Which of the following bacteria produce endotoxins?

Correct Answer: C

Rationale: The correct answer is C: Escherichia coli. E. coli is a gram-negative bacterium, which means it has an outer membrane containing lipopolysaccharides (LPS), also known as endotoxins. Endotoxins are released when the bacterium is destroyed, causing an inflammatory response. Streptococcus pneumoniae (choice A) is a gram-positive bacterium and does not produce endotoxins. Clostridium tetani (choice B) produces exotoxins, not endotoxins. Staphylococcus aureus (choice D) is also a gram-positive bacterium and does not produce endotoxins. In summary, E. coli is the correct answer because it is a gram-negative bacterium that produces endotoxins, while the other choices are gram-positive bacteria that do not produce endotoxins.

Correct Answer: B

Rationale: The correct answer is B: Outer membrane with lipopolysaccharides. Gram-negative bacteria have an outer membrane that contains lipopolysaccharides, which play a role in pathogenicity and resistance to certain antibiotics. This outer membrane is a distinguishing feature of Gram-negative bacteria, as opposed to Gram-positive bacteria that have a thick peptidoglycan layer. Choices A, C, and D are incorrect because Gram-negative bacteria have a thin peptidoglycan layer, do have a cell wall (although it is different from Gram-positive bacteria), and do not contain teichoic acids.

Correct Answer: D

Rationale: The correct answer is D because all three bacteria mentioned (Clostridium botulinum, Vibrio cholerae, and Escherichia coli) are capable of producing exotoxins that cause severe diarrhea. Clostridium botulinum produces botulinum toxin leading to botulism, Vibrio cholerae produces cholera toxin causing cholera, and some strains of Escherichia coli produce enterotoxins causing severe diarrhea. Choices A, B, and C alone are incorrect because each of them can produce exotoxins that cause severe diarrhea.

Correct Answer: D

Rationale: The correct answer is D, "All of the above." Clostridium botulinum produces botulinum toxin causing botulism, Vibrio cholerae produces cholera toxin leading to severe diarrhea, and certain strains of Escherichia coli produce toxins causing gastrointestinal illness. Therefore, all three bacteria are known for producing toxins that can cause severe gastrointestinal illness. Choices A, B, and C individually represent bacteria known for producing toxins that can cause severe gastrointestinal illness, making them incorrect individual choices.

Correct Answer: C

Rationale: The normal microflora plays a crucial role in defending against pathogens in the skin and mucus. This is because the skin and mucus act as physical barriers and the normal microflora outcompetes potential pathogens, preventing their colonization. In contrast, the circulatory system (A), hepatobiliary tract (B), and CNS (D) are not typically colonized by normal microflora, so they do not directly contribute to defense against pathogens in those areas.