"what is a microorganism [a microbe] that is innocuous [not harmful] to man or to a given animal species? it is a living being which does not possess the capacity to multiply in our body or in the body of the animal. but nothing proves that if the same microorganism should chance to come into contact with some other of the thousands of animal species in the creation, it might invade it and render it sick. its virulence might increase by repeated passages through that species, and might eventually affect man or domesticated animals." —louis pasteur

what is a reasonable inference to draw from this quote by louis pasteur?