Answer: Rickettsia rickettsii ID50 = 1
Explanation:
Virulence is the pathogen's ability to cause infection or harm to the host. ID50 is the Infection Dose or the number of organisms required to cause infection on 50% of normal adult humans. A lower ID50 means that the pathogen has a higher virulence.
In this particular case, Rickettsia rickettsii would be the most virulent organism