A patient with a severe case of pneumonia had sputum stained using the Gram method. The smear revealed Gram-positive cocci arranged 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 a common cause of pneumonia and is characterized by being Gram-positive cocci arranged in pairs with a capsule, as described in the question. The presence of a capsule is a key characteristic of Streptococcus pneumoniae, distinguishing it from the other choices. Staphylococcus aureus (B) is a Gram-positive cocci, but it typically forms clusters, not pairs. Klebsiella pneumoniae (C) is a Gram-negative rod, not a Gram-positive cocci. Enterococcus faecalis (D) is a Gram-positive cocci, but it does not typically present with a capsule in the same way Streptococcus pneumoniae does.

Correct Answer: C

Rationale: The correct answer is C: urethra. Resident microflora refers to the normal, beneficial bacteria that inhabit a specific area of the body without causing harm. The urethra is one of the locations where resident microflora are commonly found. These bacteria play a vital role in maintaining a healthy balance and preventing harmful pathogens from colonizing the urethra. Blood (A), lung (B), and cerebro-spinal fluid (D) are not typical locations for resident microflora as these areas are usually sterile or have very limited microbial presence to prevent infections.

Correct Answer: C

Rationale: The correct answer is C: Bacterial adhesion to the surface of the host cells, conjugation. Villi and cilia on the cell surface of pathogenic bacteria help in bacterial adhesion to host cells, facilitating the process of infection. Conjugation is the transfer of genetic material between bacterial cells, which can be aided by these structures. The other choices are incorrect because RNA exchange between cells (A) is typically facilitated by different structures like pili, inhibition of complement activity (B) is not related to the function of villi and cilia, and resistance to antibody opsonization (D) is usually achieved through other mechanisms such as capsule formation.

Correct Answer: A

Rationale: The correct answer is A: Rotavirus. Rotavirus is a member of the Reoviridae family known for causing diarrhea in infants. It infects the lining of the small intestine, leading to symptoms like vomiting and watery diarrhea. Rationale: 1. Rotavirus is specifically known for causing diarrhea in infants. 2. Reoviruses are a family of viruses to which rotavirus belongs. 3. Congovirus (B), Hepadnavirus (C), and Picornavirus (D) do not belong to the Reoviridae family and are not associated with causing diarrhea in infants. In summary, choice A is correct as it aligns with the characteristics of the given family of viruses and their associated symptoms, while choices B, C, and D are incorrect as they do not fit these criteria.

Correct Answer: C

Rationale: The correct answer is C: Identification. Bacteria are studied by identification to determine their specific characteristics and differentiate between different species. Taxonomy (A) is the science of classification, not specific to bacteria. Classification (B) is the process of grouping organisms based on shared characteristics, not specific to bacteria. Nomenclature (D) is the naming system for organisms, not the primary method for studying bacteria. Therefore, identification (C) is the correct choice for studying bacteria.

Correct Answer: D

Rationale: The correct answer is D because the defense role of the skin is not related to lysozyme activity. Lysozyme is an enzyme found in tears, saliva, and mucus, not specifically in the skin. The skin's defense role is primarily related to its physical barrier function, low pH creating an acidic environment that inhibits microbial growth, secretion of antimicrobial peptides, and the activity of skin macrophages that phagocytose pathogens. Choices A, B, and C are true statements as they correctly describe different aspects of the skin's defense mechanisms.

Correct Answer: A

Rationale: The correct answer is A: BCG vaccination. The Mantoux test is used to detect tuberculosis infection. A negative reaction means the child is not infected. BCG vaccination is recommended for individuals without prior TB infection to prevent severe forms of the disease. Antitoxin and rabies vaccinations are not related to TB and are not indicated in this scenario. Repeating the Mantoux test is unnecessary since a negative result indicates absence of TB infection.

Correct Answer: D

Rationale: The most probable diagnosis is D: Tularemia. Tularemia is a bacterial infection caused by Francisella tularensis. The symptoms described align with tularemia, such as pain in axillary area, fever, shaky gait, coated tongue, frequent pulse, painful lymphatic nodules, and erythematous skin over nodules. The key features pointing towards tularemia are the presence of lymphadenitis in the axillary area and the erythematous, glistering skin over the nodules, which are characteristic of ulceroglandular tularemia. Bubonic plague (A) presents with painful, swollen lymph nodes called buboes but typically lacks the erythematous skin findings. Acute purulent lymphadenitis (B) usually presents with pus-filled lymph nodes but does not typically cause shaky gait or coated tongue. Lymphogranulomatosis (C) is a term for Hodgkin's lymphoma, which does not

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is a common cause of pneumonia and is characterized by being Gram-positive cocci arranged in pairs with a capsule, as described in the question. The presence of a capsule is a key characteristic of Streptococcus pneumoniae, distinguishing it from the other choices. Staphylococcus aureus (B) is a Gram-positive cocci, but it typically forms clusters, not pairs. Klebsiella pneumoniae (C) is a Gram-negative rod, not a Gram-positive cocci. Enterococcus faecalis (D) is a Gram-positive cocci, but it does not typically present with a capsule in the same way Streptococcus pneumoniae does.