Nokea
Autoclaving will usually destroy/inactivate all fungi, bacteria, viruses, and most bacterial spores but will not necessarily eliminate
- A. neurotoxins.
- B. prions.
- C. protozoan cysts.
- D. mycoplasmas.
Correct Answer: B
Rationale: The correct answer is B: prions. Autoclaving, a method of sterilization using high pressure and steam, is effective at destroying most microorganisms including fungi, bacteria, viruses, and most bacterial spores due to denaturation of their proteins and nucleic acids. However, prions are highly resistant infectious proteins that are not easily eliminated by autoclaving. Prions can withstand high temperatures and pressure, making them a challenge to eradicate. Neurotoxins (A), protozoan cysts (C), and mycoplasmas (D) are susceptible to autoclaving and would be destroyed during the process.
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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.
Which one is true about sexually transmitted infections?
- A. An example of sexually transmitted infection is the soft chancre
- B. Entry portal is only the mucus of the urogenital tract
- C. After the syphilis infection the developed immunity is life-lasting
- D. The sexually transmitted infections are typical for developing countries with low social status and low hygiene.
Correct Answer: A
Rationale: The correct answer is A because a soft chancre is a type of sexually transmitted infection caused by the bacterium Haemophilus ducreyi. It presents as a painless ulcer on the genitals. The other choices are incorrect. B is incorrect because STIs can enter the body through various routes, not only the urogenital tract mucosa. C is incorrect because immunity to syphilis is not lifelong; reinfection is possible. D is incorrect because STIs can occur in any country regardless of social status or hygiene levels.
In a bacteriological laboratory some bacterial smears had to be stained by Gram's method. For this purpose the following reagents were prepared: gentian violet, Lugol's solution, aqueous fuchsin solution. What other reagent is required?
- A. 96% ethanol
- B. 5% sulfuric acid
- C. Methylene blue solution
- D. Carbolic fuchsin
Correct Answer: A
Rationale: The correct answer is A: 96% ethanol. In Gram's staining method, after applying gentian violet, Lugol's solution, and aqueous fuchsin, the next step is to use a decolorizing agent like 96% ethanol to wash away the excess stain from the Gram-negative bacteria. This step is crucial as it helps differentiate between Gram-positive and Gram-negative bacteria based on their cell wall properties. The other choices are incorrect because sulfuric acid is not used in Gram's staining method, methylene blue is typically used in other staining techniques like the simple stain, and carbolic fuchsin is not a standard reagent in the Gram's staining process.
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.
Sterilization destroys all microorganisms including:
- A. vegetative cells only
- B. viruses only
- C. spores
- D. protozoa only
Correct Answer: C
Rationale: Sterilization refers to the complete elimination of all microorganisms, including their spores, which are the most resistant form of microbial life. Spores have a tough outer coating that protects them from harsh conditions, making them more difficult to destroy compared to vegetative cells, viruses, and protozoa. Therefore, the correct answer is C because sterilization targets and eliminates all forms of microorganisms, including spores. Choices A, B, and D are incorrect because sterilization goes beyond just targeting vegetative cells, viruses, or protozoa; it aims to eliminate all microorganisms present.