Staphylococcus Aureus

A streak culture was performed on a Tryptic Soy Agar Plate for isolation and purity and then incubated at 37 degrees Celsius for 24 hours.

A gram stain was performed to determine whether the bacterium was a gram negative or a gram positive. After performing the gram stain, I concluded that by the appearance of purple spherical clusters resembling grapes that is was a gram positive cocci.

A Catalase test was then performed using hydrogen peroxide. A positive catalase test was observed when bubbles started to form on the culture distinguishing Staphylococcus spp. form on the culture distinguishing Staphylococcus spp. from Streptococcus spp.

Finally, a Mannitol Salt Agar was streaked and incubated at 37 degrees Celsius for 24 hours to determine whether the bacteria was Staphyloccus aureus or Staphylococcus epidermidis. A positive conformation of Staphylococcus aureus is the ability of the bacteria to ferment the carbohydrate mannitol which produces yellow growth when mannitol is b roke down to lactic acid.

After 24 hours, the bacteria colonized and yielded a yellow growth validating that it was unquestionably Staphylococcus aureus.

Staphylococcus aureus is a gram positive bacterium with a pherical morphology. It is a faculatative anaerobe which means it will grow by aerobic respiration or fermentation that yields lactic acid. The catalase test is important in distinguishing Streptococci (catalse negavitve) from Stphylococci which are hearty catalase-producers. The test is performed by adding 3% hydrogen peroxide to a colony on an agar plate or slant. Catalase positive cultures produce oxygen and instantly bubble. The test should not be executed on blood agar because, blood contains catalase.