Introduction: A group of researchers at the USDA isolated a new bacterium from lungs andlymph nodes of several young horses that became ill and died at a local stable Prior to death their tymptoms induded disorientation and loss of motor function, so the researchers saspected eentral nervous system involvement, which was confirmed by the observation of brain lesions in the dead animals. Based on 16 S . rRNA comparison, the bacterium was distantly related to N . mentingitidas, and they subsequently named it Neiseria equinitie. Part A: The researchers developed a honse model of infection. During their studies, thry isolated two avirulent mutants (NeMutl and NeMut2) that were stall able to grow as well as wild-type N. erwiniar in vitro, but were less virulent in vivo. They also found that these mutants had deletions in genes eneoding putative virulence factors. To confirm that the disnupted genes in the two matants indeed encoded proteins important for vinulence, the rosearchens contpared the mutants to wild-type (Wo bacteria in the horse model of infection. The results are summarized in the table that follows: 1. Determine the LD Ds 5 and ID 10 values for each of the wild-type and mutant strains. NOTEt For this experiment, the researchers defined the IDs as the dose required to establish at least a 4 -log increase in CFU in the lymph nodes at day 3 compared to the initial CFU dose. 2. Interpret your results obtained in Question 1 above. 3. Is the L.DsuIDse a valid model to use in this particular study? Why or why not? 4. If the LDss and/or IDso values of a Wt and mutant strain are similar in this type of experiment, does this automatically mean that the mutation does not affect a virulence factor? Why or why not? Part B. The researchers decided to determine the Cl of each of the mutants, again using the horse infection model. The results are summarized in the table below: 5. Determine the Cl for NeMut1:Wt and NeMut2:Wt. 6. Interpret your results from question 5 above..

1. Introduction: A group of researchers at the USDA isolated a new bacterium from lungs
andlymph nodes of several young horses that became ill and died at a local stable Prior to death
their tymptoms induded disorientation and loss of motor function, so the researchers saspected
eentral nervous system involvement, which was confirmed by the observation of brain lesions in
the dead animals. Based on 16 S . rRNA comparison, the bacterium was distantly related to N .
mentingitidas, and they subsequently named it Neiseria equinitie. Part A: The researchers
developed a honse model of infection. During their studies, thry isolated two avirulent mutants
(NeMutl and NeMut2) that were stall able to grow as well as wild-type N. erwiniar in vitro, but
were less virulent in vivo. They also found that these mutants had deletions in genes eneoding
putative virulence factors. To confirm that the disnupted genes in the two matants indeed
encoded proteins important for vinulence, the rosearchens contpared the mutants to wild-type
(Wo bacteria in the horse model of infection. The results are summarized in the table that
follows: 1. Determine the LD Ds 5 and ID 10 values for each of the wild-type and mutant strains.
NOTEt For this experiment, the researchers defined the IDs as the dose required to establish at
least a 4 -log increase in CFU in the lymph nodes at day 3 compared to the initial CFU dose. 2.
Interpret your results obtained in Question 1 above. 3. Is the L.DsuIDse a valid model to use in
this particular study? Why or why not? 4. If the LDss and/or IDso values of a Wt and mutant
strain are similar in this type of experiment, does this automatically mean that the mutation does
not affect a virulence factor? Why or why not? Part B. The researchers decided to determine the
Cl of each of the mutants, again using the horse infection model. The results are summarized in
the table below: 5. Determine the Cl for NeMut1:Wt and NeMut2:Wt. 6. Interpret your results
from question 5 above.