Questions and Answers
What color is the PEA plate?
Yellowish, like TSA control.
What type of bacteria does PEA selectively target?
Gram positive bacteria.
Name two organisms that grow on PEA.
Enterococcus faecalis and Staphylococcus epidermidis.
What is the selective agent in PEA?
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PEA is an undefined, ____ medium.
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What does a positive test on PEA look like?
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What does a negative test on PEA look like?
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Why is PEA not considered a differential medium?
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What type of bacteria is PEA designed to isolate?
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What color change indicates fermentation in MSA?
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What is the primary purpose of Snyder agar?
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What pH does Snyder agar start at?
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What is a positive result in the catalase test?
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What is the function of the catalase enzyme?
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What characterizes fastidious microorganisms?
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What is the purpose of the indicators in differential media?
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Study Notes
Phenylethyl Alcohol Agar Overview
- Phenylethyl Alcohol Agar (PEA) is a selective medium primarily for Gram-positive bacteria.
- Yellowish color resembles TSA control, indicating successful growth of organisms.
Selectivity and Purpose
- PEA inhibits Gram-negative bacteria by hindering DNA synthesis, promoting Gram-positive growth.
- Useful for isolating Staphylococci, Streptococci, Enterococci, and some Lactococci.
Media Composition
- Contains phenyl ethyl alcohol which selectively inhibits bacteria.
- Nutritional components include digests of casein and soybean meal and sodium chloride for osmotic stability.
Growth and Inhibition Indicators
- Good growth indicates the organism is likely staphylococcus, streptococcus, enterococcus, or lactococcus.
- Poor growth suggests the organism is probably Gram-negative, inhibited by phenylethyl alcohol.
Test Results Interpretation
- Positive test: Good growth (indicating Gram-positive).
- Negative test: Poor or no growth (indicating Gram-negative).
Differential Nature
- PEA is not differential; it does not distinguish between different Gram-positive organisms.
Related Tests and Media
- Mannitol Salt Agar (MSA) has a 7.5% concentration of salt, selects for staphylococci.
- Varies in color; initially red, changes to yellow when fermentation occurs.
- Snyder Agar is used for testing oral bacteria related to dental caries, works on principles of acidity and sugar fermentation.
Catalase Test
- The catalase test differentiates between catalase-positive bacteria (like Staphylococcus) and catalase-negative bacteria (like Streptococcus).
- Observing bubbles upon adding hydrogen peroxide indicates a positive result.
Selective and Differential Component Purposes
- Inhibitors in the medium exploit weaknesses of specific bacteria.
- Substrates allow for differential identification based on chemical reactions.
- Indicators make visible reactions in differential media.
Hemolysis Types in Blood Agar
- Beta hemolysis: complete lysis of red blood cells.
- Alpha hemolysis: incomplete lysis, appears green.
- Gamma hemolysis: no lysis.
Fastidious Organisms
- Definition: Microorganisms with strict growth conditions, difficult to culture without specific requirements.
Importance of Test Techniques
- Streak-stab technique enhances streptolysin activity by reducing oxygen in the subsurface environment, aiding in the identification of specific organisms.
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Description
This quiz contains flashcards covering key concepts of Phenylethyl Alcohol Agar, including its selective characteristics and specific organisms that grow on it. Perfect for microbiology students looking to master their understanding of bacterial growth media.
