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1. What are the three main shapes of bacteria and how are they named? Give an example of each shape.
- The three main shapes of bacteria are cocci (spherical), bacilli (rod-shaped) and spirilla (spiral). They are named based on their shape
and arrangement, such as staphylococci (clusters of cocci), streptobacilli (chains of bacilli) and spirochetes (flexible spirilla). Examples of
each shape are Staphylococcus aureus, Escherichia coli and Treponema pallidum, respectively.
- Rationale: This question tests the students' knowledge of basic bacterial morphology and nomenclature, which is important for
identifying and classifying different types of bacteria.
2. What is the difference between gram-positive and gram-negative bacteria? How does this affect their susceptibility to antibiotics?
- Gram-positive and gram-negative bacteria differ in the structure of their cell wall, which determines how they react to the Gram stain.
Gram-positive bacteria have a thick layer of peptidoglycan that retains the purple dye, while gram-negative bacteria have a thin layer of
peptidoglycan and an outer membrane that prevents the dye from entering. This affects their susceptibility to antibiotics because some
antibiotics target the peptidoglycan layer, such as penicillin, which is more effective against gram-positive bacteria. Other antibiotics
target the outer membrane, such as polymyxin, which is more effective against gram-negative bacteria.
- Rationale: This question tests the students' understanding of the Gram stain technique and its clinical implications for choosing
appropriate antibiotics.
3. What are the four phases of bacterial growth curve and what happens in each phase?
- The four phases of bacterial growth curve are lag phase, log phase, stationary phase and death phase. In the lag phase, the bacteria
adapt to the new environment and prepare for division. In the log phase, the bacteria multiply exponentially at a constant rate. In the
stationary phase, the bacterial growth is balanced by death due to nutrient depletion or waste accumulation. In the death phase, the
bacteria die faster than they grow due to unfavorable conditions.
- Rationale: This question tests the students' ability to describe the dynamics of bacterial population growth and its factors.
4. What are endospores and why are they important for bacterial survival?
- Endospores are dormant structures formed by some bacteria when they encounter harsh conditions, such as high temperature, low
pH or lack of nutrients. They are resistant to heat, chemicals and radiation, and can survive for long periods of time until favorable
conditions return. They are important for bacterial survival because they allow them to persist in hostile environments and re-establish
infection when conditions improve.
- Rationale: This question tests the students' knowledge of endospore formation and function, which is relevant for infection control
and prevention.
5. What are the three main mechanisms of horizontal gene transfer in bacteria and how do they differ?
- The three main mechanisms of horizontal gene transfer in bacteria are transformation, transduction and conjugation. They differ in
the source and mode of transfer of genetic material. Transformation involves the uptake of free DNA from the environment by
competent cells. Transduction involves the transfer of DNA from one bacterium to another by a bacteriophage (virus). Conjugation
involves the direct transfer of DNA from one bacterium to another by a sex pilus (a tube-like structure).
- Rationale: This question tests the students' comprehension of horizontal gene transfer, which is a major source of genetic diversity
and antibiotic resistance in bacteria.
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