Medical Microbiology Test Bank

Correct Answer: B

Rationale: The correct answer is B: Salmonellosis. The description of microorganisms resembling a tennis racket indicates the presence of Salmonella typhi, which causes salmonellosis. Salmonella bacteria can appear like tennis rackets under a microscope due to their flagella. Botulism (A) is caused by Clostridium botulinum, which does not resemble a tennis racket. Cholera (C) is caused by Vibrio cholerae, which appears as curved rods under the microscope. Dysentery (D) is usually caused by bacteria like Shigella or Entamoeba histolytica, which do not resemble tennis rackets.

Correct Answer: D

Rationale: The correct answer is D: Pulmonary tuberculosis. The presence of red bacilli stained with Ziehl-Nielsen method indicates acid-fast bacteria, which are characteristic of Mycobacterium tuberculosis, the causative agent of tuberculosis. The size and appearance of the bacilli described match those of M. tuberculosis. Chronic pneumonia, along with the specific staining pattern, strongly suggests tuberculosis as the likely diagnosis. Explanation for other choices: A: Pneumococcal pneumonia is caused by Streptococcus pneumoniae, which would not show red bacilli on Ziehl-Nielsen staining. B: Pulmonary actinomycosis is caused by Actinomyces species, not acid-fast bacteria like M. tuberculosis. C: Pulmonary candidiasis is caused by Candida species, which are fungi and do not appear as red bacilli on staining.

Correct Answer: A

Rationale: The most probable diagnosis is Dermatotropic leishmaniasis. The roundish ulcers, lymph node enlargement, and presence of unicellular aflagellar organisms in discharge are characteristic of this parasitic infection transmitted by sandfly bites. Leishmania parasites cause skin lesions and lymphadenopathy. Toxoplasmosis (B) presents with flu-like symptoms, not ulcers. Scabies (C) causes intense itching and burrows, not ulcers. Trypanosomiasis (D) presents with fever, not ulcers. In this case, the symptoms align closely with Dermatotropic leishmaniasis, making it the most likely diagnosis.

Correct Answer: D

Rationale: The correct answer is D: HIV. HIV is transmitted through direct contact with certain body fluids such as blood, semen, vaginal fluids, and breast milk. This direct contact route of transmission makes it different from the other choices. Salmonellosis is typically transmitted through contaminated food or water (not direct contact). Tularemia is usually transmitted through insect bites or contact with infected animals. Rubella is primarily transmitted through respiratory droplets. Therefore, HIV is the only option with a contact route of transmission.

Correct Answer: D

Rationale: The correct answer is D: Gram-negative coccobacillus. Francisella tularensis is a Gram-negative coccobacillus because it has a unique shape that is between a coccus (spherical) and a bacillus (rod-shaped) and it stains pink/red in the Gram staining process. It is important to note that it is not a coccus (choice B) or a Gram-positive bacterium (choice A). Choice C is too general and does not specify the coccobacillus shape of F. tularensis. So, the correct answer is D due to its specific characteristics as a Gram-negative coccobacillus.