NTM are broadly differentiated into rapidly and slowly growing forms (<7 days and ≥7 days, respectively). M. abscessus, M. fortuitum, and M. chelonae are examples of rapid growers; species such as M. avium and M. intracellulare (the M. avium complex, or MAC), M. kansasii, M. ulcerans, and M. marinum are slow growers.