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What is the first test that you perform on the dichotomous key?
What is the first test that you perform on the dichotomous key?
Gram-stain
If your bacteria is gram-stain positive, what do you look at next? What are the two options?
If your bacteria is gram-stain positive, what do you look at next? What are the two options?
You look at shape. The two options are cocci and rods.
If you have gram-positive cocci, what is the next test?
If you have gram-positive cocci, what is the next test?
The catalase would be next.
What is the indicator of a positive catalase test?
What is the indicator of a positive catalase test?
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Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase positive, Furazolidone resistant.
Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase positive, Furazolidone resistant.
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Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase positive, Furazolidone sensitive, Coagulase: positive.
Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase positive, Furazolidone sensitive, Coagulase: positive.
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If the bacteria is furazolidone sensitive, what is the next test that you perform?
If the bacteria is furazolidone sensitive, what is the next test that you perform?
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Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase positive, Furazolidone sensitive, Coagulase: negative.
Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase positive, Furazolidone sensitive, Coagulase: negative.
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If the bacteria test negative during the catalase test, what is the next test that you perform?
If the bacteria test negative during the catalase test, what is the next test that you perform?
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Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, α-hemolysis, optochin: resistant.
Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, α-hemolysis, optochin: resistant.
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What are the three options for hemolysis?
What are the three options for hemolysis?
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If the bacteria results in α-hemolysis, what is the next test you perform?
If the bacteria results in α-hemolysis, what is the next test you perform?
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Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, α-hemolysis, optochin: sensitive.
Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, α-hemolysis, optochin: sensitive.
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If the bacteria results in β-hemolysis, what is the next test that you perform?
If the bacteria results in β-hemolysis, what is the next test that you perform?
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Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, β-hemolysis, Bacitracin: sensitive.
Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, β-hemolysis, Bacitracin: sensitive.
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If the bacteria is bacitracin negative what is the next test that is performed?
If the bacteria is bacitracin negative what is the next test that is performed?
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Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, β-hemolysis, Bacitracin: resistant, SXT: resistant.
Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, β-hemolysis, Bacitracin: resistant, SXT: resistant.
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Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, β-hemolysis, Bacitracin: resistant, SXT: sensitive.
Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, β-hemolysis, Bacitracin: resistant, SXT: sensitive.
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If the shape of the gram-positive bacteria is rod-shaped, what is the next thing that you look for?
If the shape of the gram-positive bacteria is rod-shaped, what is the next thing that you look for?
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Identify the bacteria based on the dichotomous key: Gram-positive, Rod, Spore: Present.
Identify the bacteria based on the dichotomous key: Gram-positive, Rod, Spore: Present.
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Identify the bacteria based on the dichotomous key: Gram-positive, Rod, Spore: Negative, Motility @ 25ºC: Yes.
Identify the bacteria based on the dichotomous key: Gram-positive, Rod, Spore: Negative, Motility @ 25ºC: Yes.
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If the rod-shaped, gram-positive bacteria does not have spores, what is the next thing that you look for?
If the rod-shaped, gram-positive bacteria does not have spores, what is the next thing that you look for?
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What is the indication of a positive coagulase test?
What is the indication of a positive coagulase test?
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What are the physical characteristics of α-hemolysis?
What are the physical characteristics of α-hemolysis?
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What are the physical characteristics of β-hemolysis?
What are the physical characteristics of β-hemolysis?
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What are the physical characteristics of γ-hemolysis?
What are the physical characteristics of γ-hemolysis?
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Identify the bacteria based on the dichotomous key: Gram-positive, Rod, Spore: Negative, Motility @ 25ºC: No.
Identify the bacteria based on the dichotomous key: Gram-positive, Rod, Spore: Negative, Motility @ 25ºC: No.
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If the bacteria produces γ-hemolysis, what is the next test that is performed?
If the bacteria produces γ-hemolysis, what is the next test that is performed?
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Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, γ-hemolysis, Bile Esculin Azide Agar: positive.
Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, γ-hemolysis, Bile Esculin Azide Agar: positive.
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Study Notes
Gram Stain and Initial Tests
- First test performed in microbiology dichotomous key is the Gram stain.
- If the Gram stain is positive, the next step evaluates the shape of the bacteria, categorized into cocci (spherical) and rods (bacilli).
Identifying Gram-Positive Cocci
- For gram-positive cocci, the catalase test is conducted next.
- A positive catalase test is indicated by the formation of bubbles.
Distinguishing Catalase-Positive Bacteria
- Micrococcus spp.: Identified as gram-positive cocci, catalase-positive, and resistant to furazolidone.
- Staphylococcus aureus: Identified as gram-positive cocci, catalase-positive, furazolidone-sensitive, and coagulase-positive.
- For furazolidone-sensitive bacteria, the coagulase test is the next step.
- Staphylococcus epidermidis and other coagulase-negative staphylococci are identified as gram-positive cocci, catalase-positive, furazolidone-sensitive, and coagulase-negative.
Identifying Catalase-Negative Bacteria
- If the catalase test is negative, the next test performed is for hemolysis.
- Hemolysis types include α-hemolysis (incomplete), β-hemolysis (complete), and γ-hemolysis (none).
- α-Hemolytic streptococci: Identified as catalase-negative, α-hemolytic, and optotype resistant.
- Streptococcus pneumoniae: Identified as catalase-negative, α-hemolytic, and optotyping sensitive.
Identifying β-Hemolytic Bacteria
- For β-hemolysis, the bacitracin test is performed next.
- Streptococcus pyogenes (Group A): Identified as catalase-negative, β-hemolytic, and bacitracin-sensitive.
- If bacitracin is negative, SXT testing is required.
- Streptococcus agalactiae (Group B): Identified as bacitracin-resistant and SXT-resistant.
- Streptococcus equi (Group C): Identified as bacitracin-resistant and SXT-sensitive.
Identifying Gram-Positive Rods
- For rod-shaped, gram-positive bacteria, the next step is checking for endospores.
- Bacillus spp.: Identified as gram-positive rods with present spores.
- Listeria monocytogenes: Identified as gram-positive rods, spore-negative, and motile at 25ºC.
Further Identifying Spore-Negative Rods
- If rod-shaped, gram-positive bacteria lack spores, motility at 25ºC is assessed.
- Corynebacterium spp.: Identified as spore-negative, gram-positive rods, non-motile at 25ºC.
Assessing γ-Hemolytic Bacteria
- For bacteria that produce γ-hemolysis, the Bile Esculin Azide Agar test is performed.
- Enterococcus spp.: Identified as gram-positive cocci, catalase-negative, γ-hemolytic, and bile esculin positive.
Hemolysis Characteristics
- α-Hemolysis: Incomplete hemolysis resulting in slight discoloration surrounding bacteria.
- β-Hemolysis: Complete hemolysis showing a transparent area around bacteria.
- γ-Hemolysis: No hemolysis indicating no color change in the agar surrounding bacteria.
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Description
Test your knowledge on the microbiology dichotomous key with this interactive quiz. Explore key concepts such as gram-staining and bacterial shapes to enhance your understanding of bacteria classification. Ideal for students studying microbiology or preparing for exams.
