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: Giardia lamblia. This protozoan matches the description of the causative agent because it has two nuclei, four flagella, and a ventral adhesive disc. Giardia lamblia is commonly found in the duodenum and causes giardiasis. The other choices can be eliminated because Leishmania donovani causes visceral leishmaniasis, not the described symptoms. Entamoeba coli is a non-pathogenic amoeba found in the large intestine. Trypanosoma gambiense causes African trypanosomiasis and is transmitted by the tsetse fly, not matching the described characteristics.

Correct Answer: B

Rationale: The correct answer is B: Borrelia burgdorferi. Borrelia burgdorferi is the bacteria responsible for causing Lyme disease. It is transmitted to humans through the bite of infected black-legged ticks. Treponema pallidum causes syphilis, Leptospira interrogans causes leptospirosis, and Rickettsia rickettsii causes Rocky Mountain spotted fever. Borrelia burgdorferi is specifically associated with Lyme disease due to its transmission through tick bites and the characteristic symptoms it causes.

Correct Answer: A

Rationale: The correct answer is A: Bacillus anthracis. The black, painless carbuncle with peripheral vesicular rash is characteristic of cutaneous anthrax. Microscopy showing non-motile Gram-positive rods with a capsule aligns with Bacillus anthracis. The other choices can be eliminated: B: Staphylococcus aureus does not typically form a black lesion or have a capsule. C: Clostridium perfringens causes gas gangrene, not the described lesion. D: Bacillus subtilis is not associated with the specific clinical presentation mentioned.

Correct Answer: C

Rationale: The correct answer is C: beaded. In an agar slant, beaded colonies appear as separate or semiconfluent, forming small, round colonies with gaps between them. This term accurately describes the appearance of the colonies in this context. A: Filiform colonies are dense and opaque with smooth edges, not separate or semiconfluent. B: Echinulate colonies have spiny projections, not the characteristic of separate or semiconfluent growth. D: Effuse colonies spread out extensively and lack defined borders, unlike the distinct appearance of separate or semiconfluent colonies.

Correct Answer: A

Rationale: Step 1: Gram-negative bacillus indicates P. aeruginosa, known for causing wound infections. Step 2: Semi-transparent mucous colonies of blue-green color with a pearlescent appearance are characteristic of P. aeruginosa. Step 3: Specific odor of violets or jasmine is a unique feature of P. aeruginosa. Therefore, the correct answer is A: P. aeruginosa. Summary: - B: P. vulgaris typically forms yellow colonies and doesn't have the characteristic odor. - C: S. aureus forms creamy white colonies, not blue-green, and has a distinct odor. - D: S. pyogenes forms grayish-white colonies and doesn't have the unique characteristics described.

Correct Answer: A

Rationale: The correct answer is A: HSV-1. Herpes simplex infections on lips and in the mouth are most commonly caused by HSV-1 due to its preference for infecting oral mucosa. HSV-2 typically causes genital herpes. HSV-6 and HSV-7 are less common and not typically associated with oral infections. Therefore, based on the typical presentation and epidemiology of herpes simplex infections, HSV-1 is the most likely cause in this scenario.

Correct Answer: D

Rationale: The correct answer is D: Positive strand RNA viruses. These viruses have RNA genomes that can be directly translated by host ribosomes without the need for transcription. In contrast, single-strand DNA and double-strand DNA viruses require transcription to generate mRNA for translation. Choice A is incorrect as there is a correct answer. Choice B and C are incorrect because both single-strand DNA and double-strand DNA viruses require transcription for mRNA synthesis.

Correct Answer: A

Rationale: The correct answer is A: Anaerobic infection. The sudden deterioration, bursting pain, edema, foul appearance of wound, and presence of gas are indicative of gas gangrene caused by anaerobic bacteria like Clostridium perfringens. These bacteria thrive in low oxygen environments, such as deep wound tissues. The symptoms align with the classic presentation of gas gangrene, necessitating immediate surgical intervention. Choice B: Aerobic gram-negative, is incorrect because anaerobic bacteria, not aerobic gram-negative bacteria, are responsible for gas gangrene. Choice C: Putrid, is incorrect as it is a general term referring to foul-smelling decay and does not specify the type of infection. Choice D: Aerobic gram-positive, is incorrect as gas gangrene is typically caused by anaerobic bacteria, not aerobic gram-positive bacteria.