Correct Answer: C

Rationale: The correct answer is C: Negative stain. Negative staining uses acidic dyes which are repelled by the bacterial cell wall components, highlighting bacteria with a large amount of peptidoglycan. Acid-fast stain (A) is used to identify Mycobacterium species with waxy cell walls. Gram stain (B) differentiates bacteria into Gram-positive and Gram-negative based on cell wall composition. Option D is a duplicate of option C and is incorrect.

Correct Answer: C

Rationale: The correct answer is C: Negative stain. Negative staining uses acidic dyes which are repelled by the bacterial cell wall components, highlighting bacteria with a large amount of peptidoglycan. Acid-fast stain (A) is used to identify Mycobacterium species with waxy cell walls. Gram stain (B) differentiates bacteria into Gram-positive and Gram-negative based on cell wall composition. Option D is a duplicate of option C and is incorrect.

Correct Answer: D

Rationale: The correct answer is D: Fifth disease. Rubella virus is associated with Fifth disease, also known as erythema infectiosum. It is caused by parvovirus B19, not rubella virus. Mumps (choice A) is caused by the mumps virus. Roseola (choice B) is caused by human herpesvirus 6 or 7. Rubeola (choice C) is the scientific name for measles, caused by the measles virus. Therefore, the correct answer is Fifth disease as it is the disease associated with rubella virus.

Correct Answer: D

Rationale: The correct answer is D: Gram-negative bacteria without peptidoglycan. Chlamydia is an intracellular, gram-negative bacteria that lacks peptidoglycan in its cell wall. Peptidoglycan is a key component of the cell wall in most bacteria, but Chlamydia has a unique structure without it. This makes it different from choices A, B, and C, which describe characteristics not applicable to Chlamydia. Choice A is incorrect because Chlamydia is not a gram-positive coccobacteria. Choice B is incorrect because Chlamydia does have a cell wall, albeit lacking peptidoglycan. Choice C is incorrect because Chlamydia is not a gram-negative bacteria with little peptidoglycan, but rather without it.

Correct Answer: A

Rationale: The correct answer is A: Gram staining. This method is used to differentiate bacteria based on their cell wall composition. In cholera, the causative agent is Vibrio cholerae, which is Gram-negative. By performing Gram staining, the bacteria will appear pink/red under the microscope, confirming the presence of Gram-negative bacteria. Choice B: Neisser's staining is used for staining capsules of bacteria, not suitable for confirming cholera diagnosis. Choice C: Ziehl-Neelsen staining is used for acid-fast bacteria like Mycobacterium tuberculosis, not for confirming cholera diagnosis. Choice D: Burri-Gins staining is not a standard staining method in microbiology and is not relevant for confirming cholera diagnosis.