Which bacteria produce exotoxins that damage host tissues?

Correct Answer: A

Rationale: The correct answer is A: Clostridium tetani and Bacillus anthracis. Both bacteria produce exotoxins that damage host tissues. Clostridium tetani produces tetanospasmin, which causes muscle rigidity in tetanus. Bacillus anthracis produces anthrax toxins, leading to tissue damage and systemic effects. Explanation: - Choice B (Escherichia coli and Pseudomonas aeruginosa) primarily cause infections through other mechanisms and do not produce exotoxins that damage host tissues. - Choice C (Streptococcus pneumoniae and Listeria monocytogenes) are known for causing infections but not primarily through exotoxins that damage host tissues. - Choice D (Salmonella typhi and Mycobacterium tuberculosis) cause diseases through different mechanisms and do not produce exotoxins that directly damage host tissues.

Correct Answer: D

Rationale: The correct answer is D, Late congenital syphilis. This is because the patient presents with Hutchinson's teeth, which are a characteristic feature of late congenital syphilis. Hutchinson's teeth are small, barrel-shaped teeth with a wider cervix and notched incisors. The patient's history of visual impairment and hearing aid use also support the diagnosis of late congenital syphilis, as these are common manifestations of this stage of the disease. Choice A, Primary syphilis, is incorrect because it typically presents with a painless sore at the site of infection, not dental abnormalities. Choice B, Early congenital syphilis, is incorrect as dental abnormalities in this stage are usually more severe, such as mulberry molars. Choice C, Neurosyphilis, is incorrect as it primarily affects the central nervous system and does not typically present with dental abnormalities.

Correct Answer: A

Rationale: The correct answer is A: Ziehl-Neelsen staining method was applied. 1. Ziehl's solution is used as a primary stain in Ziehl-Neelsen staining for acid-fast organisms like Mycobacterium tuberculosis. 2. Sulfuric acid is used as a decolorizer to remove excess stain. 3. Methylene blue is not part of the Ziehl-Neelsen staining method. 4. Burri's, Gram's, and Peshkov's staining methods are not used for acid-fast staining.

Correct Answer: B

Rationale: The correct answer is B: Mycelium. Mycelium refers to the network of branching filaments that form the main body of a fungus. When fungi grow on solid media, they develop a visible mass of mycelium. Hyphae (A) are the individual filaments that make up mycelium. Spores (C) are reproductive cells produced by fungi. Columella (D) refers to a specialized structure found in some fungi but is not related to the colonies grown on solid media. Therefore, the correct term for the colonies of fungi on solid media is mycelium.

Correct Answer: B

Rationale: The correct answer is B because the nucleocapsid of viruses is composed of the genome (genetic material) and the capsid (protein coat). The genome contains the viral genetic information, while the capsid protects the genome and helps in viral attachment and entry into host cells. Choice A is incorrect because the envelope is not part of the nucleocapsid but surrounds the capsid in some viruses. Choice C is incorrect as spikes are surface proteins on the viral envelope, not part of the nucleocapsid. Choice D is also incorrect because the envelope is external to the capsid and genome in many viruses.

Correct Answer: A

Rationale: The correct answer is A: Tinned food. Botulism is often caused by the botulinum toxin produced by the bacterium Clostridium botulinum, which can be present in improperly canned foods. Analyzing tinned food allows for direct detection of the toxin or bacteria, confirming the diagnosis. Potatoes, pasteurized milk, and boiled meat are less likely sources of botulism compared to tinned food, making them less suitable for initial analysis in this case.

Correct Answer: A

Rationale: The presence of acid-fast bacilli stained red against a blue background indicates mycobacteria, specifically Mycobacterium tuberculosis in this case. Ziehl-Neelsen staining is commonly used to detect tuberculosis. Diphtheria is caused by Corynebacterium diphtheriae, which does not stain with Ziehl-Neelsen. Pneumonia is a general term for lung infections caused by various pathogens. Leprosy is caused by Mycobacterium leprae, which requires special staining methods different from Ziehl-Neelsen.

Correct Answer: C

Rationale: The correct answer is C: beaded. In an agar slant, beaded colonies appear as separate or semiconfluent, forming small, round colonies with gaps between them. This term accurately describes the appearance of the colonies in this context. A: Filiform colonies are dense and opaque with smooth edges, not separate or semiconfluent. B: Echinulate colonies have spiny projections, not the characteristic of separate or semiconfluent growth. D: Effuse colonies spread out extensively and lack defined borders, unlike the distinct appearance of separate or semiconfluent colonies.

Correct Answer: A

Rationale: The correct answer is A: Lysozyme. Lysozyme is an enzyme that targets and breaks down the peptidoglycan in bacterial cell walls by cleaving the glycosidic bonds between the sugar components. This action weakens the cell wall, leading to bacterial cell lysis. Amylase (B) breaks down starch, not peptidoglycan. Protease (C) breaks down proteins, not peptidoglycan. Lipase (D) breaks down lipids, not peptidoglycan. Therefore, Lysozyme is the correct enzyme for breaking down peptidoglycan in bacterial cell walls.