A 25-year-old patient was delivered to an infectious diseases unit on the 3rd day of illness with complaints of headache, pain in lumbar spine and gastrocnemius muscles, high fever, chill. Objectively: condition of moderate severity. Scleras are icteric. Pharynx is hyperemic. Tongue is dry with dry brown coating. Abdomen is distended. Liver is enlarged by 2 cm. Spleen is not enlarged. Palpation of muscles, especially gastrocnemius muscles, is painful. Urine is dark in color. Stool is normal in color. The most likely diagnosis is:

Correct Answer: A

Rationale: The correct diagnosis is Leptospirosis. Leptospirosis presents with headache, fever, muscle pain, jaundice, and kidney involvement. The patient's symptoms of headache, lumbar and muscle pain, high fever, icteric scleras, and dark urine are classic for Leptospirosis. The enlarged liver could be due to liver involvement in the disease. The absence of splenic enlargement and normal stool color rule out malaria. Infectious mononucleosis typically presents with sore throat and lymphadenopathy, which are absent in this case. Viral hepatitis A may present with similar symptoms, but the presence of muscle pain and dark urine is more indicative of Leptospirosis. Therefore, based on the patient's symptoms and clinical findings, Leptospirosis is the most likely diagnosis.

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pyogenes. This bacterium is known to cause sore throat and fever, commonly referred to as strep throat. Gram's stain showing Gram-positive cocci in chains is characteristic of Streptococcus species. Streptococcus pyogenes is a beta-hemolytic bacterium that forms chains and is a common cause of bacterial pharyngitis. Staphylococcus aureus (B) is a Gram-positive cocci that forms clusters, not chains. Neisseria gonorrhoeae (C) is a Gram-negative diplococcus and is not associated with sore throat. Enterococcus faecalis (D) is a Gram-positive cocci that can cause infections but is not typically associated with sore throat.

Correct Answer: B

Rationale: The correct answer is B: Herpangina. Coxsackie Viruses are known to cause Herpangina, which is characterized by sore throat, fever, and painful blisters in the mouth and throat. This is because Coxsackie Viruses typically infect the throat and mouth mucosa. Hemorrhagic conjunctivitis (A) is commonly caused by Adenoviruses, not Coxsackie Viruses. Mumps (C) is caused by the Mumps virus, a completely different virus. Poliomyelitis (D) is caused by the Poliovirus, not Coxsackie Viruses. Therefore, the correct answer is B as it aligns with the known pathogenicity of Coxsackie Viruses.

Correct Answer: B

Rationale: The correct answer is B: Polysaccharide capsule. The capsule of Neisseria meningitidis is crucial for its virulence as it helps the bacteria evade the host immune system by inhibiting phagocytosis. This allows the bacteria to survive and multiply in the host, leading to invasive infections. Exotoxins, beta-lactamase, and pyrogenic toxins are not the main virulence factors of Neisseria meningitidis and do not play as significant a role in its pathogenicity as the polysaccharide capsule.

Correct Answer: B

Rationale: The correct answer is B: Enable bacterial adherence to surfaces. Bacterial capsules are a protective layer outside the cell wall that helps bacteria adhere to surfaces and evade host immune responses. This allows bacteria to colonize and infect host tissues. A: Enhancing bacterial motility is typically associated with flagella, not capsules. C: Bacterial DNA replication is not directly affected by capsules. D: Bacterial capsules do play a role in protecting bacteria from desiccation by providing a barrier against drying out. However, the primary function is enabling adherence to surfaces.

Correct Answer: D

Rationale: The correct answer is D, "All of the above." Clostridium botulinum causes botulism, Salmonella enterica causes salmonellosis, and Escherichia coli can cause foodborne illnesses such as E. coli infection. All three bacteria are associated with foodborne illnesses due to contamination of food or water sources. Therefore, selecting "All of the above" is the most appropriate choice as it includes all the bacteria commonly linked to foodborne illnesses. The other choices (A, B, and C) are incorrect because they do not encompass all the bacteria associated with foodborne illnesses as stated above.

Correct Answer: A

Rationale: The correct answer is A: Cell wall. Mycoplasma species lack a cell wall, making them unique among bacteria. This is because they have a flexible cell membrane that provides structural support instead of a rigid cell wall. The absence of a cell wall allows them to be pleomorphic and gives them resistance to certain antibiotics targeting cell wall synthesis. Plasma membrane (B), DNA (C), and ribosomes (D) are present in Mycoplasma species, so they are not the correct answer.

Correct Answer: C

Rationale: The correct answer is C: Salmonella. This bacterium should be handled in a Biosafety Level 2 facility due to its potential to cause disease in humans. Salmonella is a pathogenic bacterium that can cause foodborne illnesses and infections. Handling it in a Biosafety Level 2 facility ensures proper containment and protection of personnel. A: Micrococcus luteus and B: Bacillus subtilis are common environmental bacteria that do not pose significant risks to human health, so they can be safely handled in lower biosafety levels. D: Staphylococcus epidermidis is a common skin commensal bacterium that is generally not considered highly pathogenic, so it does not require Biosafety Level 2 containment.

Correct Answer: A

Rationale: The correct answer is A: Hyperresponsiveness reaction type IV. This type of reaction, also known as delayed-type hypersensitivity, is characterized by the activation of T lymphocytes and macrophages, leading to inflammation at the site of antigen exposure. In the case of the Mantoux test, the appearance of a papule 48 hours later indicates a delayed hypersensitivity reaction mediated by T cells. Choice B: Reaction of Arthus phenomenon type is incorrect as this type of reaction involves immune complexes forming in the blood vessels leading to tissue damage, which is not the mechanism seen in the Mantoux test reaction. Choice C: Reaction of serum sickness type is incorrect as this type of reaction involves the formation of immune complexes in the blood leading to systemic symptoms like fever, rash, and joint pain, which is not typically seen in the Mantoux test reaction. Choice D: Atopic reaction is incorrect as atopic reactions involve IgE antibodies and mast cell degranulation, which are not the mechanisms