A patient with a sore throat had a throat culture revealing Gram-positive cocci in pairs with a capsule. What is the most likely causative agent?

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is the most likely causative agent because it is a Gram-positive cocci in pairs with a capsule, which matches the description provided. S. pneumoniae is a common cause of bacterial pharyngitis and can present with sore throat. Summary of other choices: B: Staphylococcus aureus is a Gram-positive cocci in clusters, not pairs, and is not typically associated with sore throat. C: Neisseria meningitidis is a Gram-negative diplococcus and more commonly causes meningitis or septicemia, not sore throat. D: Klebsiella pneumoniae is a Gram-negative rod bacterium, not a Gram-positive cocci, and is not a common cause of sore throat.

Correct Answer: A

Rationale: The correct answer is A: Escherichia coli. On Endo agar, lactose-fermenting bacteria produce red colonies due to acid production. Escherichersia coli is a lactose-fermenting, gram-negative bacillus commonly found in the intestines. Salmonella and Shigella are lactose-negative and do not produce red colonies on Endo agar. Proteus is also lactose-negative and doesn't typically grow on Endo agar. Therefore, based on the lactose fermentation and colony color, Escherichia coli is the most likely microorganism present in the fecal sample.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Mycobacterium tuberculosis is the causative agent of tuberculosis. 2. Mycobacterium tuberculosis is a slow-growing, acid-fast bacterium. 3. It primarily infects the lungs and can spread to other parts of the body. 4. Bacillus anthracis causes anthrax, Clostridium tetani causes tetanus, and Treponema pallidum causes syphilis. 5. Therefore, choice A, Mycobacterium tuberculosis, is the correct answer for the bacteria responsible for tuberculosis.

Correct Answer: A

Rationale: The correct answer is A: Neisser. Bacterial capsules can be stained using the Neisser staining method because it specifically targets the capsule, making it visible under a microscope. Neisser staining involves using a combination of acidic and basic dyes to highlight the capsule structure. This method helps differentiate the capsule from the bacterial cell, aiding in the identification and study of capsules. Choices B, C, and D are incorrect because Cleat and Müller staining methods are not commonly used for staining bacterial capsules, and "None of the above" is incorrect as Neisser staining is a valid method for capsule staining.

Correct Answer: A

Rationale: The correct answer is A: Francisella tularensis. This bacterium is classified as a class A bioterrorism agent due to its high virulence and potential for mass casualties. It can cause tularemia, a severe and potentially fatal disease. The other choices, Hepatitis B, E. coli, and Bacillus subtilis, are not considered class A bioterrorism agents. Hepatitis B is a virus causing liver inflammation, E. coli is a common bacterium found in the gut, and Bacillus subtilis is a beneficial bacterium used in various industries. Therefore, Francisella tularensis is the correct choice based on its high pathogenicity and bioterrorism potential.

Correct Answer: B

Rationale: The correct answer is B: Trichomonas vaginalis. Trichomonas vaginalis is a protozoan parasite that can survive and grow in low moisture conditions. It does not require a host cell and can thrive in moist environments, making it able to grow on substances with very low moisture content. Giardia lamblia (A), Balantidium coli (C), and Entamoeba histolytica (D) are all parasites that require a host to survive and reproduce, making them unable to grow on substances with very low moisture content. Trichomonas vaginalis is the only organism among the choices that fits the criteria of being able to grow on low moisture substances.

Correct Answer: A

Rationale: The correct answer is A: Balantidium coli. Balantidium coli is a large ciliated protozoa with a kidney-shaped macronucleus, commonly found in the feces of individuals with dysentery symptoms. Its morphology matches the description given in the question, making it the most likely causative agent. Summary of other choices: B: Entamoeba histolytica - This is not the correct answer because Entamoeba histolytica is a small amoeba with no cilia and a different nucleus shape. C: Giardia lamblia - This is not the correct answer as Giardia lamblia is a flagellated protozoa with a pear-shaped nucleus, different from the description provided. D: Trichomonas hominis - This is not the correct answer as Trichomonas hominis is a flagellated protozoa with multiple flagella and an undulating membrane, which does not match the characteristics of the

Correct Answer: D

Rationale: The correct answer is D: All of the above. HIV can be transmitted from mother to child during delivery through mixing of blood, during pregnancy through the placenta, and via breastmilk during lactation. Each mode of transmission carries a risk of HIV transmission to the child due to the presence of the virus in the mother's blood and bodily fluids. It is important to note that all three modes contribute to the risk of mother-to-child transmission of HIV, and preventive measures should be taken to reduce this risk. Option A, during delivery through mixing of blood, is correct as HIV can be transmitted through exposure to infected blood during childbirth. Option B, during pregnancy through placenta, is also correct as the virus can cross the placenta and infect the fetus. Option C, via breastmilk during lactation, is correct as HIV can be present in breastmilk and transmitted to the child through breastfeeding. Therefore, the preferred mode of transmission of HIV from a mother to a child

Correct Answer: C

Rationale: The correct answer is C: ECHO virus infection. ECHO virus is transmitted via the fecal-oral route, meaning the virus is passed from feces to the mouth. This transmission occurs through contaminated food, water, or surfaces. Relapsed fever and spotted fever are generally transmitted by arthropod vectors like ticks. Pertussis, also known as whooping cough, spreads through respiratory droplets. Therefore, the fecal-oral route is not applicable to these diseases.