The causative agent of botulism causes severe food poisoning. Specify the most characteristic morphological feature of botulism causative agent:

Correct Answer: D

Rationale: The correct answer is D: Thin mobile bacillus with central spore. This is because the causative agent of botulism, Clostridium botulinum, is a gram-positive bacillus that typically appears as a thin rod-shaped bacterium with a central endospore. This characteristic morphology is essential in the identification of Clostridium botulinum. A: Gram-positive bacillus with subterminal spore - This is incorrect as Clostridium botulinum typically has a central endospore, not a subterminal one. B: Thick gram-positive non-spore-forming bacillus - This is incorrect as Clostridium botulinum forms endospores, although they are not thick. C: Gram-positive bacillus with terminal spore - This is incorrect as the spore of Clostridium botulinum is typically central, not terminal.

Correct Answer: A

Rationale: The correct answer is A: Lipopolysaccharides. Endotoxins are a type of bacterial toxin found in the outer membrane of Gram-negative bacteria. They consist of lipid A, which is a lipid component, and polysaccharides, making them lipopolysaccharides. Lipoproteins (choice B) and glycoproteins (choice C) do not accurately describe the chemical structure of endotoxins. "None of the above" (choice D) is incorrect as lipopolysaccharides are indeed the chemical structure of endotoxins.

Correct Answer: A

Rationale: The correct answer is A: TRUE. Poxviruses are indeed the largest viruses known, ranging from 200-450 nm in size, which is close to the resolution limit of a light microscope. This makes them almost visible under a light microscope. Explanation: 1. Poxviruses have complex structures and are among the largest viruses. 2. Light microscopes have a resolution limit of around 200 nm. 3. Poxviruses fall within the size range that is close to the resolution limit of a light microscope. 4. Therefore, poxviruses are almost visible under a light microscope. Summary: Choice B is incorrect because poxviruses are indeed large enough to be almost visible under a light microscope. Choice C is incorrect as it implies uncertainty, but poxviruses are consistently close to the resolution limit of a light microscope. Choice D is incorrect as the size of poxviruses being almost visible under a light microscope is a factual statement, not dependent

Correct Answer: A

Rationale: The correct answer is A: Vibrio cholerae. 1. Vibrio cholerae is a Gram-negative, comma-shaped bacterium known to cause cholera. 2. Shigella dysenteriae causes dysentery, not cholera. 3. Salmonella typhi causes typhoid fever, not cholera. 4. Campylobacter jejuni causes gastroenteritis, not cholera. Therefore, based on the symptoms presented and the characteristics of the bacterium, Vibrio cholerae is the most likely microorganism.

Correct Answer: A

Rationale: The correct answer is A: Escherichia coli. E. coli is the most common bacteria responsible for causing urinary tract infections due to its ability to adhere to the urinary tract lining and multiply rapidly. It is a normal inhabitant of the gut and can enter the urinary tract through improper hygiene practices. Salmonella enterica and Neisseria gonorrhoeae are typically associated with other infections like food poisoning and gonorrhea, respectively. Mycobacterium tuberculosis causes tuberculosis, not urinary tract infections. Thus, based on its prevalence and pathogenicity in the urinary tract, E. coli is the correct choice.

Correct Answer: A

Rationale: The correct answer is A: Metronidazole. It is the drug of choice for treating systemic amebiasis due to its high efficacy against Entamoeba histolytica. Metronidazole is well-absorbed, reaches therapeutic levels in the intestines, liver, and lungs, making it effective in treating the multi-organ involvement in this case. Choice B: Quiniofone is not a recommended treatment for amebiasis. Choice C: Tetracycline is not the first-line treatment for systemic amebiasis. Choice D: Quingamine is not a recognized drug for treating amebiasis.

Correct Answer: B

Rationale: The correct answer is B (Urethra). Resident microflora are typically found in various parts of the body where they establish a stable population without causing harm. The urethra is one of the locations where resident microflora are commonly present, helping to maintain a healthy microbial balance and prevent pathogenic bacteria from colonizing the area. In contrast, choices A, C, and D are not typical locations for resident microflora. Blood is normally sterile, the lungs have a different microbial environment due to their exposure to the external environment, and the cerebro-spinal fluid is also typically sterile to prevent infections in the central nervous system.

Correct Answer: B

Rationale: The correct answer is B: BCG vaccine. Bacille Calmette-Guérin (BCG) vaccine is used to prevent tuberculosis, which is caused by a bacterium related to anthrax. BCG vaccine can provide cross-protection against anthrax due to its similar mechanisms of action. STI live vaccine (choice A) is used for sexually transmitted infections, not anthrax. Salk vaccine (choice C) is used for polio, and Sabin's vaccine (choice D) is also for polio, not anthrax. Therefore, BCG vaccine is the most appropriate choice for preventing the spread of anthrax among animals in the countryside.

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium appears as purple-stained diplococci with pointed ends on Gram staining. S. pneumoniae is a common cause of pneumonia. It is encapsulated and has a lancet-shaped appearance, which is characteristic of the pointed ends seen in the staining. Staphylococcus aureus (B) typically appears as clusters of gram-positive cocci, not diplococci. Klebsiella pneumoniae (C) is a gram-negative rod, not a diplococci. Neisseria meningitidis (D) is a gram-negative diplococci but typically lacks the pointed ends seen in the staining of S. pneumoniae.