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