Francisella tularensis is a pathogenic species of Gram-negative, rod-shaped coccobacillus, an aerobe bacterium. It is non-spore forming, non-motile and the causative agent of tularemia, the pneumonic form of which is often lethal without treatment. It is a fastidious, facultative intracellular bacterium which requires cysteine for growth. Due to its low infectious dose, ease of spread by aerosol, and high virulence, F. tularensis is classified as a Tier 1 Select Agent by the U.S. government, along with other potential agents of bioterrorism such as Yersinia pestis, Bacillus anthracis and Ebola virus.