Recent research suggests that bacterial fitness might play a
pivotal role in the spread of antibiotic-resistant M.tb. In vitro,
bacterial fitness is determined by the interplay of numerous factors
including the growth deficits incurred by resistance mutations,
strain genetic background, and compensatory evolution. Future
studies should elucidate the interactions and relative importance
of these and other factors in the transmissibility of drug-resistant
TB. The development of new tools, such as mathematical