Which of the following is a key feature of Mycobacterium tuberculosis?

Correct Answer: C

Rationale: The correct answer is C: Acid-fast cell wall. Mycobacterium tuberculosis is characterized by its unique cell wall composition, containing high levels of mycolic acids which make it acid-fast. This property allows it to resist decolorization during acid-fast staining procedures. This distinguishes it from other bacteria. A: Producing spores is not a key feature of Mycobacterium tuberculosis. Spore formation is more commonly associated with bacterial species such as Bacillus and Clostridium. B: Mycobacterium tuberculosis is not Gram-negative. It is classified as acid-fast Gram-positive. D: Mycobacterium tuberculosis does not produce toxins as a key feature. Its pathogenicity is more closely related to its ability to evade host immune responses and persist in host tissues.

Correct Answer: B

Rationale: The correct answer is B: Gram negative coccobacillus. Bordetella pertussis, the causative agent of pertussis, is a gram-negative coccobacillus. This is because it is a small, rod-shaped bacterium that appears both as a bacillus (rod-shaped) and a coccus (spherical) shape. It does not retain the crystal violet stain in the Gram staining process, indicating its negative gram nature. Choice A is incorrect because pertussis is not a gram-positive bacillus. Choice C is incorrect because pertussis is not a long gram-negative rod-shaped bacterium. Choice D is incorrect as the other options do not accurately describe the morphology of Bordetella pertussis.

Correct Answer: D

Rationale: The correct answer is D because antigens can be composed of lipids, proteins, or polysaccharides. Antigens are molecules that can elicit an immune response in the body. They can be diverse in their chemical composition, leading to the recognition and response by the immune system. Therefore, the correct choice is D as antigens can be any of these chemical components. Choices A, B, and C are incorrect because they each represent a possible chemical composition of antigens, but the flexibility of antigens to be made up of any of these components makes D the most accurate choice.

Correct Answer: A

Rationale: The correct answer is A: Anthrax. The symptoms of fever, headache, weakness, and the skin lesion described (hyperemic with a dark red infiltration, black center, and pustules) are characteristic of cutaneous anthrax. The black center is known as an eschar. Anthrax is caused by the bacterium Bacillus anthracis, commonly found in cattle. Plague (choice B) typically presents with swollen lymph nodes (buboes) and is caused by Yersinia pestis. Tularemia (choice C) presents with fever, ulcer at the site of infection, and lymphadenopathy, caused by Francisella tularensis. Furuncle (choice D) is a localized skin infection typically caused by Staphylococcus aureus, presenting as a red, swollen, and painful bump.

Correct Answer: A

Rationale: The correct answer is A because in the lytic cycle, the bacteriophage destroys the host cell upon release, whereas in the lysogenic cycle, the phage integrates its DNA into the host genome without killing the host immediately. This integration may lead to the destruction of the host cell at a later stage. Choice B is incorrect as lytic phages do destroy the host cell. Choice C is incorrect as the two cycles have distinct mechanisms. Choice D is incorrect as there are clear differences between the lytic and lysogenic cycles.

Correct Answer: B

Rationale: The correct answer is B: BKV. BK virus can cause hemorrhagic cystitis in immunocompromised patients by infecting the urinary tract. It primarily affects the renal tubular epithelial cells, leading to hemorrhagic cystitis. EBV (A) causes infectious mononucleosis, HSV1 (C) causes oral and genital herpes, and JCV (D) causes progressive multifocal leukoencephalopathy, none of which are associated with hemorrhagic cystitis.

Correct Answer: C

Rationale: The correct answer is C: Tularemia. Ticks can transmit tularemia, a bacterial infection caused by Francisella tularensis. Ticks pick up the bacteria when feeding on infected animals and can then transmit it to humans through their bites. Botulism (A) is caused by toxins produced by Clostridium botulinum bacteria, not transmitted by ticks. Anthrax (B) is a bacterial infection caused by Bacillus anthracis, typically transmitted through contact with contaminated animal products. MRSA (D) is a bacterial infection caused by Staphylococcus aureus, commonly transmitted through direct contact with infected individuals or contaminated surfaces, not by ticks.

Correct Answer: A

Rationale: The correct answer is A: Bacterial DNA. PCR analysis detects specific DNA sequences, so a positive result for H. pylori indicates the presence of the bacterial DNA in the gastric biopsy specimen. This method identifies the genetic material of the bacterium, not the bacterium itself (choice C) or its toxins (choice B). Additionally, PCR does not directly detect bacterial enzymes (choice D) but rather focuses on genetic material for accurate identification. Therefore, in this case, the detection of H. pylori in the PCR analysis points to the presence of bacterial DNA, confirming the etiology of peptic ulcer disease.

Correct Answer: B

Rationale: The correct answer is B: Motility. Bacterial flagella function in providing motility to bacteria, allowing them to move towards nutrients or away from harmful substances. Flagella are long, whip-like appendages that rotate to propel the bacteria through their environment. Incorrect choices: A: Protein synthesis - Bacterial flagella are not involved in protein synthesis. C: Adhesion to surfaces - While some bacteria use flagella for attachment, their main function is not adhesion. D: DNA replication - Flagella do not play a role in DNA replication, which occurs in the bacterial cell's nucleus.