Complex sentence: It only took one to 10 cells of "F. tularensis" to kill the animal of either species, although "F. novicida" took 10 to 100 cells in cavies and up to a 1,000 cells in mice.
Split into simpler sentences: It only took 1 to 10 cells of "F. tularensis" to kill the animal of either species. On the other hand, "F. novicida" took 10 to 100 cells in cavies and up to a 1,000 cells in mice.