You go to perform a Gram stain on a patient's bacterial culture that is suspected to contain S. aureus. You notice that the cultures have been incubated for 48 hours instead of the normal 24 hours. When you examine the stained slides, you see a lot of color variability, ranging from an intense blue/purple to shades of pink. Explain how this result could occur and what likely caused it. You obtain a fresh sample from your patient and incubate it for 24 hours. You perform the Gram stain again and see the grape-like clusters that are consistent with Staphylococcus aureus (as you expected); however, all of the cells are red/pink instead of purple (S. aureus is a Gram-positive organism). You run additional tests and confirm that the patient's sample does contain S. aureus. Explain how this Gram stain result could occur and what likely went wrong in the Gram stain process.
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A student divides a slide in half and places a mixed culture smear of E. coli and S. epidermidis on one side and a pure culture smear of an unknown microbe on the other. They Gram stain the slide and begin their observations by looking at the mixed smear under oil immersion. Evaluate the student's Gram staining technique when the following results are observed. Explain what the student may have done wrong. If they also observe the unknown smear on the same slide, are their results likely to be accurate? Both the rods and the cocci appear purple. You can only find rods and they are all pink. What is wrong with putting an unknown organism and the control mixed culture smear on different slides? Why would a healthcare provider be interested in knowing the Gram reaction of a pathogenic bacterium?
Sri K.
1. Match the expected result (purple, red, or colorless) to the following descriptions of Gram-stained cells. Consult your chart at the beginning of this lab report if you need help remembering the correct Gram reaction for each species. Choices may be used more than once. (5pts) a. Staphylococcus aureus before the primary stain________ b. Pseudomonas aeruginosa after the primary stain __________ c. Bacillus megaterium after the addition of the mordant ____________ d. Staphylococcus aureus after decolorization _________________ e. Moraxella catarrhalis after decolorization_____________ f. Pseudomonas aeruginosa after decolorization_____________ g. Bacillus megaterium after adding the counterstain___________ h. Escherichia coli under the microscope if you forgot to apply safranin___________ i. Escherichia coli under the microscope if you forgot to apply decolorizer__________ j. Bacillus megaterium under the microscope if you forgot to apply iodine__________ A= Purple B= Red C= Colorless
Indrajeet M.
Within six months of effectively using methicillin to treat S. aureus infections in a community, all new $S$ . aureus infections were caused by MRSA. How can this best be explained? \begin{equation}\begin{array}{l}{\text { (A) A patient must have become infected with MRSA from }} \\ {\text { another community. }} \\ {\text { (B) In response to the drug, S. aureus began making drug- }} \\ {\text { resistant versions of the protein targeted by the drug. }} \\ {\text { (C) Some drug-resistant bacteria were present at the start }} \\ {\text { of treatment, and natural selection increased their }} \\ {\text { frequency. }} \\ {\text { (D) } S \text { . aureus evolved to resist vaccines. }}\end{array} \end{equation}
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