Correct Answer: C

Rationale: The correct answer is C: Erysipelas. Erysipelas is a type of acute infection caused by group A Streptococcus bacteria. This bacteria infects the upper dermis and superficial lymphatics, leading to a distinct raised, well-demarcated, erythematous skin lesion. The other choices are incorrect because: A Carbuncle is a deep skin infection involving hair follicles, B Impetigo is a superficial skin infection caused by Staphylococcus or Streptococcus bacteria, and D Acne is a chronic inflammatory skin condition not typically caused by group A Streptococcus.

Correct Answer: A

Rationale: The correct method of laboratory diagnostics for suspected malaria is blood examination. Malaria is diagnosed by detecting the presence of the Plasmodium parasite in the patient's blood. This can be done through microscopy to identify the parasite in a blood smear or through rapid diagnostic tests (RDTs) that detect specific antigens produced by the parasite. Blood examination allows for the direct visualization of the parasite, making it the most accurate method for diagnosing malaria. Immunological tests, stool examination, and urine examination are not suitable for diagnosing malaria as the parasite primarily resides in the red blood cells. Stool and urine examinations are more commonly used for diagnosing gastrointestinal or urinary tract infections, respectively.

Correct Answer: A

Rationale: The correct answer is A: Candida fungi. In the context of a 70-year-old man with angular cheilitis (lesion at the corners of the mouth) and stomatitis, the presence of large ovoid gram-positive cells points towards Candida species, which are yeast fungi. Candida is a common opportunistic pathogen that can cause oral thrush and angular cheilitis in immunocompromised individuals, such as elderly people. Candida fungi are known to appear as large ovoid cells under microscopic examination. Summary of other choices: B: Streptococci are gram-positive bacteria and are not typically associated with large ovoid cells seen in this case. C: Staphylococci are also gram-positive bacteria and are not known to present as large ovoid cells in this context. D: Neisseria are gram-negative bacteria and are not the usual etiological agents for oral lesions like angular cheilitis.

Correct Answer: A

Rationale: The correct answer is A: The polysaccharide capsule. The capsule of Neisseria meningitidis plays a crucial role in its virulence by preventing phagocytosis, allowing the bacteria to evade the host's immune system. This leads to increased survival and colonization in the host. Choice B: The beta lactamase is incorrect because it is an enzyme that breaks down beta-lactam antibiotics and does not directly contribute to the virulence of Neisseria meningitidis. Choice C: The erythrogenic toxin is incorrect as this toxin is produced by Streptococcus pyogenes, not Neisseria meningitidis. Choice D: None of the above is incorrect as the polysaccharide capsule is indeed a key virulence factor of Neisseria meningitidis.

Correct Answer: B

Rationale: The correct answer is B: Pseudomonas aeruginosa. This bacterium is commonly associated with hospital-acquired infections due to its ability to survive in hospital environments, resist antibiotics, and infect immunocompromised patients. Streptococcus pneumoniae (choice A) is more commonly associated with community-acquired pneumonia. Vibrio cholerae (choice C) causes cholera, a waterborne disease, and is not typically associated with hospital-acquired infections. Choice D is incorrect because Pseudomonas aeruginosa is indeed associated with hospital-acquired infections.