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A patient with a productive cough and fever had a Gram-positive cocci isolated from a sputum sample. The bacteria were catalase-positive and coagulase-negative. What is the likely microorganism?
- A. Staphylococcus epidermidis
- B. Staphylococcus aureus
- C. Streptococcus pneumoniae
- D. Neisseria meningitidis
Correct Answer: A
Rationale: The correct answer is A: Staphylococcus epidermidis.
1. Gram-positive cocci suggest a staphylococcal species.
2. Catalase-positive indicates it belongs to the Staphylococcus genus.
3. Coagulase-negative rules out Staphylococcus aureus.
4. Staphylococcus epidermidis is a common cause of infections in immunocompromised patients.
Summary:
- B: Staphylococcus aureus is coagulase-positive.
- C: Streptococcus pneumoniae is a Gram-positive diplococci.
- D: Neisseria meningitidis is a Gram-negative diplococci.
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Which bacteria are capable of producing exotoxins?
- A. Clostridium tetani
- B. Staphylococcus aureus
- C. Escherichia coli
- D. All of the above
Correct Answer: D
Rationale: The correct answer is D: All of the above. Clostridium tetani, Staphylococcus aureus, and Escherichia coli are all capable of producing exotoxins. Exotoxins are proteins released by bacteria that can cause damage to the host. Clostridium tetani produces tetanospasmin, causing tetanus. Staphylococcus aureus produces toxins like enterotoxin and toxic shock syndrome toxin-1. Escherichia coli can produce Shiga toxin and heat-labile toxin. Therefore, all three bacteria listed can produce exotoxins, making choice D the correct answer. Choices A, B, and C are incorrect as they do not encompass all the bacteria capable of producing exotoxins.
The generation time of Escherichia Coli is:
- A. 20 minutes
- B. 60 minutes
- C. 20 hours
- D. 24 hours
Correct Answer: A
Rationale: The correct answer is A: 20 minutes. Escherichia coli has a short generation time, typically around 20 minutes. This means that under ideal conditions, one bacterium can divide and produce two daughter cells every 20 minutes. This rapid growth rate is a characteristic of E. coli and is important in various fields such as microbiology and biotechnology. Choice B (60 minutes) and Choice C (20 hours) are incorrect as they do not align with the typical generation time of E. coli. Choice D (24 hours) is also incorrect as it is too long for the generation time of E. coli.
A patient with suspicion on epidemic typhus was admitted to the hospital. Some arachnids and insects have been found in his flat. Which of them may be a carrier of the pathogen of epidemic typhus?
- A. Lice
- B. Spiders
- C. Bed-bugs
- D. Cockroaches
Correct Answer: A
Rationale: The correct answer is A: Lice. Lice, specifically body lice (Pediculus humanus corporis), are known carriers of the pathogen Rickettsia prowazekii, which causes epidemic typhus. Body lice are commonly found in unsanitary conditions and can transmit the bacteria through their bites. Spiders (choice B), bed-bugs (choice C), and cockroaches (choice D) are not known vectors of epidemic typhus. Spiders are predators that do not transmit diseases to humans, while bed-bugs and cockroaches are associated with other health issues but not epidemic typhus transmission.
Which bacteria produce a toxin that inhibits protein synthesis?
- A. Shigella dysenteriae
- B. Clostridium botulinum
- C. Streptococcus pneumoniae
- D. Mycobacterium tuberculosis
Correct Answer: A
Rationale: The correct answer is A: Shigella dysenteriae. This bacteria produces the Shiga toxin, which inhibits protein synthesis by interfering with the ribosomes. Shigella dysenteriae causes severe gastrointestinal illness. The other choices, B: Clostridium botulinum, produces a neurotoxin that blocks neurotransmitter release. C: Streptococcus pneumoniae causes pneumonia and other respiratory infections. D: Mycobacterium tuberculosis causes tuberculosis by infecting the lungs. Thus, based on the toxin production and mode of action, Shigella dysenteriae is the correct answer.
A patient with diarrhea had stool microscopy revealing large, oval protozoa with a single nucleus and four flagella. What is the most likely causative agent?
- A. Giardia lamblia
- B. Entamoeba histolytica
- C. Balantidium coli
- D. Trichomonas vaginalis
Correct Answer: A
Rationale: Step 1: Large, oval protozoa with a single nucleus and four flagella indicate Giardia lamblia.
Step 2: Giardia lamblia is a flagellated protozoan causing diarrhea.
Step 3: It has a distinct appearance under microscopy.
Step 4: Entamoeba histolytica causes dysentery with no flagella.
Step 5: Balantidium coli is a ciliated protozoan with a larger size.
Step 6: Trichomonas vaginalis lacks a cyst stage and causes genitourinary infections.