Resistance is caused by newly acquired genetic traits (by mutation or horizontal gene transfer) that are heritable and confer the ability to grow at elevated concentrations of antibiotics. In contrast, tolerant bacteria have the same minimum inhibitory concentration (MIC) as susceptible bacteria,[4] and differ in the duration of the treatment that they can survive. Antibiotic tolerance can be caused by a reversible physiological state in a small subpopulation of genetically identical cells,[2][7][10] similar to a differentiated cell type.[13] It enables this small subpopulation of bacteria to survive their complete elimination by antibiotic use.