A 16-year-old boy from the rural area entered the technical school. During a regular Mantoux test, it turned out that this boy had a negative reaction. What tactics should the doctor choose as the most rational in this case?

Correct Answer: D

Rationale: The correct answer is D: BCG vaccination. BCG vaccination is recommended for individuals with a negative Mantoux test result, especially in countries where tuberculosis is prevalent. This vaccination can help provide protection against tuberculosis. Choice A is incorrect because repeating the Mantoux test in a month is unnecessary since the boy already had a negative reaction. Choice B is incorrect as serodiagnosis of tuberculosis is not the first-line approach for diagnosis, especially in this scenario. Choice C is incorrect because urgent isolation is not necessary based solely on the Mantoux test result. Isolation is typically reserved for individuals with active tuberculosis.

Correct Answer: A

Rationale: The correct answer is A: Synthesize proteins. Bacterial ribosomes are responsible for translating mRNA into proteins through a process called translation. Ribosomes do not generate ATP (choice B), produce DNA (choice C), or synthesize lipids (choice D). These processes are carried out by other cellular components such as mitochondria for ATP production, DNA polymerase for DNA replication, and enzymes for lipid synthesis. The primary function of bacterial ribosomes is protein synthesis, making choice A the correct answer.

Correct Answer: C

Rationale: The correct answer is C: Macrolides or fluoroquinolones. Legionella pneumophila is a bacterium that causes Legionnaires' disease, a severe form of pneumonia. Macrolides (like azithromycin) and fluoroquinolones (like levofloxacin) are the recommended first-line treatments due to their ability to penetrate into lung tissues where Legionella infects. Penicillins and cephalosporins (choice A) are not effective against Legionella as it is intracellular and resistant to these antibiotics. Ethambutol and isoniazid (choice B) are used to treat tuberculosis, not Legionella infections. Second and third generation cephalosporins (choice D) are also not effective against Legionella. Therefore, the best choice for treating Legionella pneumophila infections is macrolides or fluoroquinolones.

Correct Answer: B

Rationale: The correct answer is B: protomeres. Viral capsomeres are the building blocks of viral capsids, which are protein coats that enclose and protect the viral genetic material. These capsomeres are made up of smaller subunits called protomeres. Envelopes (A) refer to a lipid membrane surrounding some viruses, not the subunits of capsomeres. Capsids (C) are the protein coats that capsomeres make up, not the subunits themselves. Nucleoids (D) are found in bacterial cells and refer to the region where the genetic material is located, not the subunits of viral capsomeres.

Correct Answer: B

Rationale: The correct answer is B: IgM. IgM antibodies are the first type of antibodies produced in response to an infection, indicating an active or recent infection. In the case of a rubella virus infection in a fetus, IgM antibodies can be detected in the umbilical cord blood, confirming the presence of the virus. IgA antibodies are mainly found in mucosal areas, IgG antibodies indicate past infection or immunity, and IgD antibodies play a role in B cell activation but are not typically detected in this context.

Correct Answer: A

Rationale: The most probable diagnosis is A: Malaria. The patient's symptoms of periodic chills, high fever, and profuse sweating, along with living in Africa where malaria is endemic, strongly suggest malaria. The enlarged liver and spleen are consistent with malaria infection. The low erythrocyte count indicates hemolysis, a common feature of malaria. Spotted fever and sepsis do not typically present with the same pattern of symptoms and travel history as seen in this case. Haemolytic anaemia would not explain the patient's fever episodes and other symptoms. Therefore, based on the symptoms, travel history, and laboratory findings, malaria is the most likely diagnosis.

Correct Answer: B

Rationale: The correct answer is B: Uptake of naked DNA from the environment. Bacterial transformation is a process where bacteria take up free DNA from their surroundings and incorporate it into their own genome. This process is essential for genetic recombination and the acquisition of new traits. Plasmids are small DNA molecules that can be transferred between bacteria, but not necessarily through pili. Bacteriophages are viruses that infect bacteria and transfer their DNA, but this is not the primary mechanism of bacterial transformation. Binary fission is a method of bacterial reproduction, not related to the uptake of DNA.

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: 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.