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Which of the following is responsible for causing gonorrhea?
- A. Neisseria gonorrhoeae
- B. Chlamydia trachomatis
- C. Mycobacterium tuberculosis
- D. Treponema pallidum
Correct Answer: A
Rationale: Neisseria gonorrhoeae is the correct answer because it is the specific bacterium responsible for causing gonorrhea. It is a sexually transmitted infection that primarily affects the genital tract. Neisseria gonorrhoeae is transmitted through sexual contact and can lead to symptoms such as painful urination, discharge, and pelvic pain.
Chlamydia trachomatis (Choice B) is another sexually transmitted bacterium, but it causes chlamydia, not gonorrhea.
Mycobacterium tuberculosis (Choice C) is responsible for tuberculosis, a different infectious disease that primarily affects the lungs.
Treponema pallidum (Choice D) causes syphilis, another sexually transmitted infection that presents with distinct symptoms from gonorrhea.
Therefore, Neisseria gonorrhoeae is the correct choice for causing gonorrhea due to its specific association with this particular infection.
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A patient with a productive cough and fever had a sputum smear revealing Gram-positive cocci in pairs with a capsule. What is the most likely causative agent?
- A. Streptococcus pneumoniae
- B. Klebsiella pneumoniae
- C. Neisseria meningitidis
- D. Staphylococcus aureus
Correct Answer: A
Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is the most likely causative agent based on the description of Gram-positive cocci in pairs with a capsule. S. pneumoniae is known for its characteristic morphology and the presence of a capsule, which helps in evading the immune system. It commonly causes pneumonia, especially in patients with a productive cough and fever.
Incorrect choices:
B: Klebsiella pneumoniae typically presents with a mucoid capsule and is associated with pneumonia in immunocompromised individuals.
C: Neisseria meningitidis is a Gram-negative diplococcus and is more commonly associated with meningitis and septicemia.
D: Staphylococcus aureus is a Gram-positive cocci, but it does not typically present in pairs with a capsule and is more commonly associated with skin and soft tissue infections.
A patient with a deep tissue infection had Gram-negative rods isolated from the wound culture. The bacteria were oxidase-positive and non-lactose fermenters. What is the most likely causative agent?
- A. Pseudomonas aeruginosa
- B. Escherichia coli
- C. Klebsiella pneumoniae
- D. Shigella dysenteriae
Correct Answer: A
Rationale: The correct answer is A: Pseudomonas aeruginosa. This is because Pseudomonas is a Gram-negative rod, oxidase-positive, and non-lactose fermenter. These characteristics are typical of Pseudomonas species.
B: Escherichia coli is a Gram-negative rod but is lactose fermenter and usually oxidase-negative.
C: Klebsiella pneumoniae is a Gram-negative rod, non-lactose fermenter, but is usually oxidase-negative.
D: Shigella dysenteriae is a Gram-negative rod, non-lactose fermenter, but is usually oxidase-negative and is more associated with causing shigellosis rather than deep tissue infections.
On a certain territory mass death of rodents was registered. It was suspected that their death might have been caused by plague. What serological reaction should be applied for quick identification of antigen of the causative agent of this epizooty?
- A. Precipitation
- B. Agglutination
- C. Passive hemagglutination
- D. Complement binding
Correct Answer: B
Rationale: The correct answer is B: Agglutination. During a suspected plague outbreak, agglutination testing is used to quickly identify the antigen of the causative agent. In this test, specific antibodies are added to a sample containing the suspected antigen. If the antigen is present, it will clump together (agglutinate) with the antibodies, indicating a positive result. This method is rapid and efficient for identifying the presence of the plague-causing agent.
Choice A: Precipitation involves the formation of a visible precipitate when antigen and antibody react, but it is not as quick or specific as agglutination for identifying the antigen in this scenario.
Choice C: Passive hemagglutination is a variation of agglutination that uses red blood cells as carriers for antigens or antibodies. While it can be useful in certain situations, it is not typically the first choice for rapid identification of plague antigen.
Choice D: Complement binding is a different type of
Which bacterium is known for producing an exotoxin that causes severe diarrhea?
- A. Clostridium tetani
- B. Clostridium botulinum
- C. Vibrio cholerae
- D. Shigella dysenteriae
Correct Answer: C
Rationale: Rationale:
1. Vibrio cholerae produces cholera toxin causing severe diarrhea.
2. Clostridium tetani causes tetanus, not diarrhea.
3. Clostridium botulinum causes botulism, not diarrhea.
4. Shigella dysenteriae causes dysentery, not typical diarrhea.
Summary:
A: Incorrect, causes tetanus.
B: Incorrect, causes botulism.
C: Correct, produces cholera toxin causing severe diarrhea.
D: Incorrect, causes dysentery.
Viruses are characterised by:
- A. They have only one type of nucleic acid
- B. Their extracellular form is referred as “viroidâ€
- C. They are optional intracellular parasites
- D. Their size is measured in micrometers
Correct Answer: A
Rationale: Step 1: Viruses can have either DNA or RNA, not both, hence they have only one type of nucleic acid.
Step 2: The extracellular form of viruses is called virion, not viroid.
Step 3: Viruses are obligate intracellular parasites, meaning they rely on host cells for replication.
Step 4: Viruses are measured in nanometers, not micrometers.
Therefore, the correct answer is A.