Minimal selective concentration (MSC)

The minimum concentration of antimicrobial agent at which resistant strains have a competitive advantage.

At the MSC, the benefit of bacterial growth exceeds the fitness cost of carrying the drug-resistance trait compared with a non-resistant strain. At concentrations greater than the MSC, there is a competitive advantage for having the resistance trait. The difference in fitness between susceptible and resistant organisms at sub-MIC values could be much lower than the MIC against some antibiotics.

Selection of resistant bacteria at very low antibiotic concentrations (Plos Pathogens, 2011)

Selection and evolution of resistance to antimicrobial drugs (IUBMB Life, 2014)

Evolution of antibiotic resistance at low antibiotic concentrations including selection below the minimal selective concentration (Communications Biology, 2020)