Micro Lab Report

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Isolation and Identification of Staphylococcus aureus and epidermidis Wendy Heck
Bio 175: General Microbiology
Fall 2012-11-21

 Staphylococcus aureus is the most pathogenic for humans
and Staphylococcus epidermidis is part of the normal flora and is of low pathogenicity. Staphylococcus epidermidis and Staphylococcus aureus are two medically important species of bacteria. A culture from the nose and throat was taken to perform whether or not Staphylococcus epidermidis or Staphylococcus aureus were detected. Test were performed to determine which Stpahylococci was present and the results of the test indicated that Staphylococcus epidermidis was present.

The genus Staphylococcus includes more than 20 species as described in Bergey's Manual (2001). Only two are significant to humans, Staphylococcus aureus and Staphylococcus epidermidis. S. aureus colonizes mainly the nasal passages, but it may be found regularly in the oral cavity, gastrointestinal tract and the skin. Staphylococcus epidermidis is an inhabitant of the skin. Of these two Staphylococcus aureus is serious pathogen. Staphylococcus epidermidis is of the normal flora and is not considered to be a serious pathogen (textbookofbacteriology.net). Staphylococcus epidemidis becomes pathogenic when the skin is broken or through contamination from medical procedure. Staphylococcus aureus are only able to invade via broken skin or mucous membranes. Staphylococcus aureus is very heat resistant and reheating foods will not destroy it, although the bacteria may be destroyed (www.sunysccc.edu). About 30 per cent of healthy humans are carriers of S. aureus, they have the bacteria on their skin without any active infection or disease. Staphylococci hide their antigens to avoid an immune response many different ways to include killing infection-fighting cells (phagocytes), surviving within host infection-fighting cells, and developing a resistance to antibiotics (www. dermnetnz.org)

Purpose & Results:
Genus Tests
I. Gram Stain:
a. The purpose of the Gram stain is to confirm that the isolate(s) have the physical characteristics of Staphylococci. b. If the isolate is a Staphylococci it will be a Gram positive cocci, which will be purple in color and rod shaped, arranged in clusters. c. After performing the Gram stain on the isolates from the quadrant streak, the isolate were found to be Gram positive, which is positive for Staphylococci.




d. A smear was created from a pure culture of Staphylococcus. It was chosen from the throat one DNA agar. The isolate was gram stained and viewed under oil immersion. The cocci were purple, which indicates a gram positive. Staphylococci divide in various directions forming grape-like clusters, single cocci, or just a few together.

II. Catalase-explain why it bubbles
e. The purpose is to confirm weather strep or staph
f. After putting a drop of peroxide onto isolate it is expected to bubble. g. After applying the peroxide to isolate it did bubble up to indicate Staphylococci. Species Tests
III. Mannitol Fermentation:
h. The purpose-To grow and isolate colonies from nose and throat and differentiate between the two specie. This is done by prefoming a quadrant streak on a mannitole salt augur medium to isolate bacteria from the nose and throat and identify as Staphylococcus aureus or Stahyloccus epidermidis i. Expected results-To have isolated colonies surrouned by yellow which is indicative of mannitol fermentation. Staphylococcus aureus mannitol fermentation produce acid results in the media tuning it yellow. There is no fermentation in Staphylococcus epidermidis, so media does not change, the medium remains red. j. Your results-No mannitol positive colonies were present, therefore no mannitol fermentation developed. If positive colonies were present there would have been a...
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