To establish a link between a specific bacterium and a skin disease, researchers have shown that the bacterium was present in sick persons but not in healthy individuals. they isolated the bacterium in a pure culture and demonstrated that experimental healthy animals injected with this culture became sick. what other experiment do researchers need to perform to be absolutely sure that the bacterium is responsible for the disease? a) demonstrate that the bacterium coevolved with the diseased individual b) demonstrate that the bacterium is not able to live outside of humans or animals c) isolate bacterium from an infected sick animal and demonstrate that it is the same bacterium as the one used for infection