Lab Exercise 14 PDF

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Lab Report 15 Name: __Michele Glantz__ Date: ___5/22/19_______

Mannitol Salt Agar Your Results and Observations Draw your results or photograph them with a digital camera or mobile device.

Interpretation and Questions Organism

Growth (1/2)

Streptococcus aureus

non-pathogenic Staph

Streptococcus epidermis

pathogenic

Escherichia coli

No growth

Sample M

non-pathogenic

Appearance of the growth or the agar around the growth Fermenting mannitol, producing acid, and changing color of pH indicator Growing but not fermenting mannitol and not producing acid Lack of growth due to inhibition by the high level of salt in medium Reflected Streptococcus aureus

Lab Report 15 1. Based on the results seen on your plate, does Sample M contain Streptococcus aureus? Why or why not? Yes, the sample results are completely identical.

2. Take a look at the Background section. Would this medium still work (be selective for S. aureus) if it did not have salt in it? Why or why not? No, the high concentration of sodium makes the medium selective by inhibiting the growth of most bacteria and allowing staphylococcus aureus to grow. 3. Your partner makes a very, very long streak in each quadrant. The inverted plates are placed in the incubator on Thursday. In class the next Tuesday, you remove your plate and the entire plate is yellow, even though there is growth in only two of the quadrants (Sample M, S. aureus) on opposite sides of the plate. How do you explain the color change across the entire plate? The very long streaks of S. aureus contaminated all of the quadrants, causing the yellow color change....