A patient with a wound infection had a Gram-positive cocci isolated from the sample. The bacteria were catalase-positive and coagulase-positive. What is the likely causative agent?

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus aureus. This is because Staphylococcus aureus is Gram-positive, catalase-positive, and coagulase-positive, which matches the characteristics described in the question. Staphylococcus epidermidis is also Gram-positive but is coagulase-negative. Streptococcus pneumoniae is Gram-positive but is catalase-negative. Enterococcus faecalis is Gram-positive but is catalase-negative and coagulase-negative. Therefore, based on the given information, Staphylococcus aureus is the likely causative agent of the wound infection.

Correct Answer: D

Rationale: The correct answer is D because during the incubation period of Salmonella Typhi infection, the bacteria multiply in the macrophages of the Peyer's patches and solitary follicles. This is supported by the fact that S. Typhi is an intracellular pathogen that targets the lymphoid tissues of the intestines. Macrophages in these areas serve as the primary host cells for the bacteria, allowing for their replication and evasion of the host immune response. Choices A, B, and C are incorrect because S. Typhi does not primarily multiply in the small intestine enterocytes, the lumen of the small intestine, or hepatocytes during the initial stages of infection.

Correct Answer: A

Rationale: The correct answer is A: 1 chromosome. Bacterial cells typically have a singular circular chromosome that contains their genetic material. This chromosome is essential for the cell's survival and contains all the necessary genetic information for its functions. Choices B, C, and D are incorrect because they refer to the chromosome numbers found in human cells (23 pairs or 46 individual chromosomes). Bacteria, being prokaryotic organisms, have a simpler genetic makeup compared to eukaryotic organisms like humans, hence they possess only one chromosome.

Correct Answer: B

Rationale: The correct answer is B: Family Reoviridae. Reassortment of gene segments occurs in segmented viruses like Reoviruses. In Reoviridae, each segment encodes a specific protein, allowing for reassortment to generate new strains. Togaviridae (A) is a non-segmented virus, not capable of reassortment. Picornaviridae (C) and Paramyxoviruses (D) are also non-segmented viruses, limiting their ability for reassortment. Therefore, the correct choice is B due to the segmented nature of Reoviruses allowing for genetic reassortment.

Correct Answer: B

Rationale: The correct answer is B: Leptospirosis. Spiral-shaped bacteria with loose coils and pointed ends are characteristic of Leptospira interrogans, the causative agent of Leptospirosis. This bacterium is typically found in contaminated water or soil and can infect humans through contact with infected animals or water. Syphilis (Choice A) is caused by the spirochete Treponema pallidum, which has a more tightly coiled shape and does not typically appear loose or pointed. Relapsing fever (Choice C) is caused by Borrelia species, which are also spirochetes but do not have the loose coils and pointed ends described. Lyme disease (Choice D) is caused by Borrelia burgdorferi, which, like Relapsing fever, does not match the morphology described.

Correct Answer: A

Rationale: Rationale: 1. Gram-positive cocci in clusters point to Staphylococcus or Micrococcus. 2. Catalase-positive eliminates Streptococcus. 3. Coagulase-positive distinguishes Staphylococcus aureus. 4. Thus, the causative agent is Staphylococcus aureus. Summary: - B: Streptococcus pyogenes is catalase-negative. - C: Enterococcus faecalis is catalase-negative. - D: Micrococcus luteus is catalase-positive but coagulase-negative.

Correct Answer: A

Rationale: The correct answer is A: Bacillus anthracis. Bacillus anthracis is the likely causative agent as it is a Gram-positive rod-shaped bacterium known to cause ulcerated lesions with associated fever and malaise. Anthrax typically presents with these symptoms and fits the description given in the question. Clostridium perfringens (Choice B) causes gas gangrene and typically presents with different symptoms. Clostridium tetani (Choice C) causes tetanus and is not associated with ulcerated lesions. Bacillus cereus (Choice D) is known for causing food poisoning and does not typically present with the symptoms described in the question.

Correct Answer: A

Rationale: The correct answer is A: Clostridium perfringens. This bacterium is Gram-positive, spore-forming, anaerobic, and produces gas. Clostridium perfringens is commonly associated with wound infections due to its ability to produce gas gangrene. Choice B: Bacillus anthracis is also a Gram-positive, spore-forming bacterium, but it does not typically produce gas in wound infections. Choice C: Clostridium botulinum is a spore-forming, anaerobic bacterium, but it is associated with foodborne botulism rather than wound infections. Choice D: Clostridium tetani is a spore-forming, anaerobic bacterium that causes tetanus, but it does not produce gas in wound infections.

Correct Answer: B

Rationale: The correct answer is B: Gamma globulin, as it is not a primary immunodeficiency disease. Primary immunodeficiency diseases are genetic disorders that affect the immune system's ability to fight infections. A: Glanzmann-Riniker hypergammaglobulinemia is a rare primary immunodeficiency characterized by elevated levels of gammaglobulins. C: Variable hypogammaglobulinemia is a primary immunodeficiency disease where there are fluctuating levels of gammaglobulins. D: Bruton hypogammaglobulinemia, also known as X-linked agammaglobulinemia, is a primary immunodeficiency characterized by a lack of B cells and gammaglobulins. In summary, B is the correct answer as gamma globulin is not a primary immunodeficiency disease, whereas A, C, and D are all examples of primary immunodeficiency diseases affecting gammaglobulins levels.