Samples will contain Micrococcus luteus or Staphylococcus epidermidis . 2. Selection You’ll use your Loop to streak a YGC Plate from an Isolated Colony on a Patient Sample Plate. Your Plate will be incubated at 37°C for 48 Hours. After Incubation, the Plate will be examined for smooth, round Colonies which are either Yellow or Whit -to-Cream in Color. White-to-Cream Colonies surrounded by a Zone of Clearing are Staphylococcus epidermidis from your “Patient”, a Non-Pathogenic Species. A Gram Stain of Bacteria from a single Colony should reveal Gram Positive Spheres (Cocci), which may still be in Clusters. Bright Yellow Colonies that are not surrounded by a Zone of Clearing are Micrococcus luteus from your “Patient”, another Non-Pathogenic Species. A Gram Stain of Bacteria from a single Colony should reveal Gram Positive Spheres, which will not be in Clusters. White or Red Colonies that are not surrounded by a Zone of Clearing are probably a different Species of Micrococcus . They represent a Non- Pathogenic Contaminant from the Air. A Gram Stain from a single Colony should reveal Gram Positive Spheres, which will not be in Clusters Yellow Colonies surrounded by a Zone of Clearing are probably a different Species of Staphylococcus , possibly Staphylococcus aureus . They represent a Pathogenic Contaminant from your Skin. Staphylococcus epidermidis is Common and constitutes the Skin Flora of essentially all Humans. Staphylococcus aureus is somewhat less Common and -- along with Staphylococcus epidermidis -- is a Portion of the Skin Flora for approximately 25% of Humans. Staphylococcus aureus is not a potential Pathogen; it is a Pathogen. _______________________________________________________________________ Please do not streak any Plates or make any Smears from any such Colonies. _______________________________________________________________________ Please put any YGC Plates on which any such Colonies are growing into Oscar.
Lab 1 Page 31 3. Purification An Isolated Micrococcus luteus Colony (Yellow, without a Zone of Clearing) should be streaked onto YGC and incubated at 37°C for 24 Hours. An isolated Staphylococcus epidermidis Colony should be streaked onto YGC and incubated at 37°C for 48 Hours. 4. Identification Smooth, round Yellow Colonies of Gram Positive Cocci that are not surrounded by a Zone of Clearing on a YGC Plate indicate Micrococcus luteus . Smooth, round White-to-Cream Colonies of Gram Positive Cocci that are surrounded by a Zone of Clearing on a YGC Plate indicate Staphylococcus epidermidis . The Catalase Test will be used to separate Streptococcus lactis (Catalase Negative) from Micrococcus luteus and Staphylococcus epidermidis (both Catalase Positive) Biohazard Note Your Skin Isolate will be either Micrococcus luteus or Staphylococcus epidermidis . Both Species are Non-Pathogenic. It is quite likely that some Clans will “isolate” other Species of Micrococcus as a Contaminant from the Air by leaving your YGC Plate uncovered for too long while you were streaking, allowing a Piece of Dust from the Air (and Micrococcus sp. on this Piece of Dust) to settle on your YGC Plate. Double-check by holding your YGC Plate at an Angle to the
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- Winter '09
- Bacteria, Escherichia coli, plate, Agar plate, nutrient agar, Petri plates