A patient with a productive cough and fever had a sputum smear revealing Gram-positive cocci in clusters. What is the most likely causative agent?

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus aureus. Staphylococcus aureus is a Gram-positive cocci bacterium that forms clusters and commonly causes pneumonia with a productive cough and fever. It is frequently found in sputum smears in such cases. Streptococcus pneumoniae (B) is another common cause of pneumonia but typically appears in pairs or chains, not clusters. Neisseria meningitidis (C) is a Gram-negative diplococcus that causes meningitis, not pneumonia. Klebsiella pneumoniae (D) is a Gram-negative bacterium that can cause pneumonia but appears as Gram-negative rods, not Gram-positive cocci in clusters.

Correct Answer: D

Rationale: The correct answer is D because fires from flammable metals require specialized Class D fire extinguishers designed to extinguish these unique types of fires. Class A, B, and C fire extinguishers are not suitable for flammable metal fires as they are designed for different types of materials and fire classes. Class A extinguishers are for ordinary combustibles, Class B for flammable liquids, and Class C for electrical fires. Therefore, Class D fire extinguishers are specifically designed for flammable metal fires, making them the correct choice for this scenario.

Correct Answer: C

Rationale: The correct answer is C: Mumps. Group II diseases are vaccine-preventable diseases that are communicable and can cause outbreaks. Mumps fits this criteria as it is preventable through vaccination, easily transmitted through respiratory droplets, and can lead to outbreaks in communities. Anthrax (A) is a zoonotic disease, Lyme disease (B) is transmitted by ticks, and Smallpox (D) has been eradicated.

Correct Answer: B

Rationale: The correct answer is B: Campylobacter jejuni. This bacteria is commonly associated with foodborne illnesses due to its presence in undercooked poultry and unpasteurized milk. Campylobacteriosis is a leading cause of bacterial gastroenteritis. Streptococcus pneumoniae (A) causes pneumonia, not foodborne illnesses. Mycobacterium tuberculosis (C) causes tuberculosis, not foodborne illnesses. Haemophilus influenzae (D) can cause respiratory infections but is not commonly associated with foodborne illnesses.

Correct Answer: C

Rationale: Step-by-step rationale for Choice C (Streptococcus pyogenes) being the correct answer: 1. Erysipelas is a skin infection characterized by well-defined red, inflamed skin areas. 2. Streptococcus pyogenes is a common causative agent of erysipelas. 3. This bacterium produces enzymes that break down skin proteins, leading to the characteristic symptoms of erysipelas. 4. Streptococcus pyogenes is known for causing skin infections, including erysipelas. Summary of why the other choices are incorrect: A. Pseudomonas aeruginosa: Typically causes opportunistic infections, but not commonly associated with erysipelas. B. Staphylococcus aureus: Can cause skin infections, but not typically associated with erysipelas. D. Candida albicans: Fungal infection, not a bacterium, and not known to cause erysipelas.

Correct Answer: A

Rationale: The correct answer is A: Syphilis. The presentation of painless inguinal lymph nodes, along with a small-sized ulcer with thickened edges and a "laquer" bottom of greyish color on the genital mucous membrane, is classic for primary syphilis. The painless nature of the lymph nodes and the specific characteristics of the ulcer are key features of syphilitic infection. Primary syphilis is caused by the bacterium Treponema pallidum and typically presents with a single, painless ulcer known as a chancre. It is important to consider syphilis in the differential diagnosis of genital ulcers. Summary of other choices: B: Tuberculosis - Unlikely, as tuberculosis typically presents with pulmonary symptoms and does not cause genital ulcers. C: Lepra - Unlikely, as leprosy does not typically present with painless inguinal lymph nodes and the specific ulcer characteristics described. D: Trophic ulcer - Unlikely

Correct Answer: B

Rationale: The correct answer is B: Chlamydia trachomatis. Elementary bodies (EBs) and reticular bodies (RBs) are two distinct forms of Chlamydia trachomatis, a bacterium causing various infections. EBs are the infectious form, while RBs are the replicative form within host cells. Mycoplasma genitalium (choice A) lacks a cell wall and does not have these specific morphological forms. Rickettsia prowazekii (choice C) is an obligate intracellular bacterium but does not exhibit the elementary and reticular body forms characteristic of Chlamydia trachomatis. Therefore, the correct answer is B, as only Chlamydia trachomatis exhibits the elementary and reticular bodies.

Correct Answer: A

Rationale: Rationale: 1. Corynebacterium diphtheriae is the correct answer as it is the bacteria responsible for causing diphtheria, characterized by a thick pseudomembrane in the throat. 2. Streptococcus pyogenes causes strep throat but does not produce a pseudomembrane. 3. Neisseria meningitidis causes meningitis and septicemia, not a throat pseudomembrane. 4. Bacillus cereus causes food poisoning, not throat-related symptoms.

Correct Answer: A

Rationale: The correct answer is A because adaptive immunity is not mainly observed in the skin and mucous membranes. Adaptive immunity is a systemic response that involves specific immune cells and antibodies targeting specific pathogens. It develops immune memory (B), meaning it can recognize and respond faster upon re-exposure to the same pathogen. Adaptive immunity also has specificity (C), as it can target specific antigens. Lastly, adaptive immunity is not evolutionarily newer in comparison to innate immunity (D), as both systems have co-evolved to provide comprehensive protection against pathogens.