A blood culture from a patient with sepsis revealed Gram-negative diplococci. The organism was oxidase-positive and fermentative. What is the most likely causative agent?

Correct Answer: B

Rationale: The correct answer is B: Neisseria meningitidis. This is because Neisseria meningitidis is a Gram-negative diplococci that is oxidase-positive and fermentative. Neisseria gonorrhoeae (choice A) is also a Gram-negative diplococci but is not fermentative. Haemophilus influenzae (choice C) is not a diplococci and Moraxella catarrhalis (choice D) is oxidase-negative. Thus, Neisseria meningitidis fits all the criteria provided in the question, making it the most likely causative agent for the sepsis in this patient.

Correct Answer: C

Rationale: The correct answer is C: prions. Prions are misfolded proteins that can cause transmissible spongiform encephalopathies like Creutzfeldt-Jakob disease. Prions are not viruses like flavoviruses (A) or orthomyxoviruses (D). Virusoids (B) are small, circular, single-stranded RNA molecules that require a helper virus to replicate and are not associated with transmissible spongiform encephalopathies. Therefore, the correct answer is C as prions are the only choice that correctly links to the etiology of transmissible spongiform encephalopathies.

Correct Answer: D

Rationale: The correct answer is D because bacteremia can be caused by a variety of bacteria including S.epidermidis, E.coli, S.aureus, P.aeruginosa, K.pneumoniae, and resident skin diphtheroids. Bacteremia refers to the presence of bacteria in the bloodstream, which can occur due to infections from various sources. Choices A and B include common bacteria known to cause bacteremia, while choice C refers to resident skin diphtheroids that can also enter the bloodstream under certain conditions. Therefore, the correct answer is D as it encompasses all the possible etiological causes of bacteremia.

Correct Answer: A

Rationale: The correct answer is A: Metronidazole. Rationale: 1. Metronidazole is the drug of choice for amebic dysentery due to its effectiveness against the causative agent, Entamoeba histolytica. 2. Metronidazole has good tissue penetration and is able to reach the site of infection in the gut. 3. It is a bactericidal drug that acts by disrupting the DNA structure of the parasite. 4. Metronidazole is well-absorbed orally and has minimal side effects. Summary of other choices: B: Furazolidonum - Not the drug of choice for amebic dysentery. It is primarily used for treating bacterial diarrhea. C: Levomycetin - Not effective against Entamoeba histolytica and not recommended for amebic dysentery. D: Phthalazol - Not commonly used for amebic dysentery treatment. Metronidazole is preferred due

Correct Answer: D

Rationale: The correct answer is D: All are correct. Culture of samples from the respiratory tract can identify specific pathogens, Immunofluorescence can detect viral antigens, and PCR can amplify and detect specific DNA/RNA sequences. Using all methods together provides a comprehensive approach for diagnosing respiratory tract infections. Culture alone may miss fastidious organisms, Immunofluorescence has limitations in sensitivity, and PCR requires specific primers. Therefore, combining these methods increases the likelihood of accurate diagnosis by covering a range of pathogens and improving sensitivity and specificity.

Correct Answer: A

Rationale: The correct answer is A: Clostridium tetani. This bacterium is known for causing tetanus due to its ability to produce tetanospasmin, a neurotoxin that leads to the characteristic muscle stiffness and spasms seen in tetanus. Clostridium perfringens (Choice B) is associated with gas gangrene, Streptococcus pyogenes (Choice C) causes streptococcal infections, and Escherichia coli (Choice D) is known for causing various gastrointestinal infections. Therefore, Choices B, C, and D are incorrect as they are not the causative agents of tetanus.

Correct Answer: A

Rationale: The correct answer is A: Mycolic acid. Ziehl-Neelsen method is used to stain acid-fast bacteria, such as Mycobacterium species. Mycolic acid in the cell wall of these bacteria resists decolorization, leading to red-colored bacilli on a blue background. Capsule, flagella, and endospores do not play a role in this staining property. Capsules are usually stained using special techniques, flagella are not typically visible with this stain, and endospores are stained using the Schaeffer-Fulton method.

Correct Answer: D

Rationale: Step-by-step rationale for why answer choice D is correct: 1. Coronaviruses can cause reinfections due to potential waning immunity. 2. Studies have shown cases of reinfections with different strains or within a short period. 3. This contradicts the notion that reinfections cannot be observed. Summary: A: Incorrect because some coronaviruses can cause lower respiratory tract infections. B: Incorrect as coronaviruses can exhibit varied symptomatology including asymptomatic cases. C: Incorrect as some coronaviruses like SARS can lead to severe pneumonia and complications.

Correct Answer: A

Rationale: The correct answer is A: Tetanus. The symptoms of tonic tension of the masticatory muscles following a dog bite are indicative of tetanus, caused by the bacterium Clostridium tetani. The incubation period of tetanus is usually 3-21 days, consistent with the patient's history of being bitten 12 days ago. Tetanus toxin causes muscle stiffness and spasms, leading to the inability to open the mouth. Rabies (B) presents with hydrophobia and neurological symptoms. Hysteria (C) is a psychological condition. Trigeminal neuralgia (D) is characterized by severe facial pain, not muscle stiffness.