You have isolated a clinical sample and carried out a gram stain on the bacteria

Question

You have isolated a clinical sample and carried out a gram stain on the bacteria in hopes to identify what is causing the illness in your patient. The gram stain showed a gram-positive staphylococcus. You have narrowed down the possible bacteria to only those used in this lab. What are the possible bacteria that you have isolated? If there is more than one possible bacteria, what test would you use to differentiate between them?

the possible bacteria used is:

Staphylococcus aureus

Staphylococcus epidermidis

Staphylococcus saprophyticus

Micrococcus luteus

Streptococcus pyogenes

Streptococcus agalacteae

Streptococcus mitis

Enterococcus feacalis

Explanation / Answer

Out of the given given organisms on Staphylococcus aureus is the only coagulase positive staphylococcus meaning it is the only organism that can produce coagulase in the given Staphylococcus sp.. So a coagulase test could be performed to differentiate it from other Staphylococcus. Catalase test could be performed to distinguish staphylococcus from Streptococcus and Enterococcus. Because S.aureus is catalase positive. Micrococcus luteus is also coagulase and catalase positive, so to distinguish it from staphylococcus aureus, bacitracin susceptibility test could be performed. M.luteus is sensitive to bacitracin, whereas S. aureus is not.

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