Which type of bacteria have an outer membrane containing lipopolysaccharides (LPS)?

Correct Answer: B

Rationale: The correct answer is B: Gram-negative bacteria. Gram-negative bacteria have an outer membrane containing lipopolysaccharides (LPS). In the Gram staining technique, these bacteria appear pink/red due to the thin peptidoglycan layer, which allows the crystal violet stain to be washed out, revealing the safranin counterstain. Gram-positive bacteria (choice A) have a thick peptidoglycan layer but lack an outer membrane with LPS. Choice C is incorrect since only Gram-negative bacteria possess LPS in their outer membrane. Choice D is incorrect as all bacteria can be classified as either Gram-positive or Gram-negative based on their cell wall structure.

Correct Answer: A

Rationale: The correct answer is A: Clostridium perfringens. This bacterium is an anaerobic, Gram-positive rod that forms terminal spores and produces gas. It is commonly associated with wound infections and gas gangrene. Clostridium botulinum causes botulism and does not typically present with gas production. Bacillus anthracis is an aerobic, Gram-positive spore-forming bacterium causing anthrax. Clostridium tetani causes tetanus and does not produce gas. Thus, based on the characteristics described in the question, Clostridium perfringens is the most likely causative agent.

Correct Answer: C

Rationale: The correct answer is C: urethra. Resident microflora refers to the normal, beneficial bacteria that inhabit a specific area of the body without causing harm. The urethra is one of the locations where resident microflora are commonly found. These bacteria play a vital role in maintaining a healthy balance and preventing harmful pathogens from colonizing the urethra. Blood (A), lung (B), and cerebro-spinal fluid (D) are not typical locations for resident microflora as these areas are usually sterile or have very limited microbial presence to prevent infections.

Correct Answer: C

Rationale: Rationale: Metronidazole is the drug of choice for systemic amebiasis due to its high efficacy against Entamoeba histolytica. It has good tissue penetration and can treat intestinal, liver, and lung involvement. Quiniofone (A) has limited use and is not recommended for amebiasis. Enteroseptol (B) is not effective against systemic amebiasis. Tetracycline (D) is not the first-line treatment for amebiasis and has limited efficacy against Entamoeba histolytica.

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. The presence of Gram-positive cocci in pairs with a capsule is characteristic of Streptococcus pneumoniae. Step 1: Gram-positive cocci in pairs indicate a Streptococcus species. Step 2: The presence of a capsule suggests S. pneumoniae specifically. Summary: B: Staphylococcus aureus is a Gram-positive cocci but does not typically present in pairs with a capsule. C: Neisseria gonorrhoeae is a Gram-negative diplococcus, not a Gram-positive cocci. D: Klebsiella pneumoniae is a Gram-negative rod, not a cocci.

Correct Answer: D

Rationale: Interferon delta is not a known type of interferon, making choice D incorrect. Interferon beta is indeed produced by fibroblasts (choice A), interferon alpha by leukocytes (choice B), and interferon gamma by lymphocytes (choice C). Each type of interferon is produced by specific cells in the immune system, contributing to the body's defense against viruses and other pathogens.

Correct Answer: A

Rationale: The correct answer is A: Giardia lamblia. Giardia lamblia is a protozoan parasite that causes foul-smelling diarrhea. The trophozoites of Giardia lamblia have two nuclei and flagella, which are characteristic features seen on stool microscopy. The presence of these specific features helps differentiate Giardia lamblia from the other options. Entamoeba histolytica (B) typically presents with one nucleus and lacks flagella. Trichomonas vaginalis (C) is a sexually transmitted parasite with a different morphology. Balantidium coli (D) is a ciliated parasite, not flagellated like Giardia lamblia.

Correct Answer: A

Rationale: The correct answer is A: Clostridium botulinum. This bacterium produces the neurotoxin responsible for botulism. Clostridium perfringens is associated with gas gangrene, not botulism. Streptococcus pneumoniae causes pneumonia, and Neisseria gonorrhoeae causes gonorrhea, not botulism. Therefore, A is the correct choice.

Correct Answer: B

Rationale: The correct answer is B: cell wall. Lysozyme is an enzyme that targets the cell wall of bacteria by breaking down the peptidoglycan layer, leading to bacterial cell lysis. This action disrupts the structural integrity of the bacteria, ultimately causing their death. Choices A, C, and D are incorrect because lysozyme does not target the cytoplasm, nucleus, or capsule of bacteria. The primary function of lysozyme is to act on the cell wall, making option B the correct answer in this context.