How are plant bacterial pathogens identified into Gram positive and negative?

Question

BlackTom AI · Accepted Answer

Chemical and structural properties of the cell wall determine Gram classification, so the correct answer is "Chemical and structural properties of the cell wall."

Relevant knowledge points:
- Gram staining differentiates bacteria by cell wall architecture: Gram-positive bacteria have a thick peptidoglycan layer with teichoic acids; Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane containing lipopolysaccharide (LPS).
- The staining outcome depends on how the cell wall retains dyes through the decolorization step.

Step-by-step reasoning process:
1. Perform Gram stain: apply crystal violet (primary stain), add iodine (mordant), decolorize with alcohol or acetone, then counterstain with safranin.
2. In Gram-positive cells, the thick peptidoglycan matrix traps the crystal violet–iodine complex during decolorization, so cells appear purple.
3. In Gram-negative cells, the alcohol disrupts the outer membrane and the thin peptidoglycan cannot retain the crystal violet–iodine complex; these cells lose the primary stain and take up safranin, appearing pink/red.
4. Chemical tests (e.g., KOH string test) and electron microscopy can further confirm presence/absence of outer membrane and relative peptidoglycan thickness.

Why the correct answer is correct:
- The Gram reaction is a direct consequence of cell wall chemistry and structure; therefore classification into Gram-positive or Gram-negative depends on those properties rather than symptoms, visible fruiting bodies, or insect transmission.

Why the other options are incorrect:
- General symptoms: Plant disease symptoms are caused by many types of pathogens and are not diagnostic of bacterial Gram status.
- Fruiting bodies: These are fungal structures; bacteria do not form macroscopic fruiting bodies visible under a dissecting microscope.
- Transmission by insect vectors: Both Gram-positive and Gram-negative bacteria can be insect-transmitted; vectoring does not indicate Gram classification.
- "All options are correct" is false because the preceding three are incorrect.

Conclusion: The correct option—Chemical and structural properties of the cell wall—matches the provided answer.

How are plant bacterial pathogens identified into Gram positive and negative?单项选择题

类似问题

Which type of bacteria has a thick peptidoglycan layer and stains purple in Gram staining?

Which of the following is TRUE concerning direct Gram stains?

When making a Gram stain of E. coli, the iodine step was omitted. Which of the following would be the expected result of this error?

Which of the following is NOT a reason for inconsistent Gram stain results?

The technique of Gram-staining characterizes microbes based on what characteristic?

Within the Gram stain procedure, which particular step plays the critical role in differentiating between gram-positive and gram-negative cells?

What would be the likely consequence if you forgot to heat fix a smear before performing a Gram stain?

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