Microbiology Dichotomous Key Quiz

Questions and Answers

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?

You look at shape. The two options are cocci and rods.

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?

Bubbles Signup and view all the answers

Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase positive, Furazolidone resistant.

Micrococcus spp. Signup and view all the answers

Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase positive, Furazolidone sensitive, Coagulase: positive.

Staphylococcus aureus Signup and view all the answers

If the bacteria is furazolidone sensitive, what is the next test that you perform?

The Coagulase test Signup and view all the answers

Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase positive, Furazolidone sensitive, Coagulase: negative.

Staphylococcus epidermis and other CNS Signup and view all the answers

If the bacteria test negative during the catalase test, what is the next test that you perform?

Hemolysis Signup and view all the answers

Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, α-hemolysis, optochin: resistant.

α-hemolytic streptococci (usually oral strep) Signup and view all the answers

What are the three options for hemolysis?

α, β, and γ-hemolysis Signup and view all the answers

If the bacteria results in α-hemolysis, what is the next test you perform?

Optochin Signup and view all the answers

Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, α-hemolysis, optochin: sensitive.

Streptococcus pneumoniae Signup and view all the answers

If the bacteria results in β-hemolysis, what is the next test that you perform?

Bacitracin Signup and view all the answers

Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, β-hemolysis, Bacitracin: sensitive.

Streptococcus pyogenes (Group A) Signup and view all the answers

If the bacteria is bacitracin negative what is the next test that is performed?

SXT Signup and view all the answers

Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, β-hemolysis, Bacitracin: resistant, SXT: resistant.

Streptococcus agalactiae (Group B) Signup and view all the answers

Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, β-hemolysis, Bacitracin: resistant, SXT: sensitive.

Streptococcus equi (Group C) Signup and view all the answers

If the shape of the gram-positive bacteria is rod-shaped, what is the next thing that you look for?

You look for endospores. Signup and view all the answers

Identify the bacteria based on the dichotomous key: Gram-positive, Rod, Spore: Present.

Bacillus spp. Signup and view all the answers

Identify the bacteria based on the dichotomous key: Gram-positive, Rod, Spore: Negative, Motility @ 25ºC: Yes.

Listeria monocytogenes Signup and view all the answers

If the rod-shaped, gram-positive bacteria does not have spores, what is the next thing that you look for?

You observe the motility at 25ºC. Signup and view all the answers

What is the indication of a positive coagulase test?

Clumping Signup and view all the answers

What are the physical characteristics of α-hemolysis?

Incomplete hemolysis which shows a small area discoloration and transparency surrounding the bacteria. Signup and view all the answers

What are the physical characteristics of β-hemolysis?

Complete hemolysis which shows a large area of discoloration and transparency. You can see through a portion of the area surrounding the bacteria. Signup and view all the answers

What are the physical characteristics of γ-hemolysis?

No hemolysis. You should observe no change in the color of the agar. Signup and view all the answers

Identify the bacteria based on the dichotomous key: Gram-positive, Rod, Spore: Negative, Motility @ 25ºC: No.

Corynebacterium spp. Signup and view all the answers

If the bacteria produces γ-hemolysis, what is the next test that is performed?

Bile Esculin Azide Agar Signup and view all the answers

Identify the bacteria based on the dichotomous key: Gram-positive, Cocci, Catalase: negative, γ-hemolysis, Bile Esculin Azide Agar: positive.

Enterococcus spp. Signup and view all the answers

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.