To establish a link between a specific bacterium and skin disease, researchers have shown that a bacterium was present in sick persons but not in...

To establish a link between a specific bacterium and skin disease, researchers have shown that a 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?