Dont be completely grossed out by the bacterial

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Don’t be completely grossed-out by the Bacterial Numbers on your Nutrient Agar Plates. The Chances are that most of these Bacteria are Harmless. But be Afraid -- be very Afraid -- of the Bacteria on your MacConkey Agar Plates. These are nasty Bacteria that can and will make you very sick. This is why all Hamburger should be thoroughly cooked. Let’s hope you’ve eaten your last Rare Hamburger. But don’t worry if you like Rare Steak or Rare Roast Beast. The Animal Muscle itself is close to Sterile. This is one Reason why Boxers in the 1930s and 1940s would put a Raw Steak on Eye Wounds (the other Reasons being that it was Cold and that it was readily pliable and would conform to the Shape of the Face). Nowadays, a Bag of Frozen Peas works better and costs a lot less than a Raw Steak. Your Viable Count Plates will be seriously Stinky! Figure 7-1 Morphology of Contiguous Bacterial Colonies. The first four Colonies are fairly obviously produced by two Bacteria; the fifth Colony is probably the result of three adjacent Bacteria.
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Lab 7 Page 15 Gram Positive Biochemical Tests Catalase (Atlas Page 63) “Does this Bacterium produce the Enzyme Catalase to break-down Hydrogen Peroxide?” You should already have the Results from the Catalase Tests you performed on your Gram Positive Cocci in the last Lab. • Catalase Positive (Micrococcus luteus and Staphylococcus epidermidis ) The Addition of Hydrogen Peroxide to a Goober of Bacteria on a Microscope Slide produced vigorously fizzing Wombat Spit. • Catalase Negative (Streptococcus lactis ) The Addition of Hydrogen Peroxide to a Goober of Bacteria on a Microscope Slide produced absolutely no Reaction. Remember that our Lab Strain of Staphylococcus epidermidis occasionally take up to 10 Minutes to fizz. Before you make a Catalase Negative Determination on your Biochemcal Unknown you should drop some Hydrogen Peroxide (three or four Drops) directly onto your Unknown Plate. YGC Plates “Does this Bacterium produce Pigment on YGC Medium?” “Does this Bacterium produce Acid on YGC Medium? You should already have the Results from the Catalase Positive, Gram Positive Cocci you streaked onto YGC in the last Lab. • Yellow Colonies not surrounded by a Zone of Clearing are Micrococcus luteus . • White Colonies surrounded by a Zone of Clearing are Staphylococcus epidermidis . • Ittsy-Bitsy, Teeny-Weeny Colonies so small you can barely see them but surrounded by a Zone of Clearing are Streptococcus lactis .
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Lab 7 Page 16 Gram Negative Biochemical Tests Oxidase (Atlas Page 87) “Does this Bacterium have the Enzyme Cytochrome Oxidase?” You should already have the Results from the Oxidase Tests you performed on your Gram Negative Bacteria in the last Lab.
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