Podcast
Questions and Answers
Why are mycoplasmas resistant to antibiotics that inhibit cell wall synthesis?
Why are mycoplasmas resistant to antibiotics that inhibit cell wall synthesis?
- Mycoplasmas lack a cell wall (correct)
- Mycoplasmas have a thick cell wall
- Mycoplasmas have a rigid cell wall
- Mycoplasmas have a flexible cell membrane
What is the characteristic appearance of mycoplasma colonies?
What is the characteristic appearance of mycoplasma colonies?
- Rough, irregular colonies
- Smooth, circular colonies
- Tiny, 'fried egg' shaped colonies (correct)
- Large, opaque colonies
What is the role of cholesterol in the cell membrane of mycoplasmas?
What is the role of cholesterol in the cell membrane of mycoplasmas?
- Cholesterol is required for mycoplasmas to grow on cell-free media
- Cholesterol is used as an energy source by mycoplasmas
- Cholesterol provides structural rigidity to the cell membrane
- Cholesterol helps compensate for the lack of a cell wall in mycoplasmas (correct)
What is the reason for the difficulty in diagnosing mycoplasma infections?
What is the reason for the difficulty in diagnosing mycoplasma infections?
Which test is considered most diagnostic for mycoplasma infection?
Which test is considered most diagnostic for mycoplasma infection?
What characteristic feature of mycoplasma contributes to their resistance against antibiotics that inhibit cell wall synthesis?
What characteristic feature of mycoplasma contributes to their resistance against antibiotics that inhibit cell wall synthesis?
What is the significance of a high cold agglutinin titer in the diagnosis of mycoplasma infection?
What is the significance of a high cold agglutinin titer in the diagnosis of mycoplasma infection?
Why is direct microscopy of limited value in the diagnosis of Mycoplasma infections?
Why is direct microscopy of limited value in the diagnosis of Mycoplasma infections?
What is the unique characteristic of Mycoplasma's cell membrane compared to other bacteria?
What is the unique characteristic of Mycoplasma's cell membrane compared to other bacteria?
What do cold agglutinins do in the context of Mycoplasma infections?
What do cold agglutinins do in the context of Mycoplasma infections?
Which type of antibody response indicates recent Mycoplasma infection?
Which type of antibody response indicates recent Mycoplasma infection?
In what way do mycoplasmas differ from other bacteria in terms of growth requirements?
In what way do mycoplasmas differ from other bacteria in terms of growth requirements?
How do mycoplasmas compensate for their lack of a cell wall?
How do mycoplasmas compensate for their lack of a cell wall?
Why is cultivation of mycoplasmas difficult compared to other bacteria?
Why is cultivation of mycoplasmas difficult compared to other bacteria?
How do fastidious bacteria like mycoplasmas appear when observed microscopically after several days of incubation?
How do fastidious bacteria like mycoplasmas appear when observed microscopically after several days of incubation?
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Study Notes
Mycoplasma Characteristic Features
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Lack cell wall, making them resistant to antibiotics that inhibit cell wall synthesis, such as beta-lactams (e.g., penicillin and cephalosporins)
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Unstainable by the Gram stain
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Variable in shape (pleomorphic)
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Contents are enveloped by a cell membrane
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Cell membrane contains sterol in the form of cholesterol to compensate for the lack of cell wall
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The smallest bacteria that can be grown on cell-free media
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Require serum-enriched medium containing cholesterol (fastidious bacteria)
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Produce minute colonies with a characteristic “fried-egg” appearance (seen only microscopically) after several days of incubation
Mycoplasma Laboratory Diagnosis
- Diagnosis of Mycoplasma infection is based on serology
- Direct microscopy is of limited value due to inability to stain with Gram stain
- Cultivation is difficult and requires prolonged incubation (up to 3 weeks in case of M.pneumoniae)
- PCR is rapid and highly sensitive, but expensive and does not distinguish between colonization and infection
Serological Tests
- Specific tests: IgM or a fourfold rise in IgG antibody titre by ELIA is diagnostic
- Non-specific test: cold agglutinins (IgM that agglutinate RBCs at 4°C but not 37°C)
- A titre of ≥1:128 indicates recent infection
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