Which is the preferred mode of transmission of HIV from a mother to a child?

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: D

Rationale: The correct answer is D: commensalism. In commensalism, one organism benefits while the other is neither helped nor harmed. In this relationship, the waste product of one organism serves as a nutrient source for another without affecting the first organism. Mutualism (A) involves both organisms benefiting, competition (B) involves a struggle for resources, and synergism (C) involves cooperative interactions. Commensalism is the only choice where one organism benefits from the waste product of another without any impact on the producer.

Correct Answer: B

Rationale: The correct answer is B: Cholera. Cholera is caused by Gram-negative curved rod-like bacteria called Vibrio cholerae, commonly found in contaminated water or food. The characteristic symptom of cholera is profuse watery diarrhea, which matches the patient's presentation. Typhoid fever (A) is caused by Salmonella typhi, which is not a curved rod-like bacteria. Diphtheria (C) is caused by Corynebacterium diphtheriae, a Gram-positive bacterium, and does not typically cause diarrhea. Intestinal form of plague (D) is caused by Yersinia pestis, which is not a curved rod-like bacteria and does not typically present with diarrhea.

Correct Answer: C

Rationale: The correct answer is C: Thick peptidoglycan layer. Gram-positive bacteria have a thick peptidoglycan layer in their cell wall, which retains the crystal violet stain in the Gram staining process, leading to a purple color. This thick layer is a defining characteristic of Gram-positive bacteria. Rationale: A: Thin peptidoglycan layer is incorrect because Gram-positive bacteria have a thick peptidoglycan layer. B: Presence of an outer membrane is incorrect because Gram-positive bacteria lack an outer membrane. D: Presence of lipopolysaccharides is incorrect because lipopolysaccharides are typically found in the outer membrane of Gram-negative bacteria, not Gram-positive bacteria.

Correct Answer: D

Rationale: The correct answer is D: stereomicroscopes. These types of microscopes, also known as dissecting microscopes, are designed for observing larger objects like insects or worms. They have a lower magnification power compared to electron microscopes (A), which are used to observe smaller objects at a much higher resolution. Dark-field microscopes (B) are used for observing live and unstained samples with high contrast, not specifically for larger objects. Fluorescence microscopes (C) are used to observe specimens that fluoresce under specific wavelengths of light, not necessarily for large objects like insects or worms. Therefore, the most suitable choice for observing fairly large objects like insects or worms is stereomicroscopes.

Correct Answer: A

Rationale: The correct answer is A: Clostridium tetani. Clostridium tetani is responsible for causing tetanus by producing a neurotoxin called tetanospasmin. This neurotoxin blocks inhibitory signals in the central nervous system, leading to muscle spasms and stiffness characteristic of tetanus. Clostridium perfringens (B) causes gas gangrene, Streptococcus pyogenes (C) causes strep throat, and Escherichia coli (D) can cause gastrointestinal infections but not tetanus. Therefore, based on the specific pathogen and its mechanism of action, Clostridium tetani is the correct answer.

Correct Answer: A

Rationale: The correct answer is A: Pseudomonas aeruginosa. Pseudomonas aeruginosa is known to produce green colonies on Endo agar due to its pyoverdin pigment. It is also a Gram-negative rod. P. aeruginosa commonly causes respiratory infections in immunocompromised patients. Escherichia coli (B) typically produces pink colonies on Endo agar and is more associated with gastrointestinal infections. Salmonella typhi (C) and Shigella dysenteriae (D) are both Enterobacteriaceae that usually do not produce green colonies on Endo agar and are more associated with gastrointestinal infections as well.

Correct Answer: D

Rationale: The correct answer is D because Borrelia burgdorferi cannot be detected with Giemsa stain. Giemsa stain is commonly used to visualize blood smears for malaria parasites but is not effective for Borrelia burgdorferi detection. A: Borrelia burgdorferi can be cultivated on blood agar - This is correct. Borrelia burgdorferi can be grown in culture on a special medium like Barbour-Stoenner-Kelly (BSK) agar. B: Borrelia burgdorferi is flexible, motile spirochete - This is correct. Borrelia burgdorferi is a spiral-shaped bacterium that moves using a corkscrew motion. C: Borrelia burgdorferi is transmitted by arthropods- ticks - This is correct. Borrelia burgdorferi is primarily transmitted to humans through the bite of infected ticks, particularly Ixodes

Correct Answer: D

Rationale: Step 1: Streptococcus pneumoniae is a common cause of community-acquired pneumonia. Step 2: Mycobacterium tuberculosis can lead to tuberculosis, which can manifest as pulmonary tuberculosis. Step 3: Escherichia coli is not typically associated with causing pneumonia. Step 4: Since Streptococcus pneumoniae and Mycobacterium tuberculosis are linked to pneumonia, and Escherichia coli is not, the correct answer is D - All of the above.