these evolved bacterial populations against the antimicrobial to proceed to the isolation of resistant variants (RVs) for further study or characterization. However, as it is not possible to assess the resistance of all the different strains, some methodologies should be sought as screening methods. Therefore, this chapter aims to describe a screening methodology for the isolation and selection of RVs from a heterogeneous bacterial population, both in liquid and solid media, based on growth fitness assessment in the presence of antimicrobial. The first method, known as turbidimetry, consists of randomly isolating colonies from a population and selecting RVs by comparing their growth fitness in the presence of the antimicrobial on liquid medium. Meanwhile, the second method, known as “ScanLag”, compares the growth fitness in solid medium with the antimicrobial added.