Nokea
Francisella tularensis is:
- A. Gram-positive coccobacillus
- B. gram-negative coccus
- C. gram-negative bacterium
- D. Gram-negative coccobacillus
Correct Answer: D
Rationale: The correct answer is D: Gram-negative coccobacillus. Francisella tularensis is a Gram-negative coccobacillus because it has a unique shape that is between a coccus (spherical) and a bacillus (rod-shaped) and it stains pink/red in the Gram staining process. It is important to note that it is not a coccus (choice B) or a Gram-positive bacterium (choice A). Choice C is too general and does not specify the coccobacillus shape of F. tularensis. So, the correct answer is D due to its specific characteristics as a Gram-negative coccobacillus.
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A patient with pneumonia had sputum stained by the Gram method. The smear revealed Gram-positive cocci in pairs with a capsule. What is the most likely causative agent?
- A. Streptococcus pneumoniae
- B. Staphylococcus aureus
- C. Neisseria meningitidis
- D. Klebsiella pneumoniae
Correct Answer: A
Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is a common cause of pneumonia and is known to appear as Gram-positive cocci in pairs with a capsule. The presence of a capsule is a key characteristic of S. pneumoniae. Staphylococcus aureus (B) is a Gram-positive cocci but typically does not have a capsule. Neisseria meningitidis (C) is a Gram-negative diplococcus, not a Gram-positive cocci. Klebsiella pneumoniae (D) is a Gram-negative rod, not a Gram-positive cocci. Therefore, based on the staining pattern and the presence of a capsule, Streptococcus pneumoniae is the most likely causative agent in this case.
A 25-year-old woman is complaining of burning and painful urination. The microbiological analysis detects significant bacterial growth only on blood agar and it is without hemolysis. Gram-positive cocci are observed on microscopic slides. Which bacterium is the most probable cause?
- A. Proteus mirabilis
- B. Staphylococcus saprophytic
- C. Staphylococcus aureus
- D. Pseudomonas aeruginosa
Correct Answer: B
Rationale: The correct answer is Staphylococcus saprophyticus (choice B). This bacterium is a common cause of urinary tract infections in young women. It typically grows on blood agar without hemolysis and appears as Gram-positive cocci under the microscope. Proteus mirabilis (choice A) is known for urease production, causing alkaline urine. Staphylococcus aureus (choice C) is a common cause of skin and soft tissue infections, not urinary tract infections. Pseudomonas aeruginosa (choice D) is an opportunistic pathogen often seen in nosocomial infections, not typically associated with urinary tract infections in healthy individuals.
The bacterial structure that protects against desiccation is:
- A. Capsule
- B. Flagella
- C. Endospore
- D. Pili
Correct Answer: C
Rationale: The correct answer is C: Endospore. Endospores are highly resistant structures formed by certain bacterial species to withstand harsh conditions like desiccation. They contain a tough outer layer that protects the bacterial DNA and other essential components. Capsules (choice A) provide protection against host immune responses but not specifically against desiccation. Flagella (choice B) are used for bacterial motility. Pili (choice D) are involved in bacterial adhesion but do not protect against desiccation. Therefore, endospores are the most suitable choice for protecting against desiccation.
Which bacteria produce a toxin that causes botulism?
- A. Clostridium tetani
- B. Clostridium botulinum
- C. Staphylococcus aureus
- D. Bacillus anthracis
Correct Answer: B
Rationale: The correct answer is B: Clostridium botulinum. This bacterium produces the botulinum toxin, which causes botulism by blocking nerve functions. Clostridium tetani causes tetanus, not botulism. Staphylococcus aureus produces toxins that cause food poisoning, not botulism. Bacillus anthracis causes anthrax, not botulism. Therefore, the correct choice is Clostridium botulinum because it is the specific bacterium responsible for producing the toxin that leads to botulism.
Which of the following is true regarding bacterial plasmids?
- A. Plasmids are essential for bacterial survival
- B. Plasmids are circular DNA molecules
- C. Plasmids are never involved in antibiotic resistance
- D. Plasmids are found in all bacteria
Correct Answer: B
Rationale: Correct Answer: B - Plasmids are circular DNA molecules
Rationale:
1. Plasmids are extrachromosomal DNA molecules found in bacteria.
2. Plasmids are typically circular in structure, not linear.
3. Circular plasmids are easily replicated and transferred between bacteria.
4. Plasmids can carry genes for antibiotic resistance, making option C incorrect.
5. Not all bacteria have plasmids, making option D incorrect.
6. While plasmids can provide benefits, they are not essential for bacterial survival, making option A incorrect.