Questions and Answers
What do you look for in the Blood agar test regarding hemolysins?
production of hemolysins
In the blood agar test, what does a green sheen indicate?
Alpha hemolysis by Streptococcus pneumoniae
What is the result of complete destruction of RBCs and hemoglobin in the blood agar test?
Beta hemolysis by Streptococcus pyogenes and Staphylococcus aureus
What does no hemolysis indicate in the blood agar test?
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In the MSA test, it contains phenol red which acts as a ____________.
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What type of bacteria does the MSA test select for?
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What type of media does Mannitol in MSA make it?
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What test is performed with MSA?
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In the MSA test, bright yellow growth indicates a positive result for what?
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What does pink growth indicate in the MSA test?
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What is the Phenylethyl alcohol agar test selective for?
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Phenylethyl alcohol agar is used to _________ staph and strep.
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What is MacConkey agar selective for?
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In MacConkey agar, the bile salts and crystal red inhibit what?
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What does MacConkey agar differentiate for?
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What types of media is the Eosin Methylene Blue agar?
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What does the EMB test select for?
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What type of bacteria does the EMB test differentiate for?
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In the EMB test, eosin Y and methylene blue inhibit what?
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What test is being performed with the EMB test?
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In the Hektoen Enteric Agar test, the bile salts inhibit what?
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The Hektoen Enteric Agar differentiates for what?
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What does the MR test for?
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What does the VP test measure?
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What color indicates a positive result in the MR test?
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Why is mannitol salt agar considered both selective and differential?
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What are examples of differential media types?
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Describe MacConkey agar.
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What causes the appearance of red or pink colonies in MacConkey agar?
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What does a pink color indicate on MacConkey agar?
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Describe the EMB Agar plate.
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What is the role of Eosin and Methylene Blue in EMB?
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Match the following results seen on EMB plate:
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What are examples of bacteria that ferment lactose?
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Study Notes
Hemolysins
- Hemolysins are substances produced by bacteria that can lyse red blood cells.
- In the Blood agar test, their presence indicates the capability of bacteria to cause hemolysis.
Alpha Hemolysis
- Alpha hemolysis describes partial lysis of red blood cells, resulting in a greenish discoloration surrounding colonies.
- Streptococcus pneumoniae is a common example associated with alpha hemolysis.
Beta Hemolysis
- Beta hemolysis indicates complete lysis of red blood cells and hemoglobin, leading to a clear zone around colonies.
- Common examples include Streptococcus pyogenes and Staphylococcus aureus.
Gamma Hemolysis
- Gamma hemolysis refers to no hemolysis observed on blood agar, indicating that the bacteria do not lyse red blood cells.
pH Indicator
- Phenol red is a pH indicator used in Mannitol Salt Agar (MSA) that turns yellow in low pH conditions, indicating fermentation.
Staphylococcus (spp.)
- The MSA test contains 7.5% NaCl, selectively favoring the growth of staphylococci while inhibiting other bacteria.
Differential Media
- MSA includes mannitol for differentiating between Staphylococcus aureus (manitol fermenter) and Staphylococcus epidermidis (non-fermenter).
Mannitol Salt Agar (MSA)
- MSA is utilized for isolating and identifying staphylococci based on their ability to ferment mannitol.
S. aureus Fermenting Mannitol
- Bright yellow growth on MSA signifies a positive result for mannitol fermentation, indicating the presence of S. aureus.
Non-S. aureus Staphylococcus
- Pink growth on MSA signifies that the bacteria do not ferment mannitol, indicating other staphylococci species.
Gram Positive Selection
- Phenylethyl Alcohol Agar (PEA) is selective for Gram-positive bacteria by inhibiting Gram-negative bacteria.
Isolation
- PEA is employed to isolate staphylococci and streptococci from mixed cultures.
Gram Negative Selection
- MacConkey Agar is designed to select for Gram-negative bacteria.
Inhibition by Bile Salts
- In MacConkey Agar, bile salts and crystal violet inhibit the growth of Gram-positive organisms.
Lactose Fermenters
- MacConkey Agar differentiates lactose fermenters, which produce acid as a byproduct, from non-fermenters.
Type of Media
- Eosin Methylene Blue (EMB) Agar serves as both selective and differential media.
Selection of Gram Negative Bacteria
- EMB is specifically selective for Gram-negative bacteria.
Enteric Bacteria Differentiation
- The EMB test differentiates enteric bacteria, primarily those found in the intestinal tract.
Inhibition of Gram Positive Bacteria
- Eosin Y and methylene blue in EMB inhibit the growth of Gram-positive bacteria.
EMB Test
- EMB test is conducted to isolate and differentiate Gram-negative intestinal pathogens.
Inhibition in Hektoen Enteric Agar
- Bile salts in Hektoen Enteric Agar inhibit Gram-positive bacteria.
Differentiation for Enterics
- Hektoen Enteric Agar differentiates for enterics, particularly Salmonella and Shigella.
Mixed Acid Fermentation
- The Methyl Red (MR) test is conducted to detect mixed acid fermentation.
Neutral Fermentation Products
- The Voges-Proskauer (VP) test evaluates neutral fermentation products.
Positive MR Test Color
- A positive result in the MR test yields a red color, indicating acid production.
Selective and Differential Nature of MSA
- MSA's selectivity stems from high salt concentration; its differential nature arises from mannitol fermentation and phenol red indicator.
Examples of Differential Media
- Common types include MacConkey Agar, Eosin Methylene Blue Agar, and Mannitol Salt Agar.
MacConkey Agar Description
- MacConkey Agar functions as both selective for Gram-negative bacteria and differential for lactose fermenters.
Red or Pink Colonies in MacConkey Agar
- Red or pink colonies appear when organisms like E. coli produce acid, lowering the pH below 6.8.
Visual MacConkey Agar Results
- Pink indicates a positive result for lactose fermentation.
EMB Agar Description
- Eosin Methylene Blue Agar is selective and differential, primarily targeting Gram-negative intestinal pathogens.
Role of Eosin and Methylene Blue
- These dyes inhibit most Gram-positive bacteria while coloring colonies based on acid production from lactose fermentation.
EMB Plate Result Reasoning
- Green metallic sheen indicates high acid production; pink shows small acid production, while colorless signifies no fermentation.
Lactose Fermenters Examples
- Common lactose fermenters include Escherichia coli, Enterobacter, and Klebsiella.
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Description
Test your knowledge on selective and differential media with this quiz. Each flashcard focuses on key terms like hemolysins and various types of hemolysis observed in blood agar tests. Ideal for microbiology students looking to reinforce their understanding of bacterial identification techniques.
