Dichotomus key gram postive bacteria coccus - Lab Report Example

We first confirm that the unidentified bacterial species is a gram-positive one, or it has a thick peptidoglycan layer that absorbs the crystal violet stain during the gram staining test. This is because unlike other common bacteria such as Eschericia, Pseudomonas, Shigella and Salmonella, Staphylococcus and Micrococcus bacteria are gram-positive. It is also during this initial test that we can also check the shape of the bacteria being identified. We know that Staphylococcus and Micrococcus are circular in shape, unlike the gram-(+) Bacilli that is more elongated and rod-like in shape.

However, so is the gram-(+) Streptococcus and Enterococcus. In fact, they are collectively known as the gram-(+) cocci. Thus, to differentiate them, we use the catalase test, which determines whether an organism is able to convert the toxic hydrogen peroxide into water and oxygen. Of the four main gram-(+) cocci genera, only Staphylococcus and Micrococcus are catalase-(+). We then try to grow it on Mannitol Salt Agar. The genus of Micrococcus is unable to use mannitol for food, and thus will not grow on MSA medium.

On the other hand, Staphylococcus is able to grow on MSA because they can oxidize mannitol. Finally, we try to determine whether the unknown is S. aureus or S. epidermidis by growing it on blood agar. Since it did not cause hemolysis, then the organism is S. epidermidis, because S. aureus is a known alpha-hemolytic organism. http://www.mesacc.edu/~aleid84161/personalhomepage/Flow%20Charts.pdf, n. d.). References(n.d.) Gram positive cocci. Retrieved from: http://www.mesacc.edu/~aleid84161/personalhomepage/Flow%20Charts.pdf