Question

Gram Stain Negative Positive Serratia marcescens Escherichia coll Bocilus subtilis Neg Lactose Fermentation Pos Lactose Fermentation Neg Lactose Fermentation Pos Lactose Fermentation Serratia marcescens Escherichiacoli Bocillus subtills Staphylococcus epidermidis Based on the dichotomous key given above, and results of the experiments you have done throughout the course, answer the following case studies. Case Study 1: Justin was spending the summer with his father on their ranch in Wyoming. One day, as they were clearing brush and branches from a deserted barn, Justin was struck in the eye with a tree branch. Part of the tree branch penetrated Justin's eye. The eye continued to worsen over the next few days and Justin's father took him to the emergency room. A culture was performed with the results shown below. Based on the dichotomous tree, what organism has infected Justin's eye Gram positive rods: Lactose fermentation negative:

Answer 1

Bases on the dichotomous tree, the organism responsible for Justin's eye infection is Bacillus subtilis . Because the result of the culture test show gram positive rods . If we see the dichotomous tree above, gram positive stains are shown by either Staphylococcus epidermidis or Bacillus subtilis. So ,organism involved can be any one among these two.

Next test indicates that organism is lactose fermentation negative. If we again see the dichotomous tree Staphylococcus epidermidis gives lactose fermentation test positive. So, this organism cannot be involved . Bacillus subtilis gives lactose fermentation test negative.So this organism is responsible for Justin's eye infection. Hence based on the results of test and dichomotous tree above the organism responsible for justin's eye infection is Bacillus subtilis, because it is the only organism in dichomotous tree above that is gram positive and lactose fermentation negative.

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