ESX1 and tuberculosis: In slow-growing pathogenic mycobacteria, like Mycobacterium tuberculosis and Mycobacterium bovis, the causative agents of tuberculosis (TB), and Mycobacterium marinum, the agent of TB in fish and amphibians and a less hazardous surrogate model often used to study TB pathogenesis, there are five paralogous type VII secretion systems, called ESX-1 to ESX-5 (1).