3.A group of researchers have isolated a new bacterium, bacterium X, from the lymph nodes of several patients who returned from a camping trip and presented in the emergency room with high fever, rash, and swollen lymph nodes. Based on a 16S rRNA sequence comparison, they determined that this new bacterium is distantly related to the gram-negative bacterium Francisella tularensis. The researchers developed a tissue culture model of invasion using a phagocytic cell line and a mouse model of infection (via injection). They found that bacterium X binds to and invades phagocytic cells. Using a mouse model of infection, the researchers isolated two avirulent mutants of X that they call Xmut1 and Xmut2, both of which grew as well as the wild type in vitro. In the tissue culture model of invasion, Xmut2 could still bind to and invade the phagocytic cells just as well as wildtype W, while Xmut1 could not. To confirm that the genes disrupted in the two mutants indeed encoded proteins important for virulence, the researchers compared the mutants to wild-type (wt) bacterium X in the mouse model of infection. The results are summarized in the table below: Strain Dose (CFU) Day 3 Mortality (Dead/Total Number) Day 7 Mortality (Dead/Total Number) CFU obtained on Day 3 from Lymph Node of Mouse Wt 10 2/10 10/10 103 Wt 102 3/10 10/10 105 Wt 103 6/10 10/10 106 Wt 104 9/10 10/10 108 Xmut1 106 0/10 0/10 0 Xmut 1 107 0/10 0/10 10 Xmut 1 108 0/10 0/10 103 Xmut 2 108 0/10 0/10 102 Xmut 2 1013 0/10 1/10 108 Xmut 2 1016 1/10 3/10 1017 Now find out the infectious dose & LD50 value for each of the wild type and mutant strains. Interpret your result.