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Microbiology Questions: Bacterial Identification and Gram Stain

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Microbiology Questions: Bacterial Identification and Gram Stain

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Questions and Answers

The identification of bacteria by serologic tests is based on the presence of specific antigens. Which of the following bacterial components is least likely to contain useful antigens?

Cell wall

Flagella

Ribosomes (correct)

Capsule

Which of the following statements concerning the Gram stain is incorrect?

Mycoplasma pneumoniae is not visible in the Gram's stain because it does not have a cell wall

Escherichia coli stains pink because it has a thin peptidoglycan layer

Streptococcus pyogens stains blue because it has a thick peptidoglycan layer

Mycobacterium tuberculosis stains blue because it has a thick lipid layer (correct)

Why does Escherichia coli stain pink in the Gram stain?

Because it has a thick peptidoglycan layer

Because other components of its cell structure retain the pink stain

Because it has a thin peptidoglycan layer (correct)

Because it has a thick lipid layer

Why is Mycoplasma pneumoniae not visible in the Gram's stain?

<p>Because it does not have a cell wall</p> Signup and view all the answers

What is the primary reason Streptococcus pyogens stains blue in the Gram stain?

<p>It has a thick peptidoglycan layer</p> Signup and view all the answers

Study Notes

Serologic Tests for Bacteria Identification

Serologic tests identify bacteria based on the presence of specific antigens.
Ribosomes, cell wall, capsule, and flagella are bacterial components that typically contain useful antigens.
However, ribosomes are least likely to contain useful antigens.

Gram Staining

The Gram stain is used to differentiate bacteria based on their cell wall composition.
Bacteria with a thin peptidoglycan layer, such as Escherichia coli, stain pink.
Bacteria with a thick peptidoglycan layer, such as Streptococcus pyogenes, stain blue.
Mycoplasma pneumoniae lacks a cell wall, making it invisible in the Gram stain.
Mycobacterium tuberculosis stains blue due to its thick lipid layer, not its peptidoglycan layer.

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Description

Test your knowledge on the identification of bacteria using serologic tests and the principles of the Gram stain. Practice with these microbiology questions.