ESX1 and infection: Hence, on one hand, it is tempting to speculate that the regained robust ESX-1 functions in RD7-to-RD10-deleted MTBC strains might have created the conditions for successful infection of new mammalian hosts (animal-adapted strains) while maintaining a certain faculty to successfully infect humans (M. africanum L6 and L9 strains) (Orgeur and Brosch 2018).