A patient with a sore throat had a throat smear revealing Gram-positive cocci in pairs. The bacteria were catalase-negative and beta-hemolytic. What is the most likely causative agent?

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pyogenes. Rationale: 1. Gram-positive cocci in pairs suggest Streptococcus species. 2. Catalase-negative rules out Staphylococcus. 3. Beta-hemolytic indicates Streptococcus pyogenes due to its beta-hemolytic properties. Summary: B: Streptococcus pneumoniae is catalase-negative but not beta-hemolytic. C: Enterococcus faecalis is not typically beta-hemolytic. D: Staphylococcus aureus is catalase-positive and not typically in pairs.

Correct Answer: C

Rationale: The correct answer is C: Chronic atrophic rhinitis. This infection is typical for the upper respiratory tract as it affects the nasal mucosa and sinuses. It is characterized by inflammation and atrophy of the nasal mucosa. Psittacosis (A) is a zoonotic infection transmitted from birds, affecting the lungs. Mycoplasma bronchitis (B) is a lower respiratory tract infection caused by Mycoplasma pneumoniae. Legionnaires disease (D) is a severe form of pneumonia caused by Legionella bacteria. Therefore, C is the correct answer as it specifically pertains to the upper respiratory tract.

Correct Answer: B

Rationale: The correct answer is B: Pseudomonas aeruginosa. P. aeruginosa is known for producing pyocyanin, a green pigment. This bacterium is commonly associated with infections in immunocompromised individuals. Staphylococcus aureus (choice A) produces golden-yellow pigments, not green. Escherichia coli (choice C) and Clostridium difficile (choice D) do not produce pyocyanin. Therefore, the correct choice is B based on the characteristic pigment produced by Pseudomonas aeruginosa.

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: D

Rationale: The correct answer is D: Bacillus cereus. Bacillus intoxication is typically caused by Bacillus cereus, which is a common foodborne pathogen. This bacterium produces toxins that can lead to gastrointestinal illness when ingested. Bacillus subtilis (A) and Bacillus thuringiensis (B) are not known to cause intoxication in humans. Bacillus anthracis (C) causes anthrax, not intoxication. Therefore, Bacillus cereus is the correct choice for Bacillus intoxication.

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: C

Rationale: The correct answer is C. Bacterial spores are NOT used for cell division. Bacterial spores are dormant, resistant forms of bacteria that are formed in response to harsh environmental conditions. They are not involved in cell division but rather serve as a survival mechanism for the bacteria. A: They can deform the cell or not - This is true. Bacterial spores can deform the cell or not depending on the conditions. B: They can be terminal, subterminal, and central - This is true. Bacterial spores can be located at different positions within the bacterial cell. D: They are formed for 6-8h - This is incorrect. The formation of bacterial spores can take variable time periods depending on the species and environmental conditions.

Correct Answer: B

Rationale: The correct answer is B: mycorrhizae. Mycorrhizae are symbiotic fungi that form a mutualistic relationship with plant roots, aiding in the absorption of minerals and water. They enhance the plant's nutrient uptake capacity, promoting plant growth and health. Decomposers (A) break down dead organic matter, yeasts (C) are single-celled fungi used in fermentation, and molds (D) are fungi that grow in multicellular filaments. These options do not specifically assist plant roots in mineral and water absorption like mycorrhizae do.

Correct Answer: B

Rationale: The correct answer is B because a viral capsid is a protein coat that surrounds and protects the viral nucleic acid (DNA or RNA). It helps in the attachment of the virus to host cells and protects the genetic material during transmission. Choice A is incorrect because a viral capsid is composed of proteins, not an envelope. Choice C is incorrect because not all viruses have an outer membrane. Choice D is incorrect because a viral capsid is primarily made up of proteins, not lipids.