A duodenal content smear of a patient with indigestion contains protozoa 10-18 mcm large. They have piriform bodies, 4 pairs of filaments, two symmetrically located nuclei in the broadened part of body. What kind of the lowest organisms is it?

Correct Answer: A

Rationale: The correct answer is A: Lamblia. The description matches the characteristics of Giardia lamblia - a protozoan parasite that causes giardiasis. The piriform bodies, 4 pairs of filaments, and two symmetrically located nuclei are specific to Giardia lamblia. It is important to differentiate it from the other choices. Dysentery ameba (choice B) typically has a single nucleus and lacks the specific characteristics described. Trichomonas (choice C) is a flagellated protozoan with different morphology and does not match the given description. Intestinal ameba (choice D) such as Entamoeba histolytica usually has a single nucleus and different body shape compared to the described organism.

Correct Answer: B

Rationale: The correct answer is B: Bordetella pertussis. This bacterium causes whooping cough by infecting the respiratory tract. It produces toxins that lead to severe coughing fits characteristic of the disease. Clostridium botulinum (A) causes botulism, Streptococcus pneumoniae (C) causes pneumonia, and Neisseria meningitidis (D) causes meningitis, not whooping cough. B. pertussis is the only bacterium specifically associated with whooping cough.

Correct Answer: A

Rationale: The correct answer is A: Ziehl-Neelsen staining method. This method is used to detect acid-fast bacteria like Mycobacterium tuberculosis. Step-by-step rationale: 1. Acid-fast bacteria resist decolorization with acid-alcohol. 2. The red bacilli seen in the smear indicate acid-fast bacteria. 3. Ziehl-Neelsen stain uses carbol fuchsin to stain acid-fast bacteria red. 4. The blue background is likely the counterstain methylene blue. Incorrect choices: B: Gram stain is for categorizing bacteria into Gram-positive or Gram-negative, not specific for acid-fast bacteria. C: Giemsa stain is used for blood films and detecting parasites, not acid-fast bacteria. D: Neisser stain is not a standard microbiological staining method.

Correct Answer: C

Rationale: Nigrosin is used in negative staining, where the background is stained instead of the cells themselves. This technique helps highlight the morphology and structure of cells that may be damaged by traditional staining methods. Nigrosin is negatively charged and repels the negatively charged bacterial cells, resulting in a clear halo around the cells. This process is particularly useful for observing capsules and determining cell size and shape. The other options are incorrect because simple staining uses a single dye to color the entire cell, gram staining involves a series of dyes to differentiate between gram-positive and gram-negative bacteria, and acid-fast staining is used to detect acid-fast organisms like Mycobacterium.

Correct Answer: B

Rationale: The correct answer is B: RG2. RG2 is appropriate for agents associated with human disease that pose a moderate health risk. These agents may cause disease of varying severity, but generally do not result in serious health consequences. Other choices are incorrect because: A: RG1 is for agents not associated with disease in healthy adults, C: RG3 is for agents associated with serious or lethal human disease, and D: RG4 is for agents that pose a high risk of life-threatening disease and for which there are no treatments.

Correct Answer: B

Rationale: The correct answer is B: Linnaeus. Linnaeus developed the binomial system of nomenclature in the 18th century. He introduced the use of a two-part naming system consisting of a genus name and a species name, known as binomial nomenclature. This system helps in organizing and categorizing living organisms systematically. Pasteur (choice A) is known for his contributions to microbiology, not nomenclature. Martini (choice C) and Jenner (choice D) are not associated with the development of the binomial system of nomenclature.

Correct Answer: B

Rationale: The correct answer is B: Vibrio cholerae. Cholera is caused by this specific bacterium. Vibrio cholerae produces a toxin that leads to severe diarrhea and dehydration. Salmonella typhi causes typhoid fever, Escherichia coli can cause various infections but not cholera, and Shigella dysenteriae causes dysentery, not cholera. Therefore, the correct choice is B.

Correct Answer: C

Rationale: The Gram stain process involves staining bacterial cells with crystal violet and iodine, followed by decolorization and counterstaining. The primary differentiation is based on the cell wall structure, distinguishing bacteria into Gram-positive (retain purple color) and Gram-negative (lose purple color). This classification is crucial in microbiology for treatment decisions as it correlates with different antibiotic susceptibilities. Choices A, B, and D are incorrect because the Gram stain process does not primarily focus on flagella, shape, or motility of bacteria.

Correct Answer: C

Rationale: The correct answer is C: Papillomaviruses. Papillomaviruses are primarily transmitted through sexual contact, as they infect the skin and mucous membranes of the genital area. This transmission route is well-documented through research and epidemiological studies. Arenaviruses (A) are primarily transmitted through contact with infected rodents, not sexual contact. Togaviruses (B) are mainly transmitted by mosquitoes and ticks. Polyomaviruses (D) are typically spread through respiratory secretions or contaminated urine, not through sexual contact. Therefore, the most appropriate choice for viruses transmitted mainly through sexual contact is Papillomaviruses (C).