Examination of a child revealed some whitish spots looking like coagulated milk on the mucous membrane of his cheeks and tongue. Analysis of smears revealed gram-positive oval yeast-like cells. What causative agents are they?

Correct Answer: A

Rationale: The correct answer is A: Candida. The whitish spots resembling coagulated milk on the mucous membranes are characteristic of oral thrush, a condition caused by Candida species. Candida is a gram-positive oval yeast-like fungus commonly found in the oral cavity. Staphylococci (B) are gram-positive cocci, not yeast-like cells. Diphtheria bacillus (C) causes diphtheria, not oral thrush. Actinomycetes (D) are filamentous bacteria, not yeast-like cells typically seen in oral thrush. Therefore, A is the correct answer based on the clinical presentation and microscopic findings.

Correct Answer: A

Rationale: The correct answer is A because it accurately describes the major morphological forms of bacteria. Cocci are spherical, rod-shaped bacteria are called bacilli, and curved bacteria are spirilla. Staphylococci, streptococci, and diplococci are specific types of cocci, not major morphological forms. Basicili and spiralis are not common morphological forms of bacteria. Option D is incorrect as the other choices do represent major morphological forms of bacteria.

Correct Answer: D

Rationale: The correct answer is D. Escherichia coli, Salmonella enterica, and Pseudomonas aeruginosa all produce endotoxins that can lead to septic shock. Endotoxins are components of the outer membrane of Gram-negative bacteria that can trigger a systemic inflammatory response, potentially leading to septic shock. E. coli and Salmonella are common causes of bacterial infections that can result in septic shock, while P. aeruginosa is known for causing infections in immunocompromised individuals. Therefore, since all three bacteria produce endotoxins that can lead to septic shock, the correct answer is D.Choices A, B, and C are incorrect because each of these bacteria individually produces endotoxins that can contribute to septic shock.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Gram-positive diplococci with pointed ends indicate Streptococcus pneumoniae. 2. Presence of capsules supports the likelihood of S. pneumoniae. 3. S. pneumoniae is a common cause of pneumonia. 4. Klebsiella pneumoniae is Gram-negative and does not form diplococci. 5. Neisseria meningitidis typically causes meningitis, not pneumonia. 6. Staphylococcus aureus is Gram-positive but does not typically present as diplococci in pneumonia cases.

Correct Answer: A

Rationale: Step 1: Ziehl-Neelsen staining is a type of acid-fast staining used to detect acid-resistant bacteria like Mycobacterium species. Step 2: Acid-resistant bacteria have a high lipid content in their cell walls, making them resist decolorization with acid-alcohol. Step 3: Mycobacterium species, such as M. tuberculosis and M. leprae, are examples of acid-resistant bacteria. Step 4: Spores are not typically stained using Ziehl-Neelsen staining, making choice B incorrect. Step 5: Metachromatic bodies are stained using specific techniques like Albert's stain, not Ziehl-Neelsen staining, making choice C incorrect. Summary: Ziehl-Neelsen staining is specifically used for acid-resistant bacteria detection, making choice A the correct answer. Choices B and C are incorrect as they do not align with the purpose of Ziehl-Neelsen staining. Choice D is incorrect as Ziehl

Correct Answer: A

Rationale: The correct answer is A: Toxoplasma. Toxoplasma gondii is a protozoan parasite that can infect the brain and cause vision loss. The description of half-moon-shaped organisms with a pointed end matches the appearance of Toxoplasma under the microscope. Toxoplasma is known to cause a condition called toxoplasmosis, which can lead to neurological symptoms such as vision loss. Leishmania, Lamblia, Amoeba, and Trichomonad are not known to cause brain infections or vision loss, making them incorrect choices.

Correct Answer: B

Rationale: The correct answer is B: cytopathic effect. When viruses infect cell cultures, they induce degenerative changes known as cytopathic effects, which include cell shrinkage, rounding, detachment, and cell death. This term specifically refers to the damage caused by viral replication within the cells. A: Cytolytic effect refers to the destruction of cells by viruses, which is a more specific type of cytopathic effect involving cell lysis. C: Cytotoxic effect typically refers to the toxic effects of substances on cells, not specifically related to viral propagation. D: The statement that all three answers are correct is incorrect as only option B accurately describes the degenerative changes resulting from viral propagation in infected cell cultures.

Correct Answer: B

Rationale: The correct answer is B, Antony van Leeuwenhoek. He was the first to observe and describe "animalcules" (microorganisms) through his early microscopes. Robert Hooke (A) is known for his work with cells but did not discover animalcules. Hans Janssen (C) and John Needham (D) did not make significant contributions to the discovery of microorganisms. Leeuwenhoek's pioneering observations were crucial in the development of microbiology.

Correct Answer: C

Rationale: The correct answer is C: Escherichia coli. E. coli is the most common cause of acute cystitis. It typically presents with leukocytes and gram-negative bacilli in the urine. The green pigment production indicates pyocyanin, which is a characteristic of E. coli. Pseudomonas aeruginosa (A) can also produce green pigment, but it is less common in urinary tract infections. Proteus mirabilis (B) is associated with a swarming motility pattern on agar, not mucous colonies. Klebsiella pneumoniae (D) is associated with pneumonia and other respiratory infections, not cystitis.