The World Health Organization (WHO) estimates that 9.6 million became ill with TB in 2014. Among this group, approximately 480,000 persons became ill with multidrug-resistant TB (MDR TB), which is TB caused by bacteria that are resistant to at least isoniazid and rifampin, the two most potent TB drugs used to treat persons with TB disease. Extensively drug resistant (XDR) strains of TB were reported by 105 countries in 2015. As such, the National Strategy for Combatting Antibiotic Resistant Bacteria (CARB) has designated Mtb a SERIOUS threat level pathogen.