Nokea
A fecal smear from a patient with chronic diarrhea revealed cysts with four nuclei. What is the causative agent?
- A. Entamoeba histolytica
- B. Balantidium coli
- C. Giardia lamblia
- D. Trichomonas hominis
Correct Answer: A
Rationale: The correct answer is A: Entamoeba histolytica. The presence of cysts with four nuclei is characteristic of Entamoeba histolytica, a protozoan parasite causing amoebic dysentery. It forms cysts with four nuclei before maturing into trophozoites. Balantidium coli (B) is a ciliated protozoan causing balantidiasis, not known for four-nuclei cysts. Giardia lamblia (C) forms cysts with two nuclei, causing giardiasis. Trichomonas hominis (D) is a non-pathogenic flagellate found in the human colon, not associated with four-nuclei cysts.
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The generation time of Escherichia coli is
- A. 20 min
- B. 60 min
- C. 20 hours
- D. 24 hours
Correct Answer: A
Rationale: The correct answer is A (20 min) because Escherichia coli typically has a generation time of around 20 minutes, meaning the time it takes for a bacterial population to double. This rapid reproduction rate is a key characteristic of E. coli. Option B (60 min) is incorrect as it is longer than the usual generation time. Option C (20 hours) is too long for E. coli's generation time. Option D (24 hours) is also incorrect as it is much longer than the typical generation time of E. coli.
Which of the following has a higher resistance to environmental stresses than the others?
- A. Bacterial endospores
- B. Fungal spores
- C. Enveloped viruses
- D. Vegetative bacterial cells
Correct Answer: A
Rationale: The correct answer is A: Bacterial endospores. Bacterial endospores have a higher resistance to environmental stresses due to their unique structure, which includes a tough outer layer that protects the spore from harsh conditions such as heat, chemicals, and radiation. This protective layer allows endospores to remain dormant and survive in unfavorable environments until conditions improve.
Summary:
B: Fungal spores - While fungal spores can also survive in harsh conditions, they are generally not as resistant as bacterial endospores due to differences in their protective structures.
C: Enveloped viruses - Enveloped viruses are susceptible to environmental stresses as their lipid envelope can easily be damaged by heat, chemicals, and other factors.
D: Vegetative bacterial cells - Vegetative bacterial cells are more susceptible to environmental stresses compared to endospores, as they do not have the same level of protective mechanisms to survive in unfavorable conditions.
What measures should be applied to prevent hospital-acquired infections:
- A. Isolation of the source
- B. Isolation of the risk patients
- C. Measures to increase the resistance of the patient to infections
- D. All are correct
Correct Answer: D
Rationale: The correct answer is D because all measures mentioned are important in preventing hospital-acquired infections. Isolating the source helps prevent the spread of infections. Isolating at-risk patients reduces their exposure. Increasing patient resistance to infections through proper hygiene and immunizations minimizes susceptibility. Each measure plays a crucial role in infection prevention, making all options correct.
Which bacteria are capable of producing an exotoxin that causes severe diarrhea?
- A. Escherichia coli
- B. Clostridium botulinum
- C. Vibrio cholerae
- D. All of the above
Correct Answer: D
Rationale: The correct answer is D because all three bacteria listed are capable of producing exotoxins that can cause severe diarrhea. Escherichia coli can produce toxins that lead to diarrhea. Clostridium botulinum produces a neurotoxin causing botulism, which can also result in diarrhea. Vibrio cholerae is known for producing cholera toxin, a potent exotoxin that causes severe watery diarrhea. The other choices are incorrect because each bacterium listed is capable of producing a toxin that can cause diarrhea.
The biosafety level necessary in water testing facilities is level
- A. 1
- B. 2
- C. 3
- D. 4
Correct Answer: A
Rationale: The correct answer is A: 1. Water testing facilities typically handle low-risk microorganisms, hence requiring Biosafety Level 1. BSL 1 is suitable for working with well-characterized agents not known to consistently cause disease in healthy adults. BSL 2 is for moderate-risk agents, BSL 3 for high-risk agents, and BSL 4 for dangerous pathogens. Therefore, choices B, C, and D are incorrect for water testing facilities due to the low risk involved in handling the microorganisms found in water samples.