ETV5 and infection: While macrolides are the backbone in the treatment of most NTM infections, current treatment guidelines by the American Thoracic Society/Infectious Diseases Society of America recommend caution in their use when treating infections by the M. fortuitum group, given the potential for development of resistance through an inducible erythromycin methylase erm gene.10 Testing for this erm gene-related resistance requires incubation of the mycobacterial isolate in the presence of a macrolide for 14 days before the assessment of its minimum inhibitory concentration.