Which of the following is a type of acute infection generally caused by group A Streptococcus?

Correct Answer: C

Rationale: The correct answer is C: Erysipelas. Erysipelas is a type of acute infection caused by group A Streptococcus bacteria. This bacteria infects the upper dermis and superficial lymphatics, leading to a distinct raised, well-demarcated, erythematous skin lesion. The other choices are incorrect because: A Carbuncle is a deep skin infection involving hair follicles, B Impetigo is a superficial skin infection caused by Staphylococcus or Streptococcus bacteria, and D Acne is a chronic inflammatory skin condition not typically caused by group A Streptococcus.

Correct Answer: A

Rationale: The correct answer is A: 4 and 250. Coli index is calculated by dividing the number of red colonies by the volume of water analyzed, which gives 2 red colonies / 500 ml = 4. Coli titer is the reciprocal of the coli index, so it is 1 / 4 = 250. This indicates the concentration of coliform bacteria in the water sample. Choices B, C, and D are incorrect as they do not follow the correct calculation steps for determining the coli index and coli titer. B has the correct coli index but incorrect coli titer. C and D have the values reversed, leading to incorrect results.

Correct Answer: D

Rationale: The correct answer is D: All of the above. Streptococcus pneumoniae, Mycobacterium tuberculosis, and Escherichia coli can all cause pneumonia, but through different mechanisms. S. pneumoniae is a common cause of community-acquired pneumonia, M. tuberculosis can lead to tuberculosis-related pneumonia, and E. coli can cause pneumonia in immunocompromised individuals. Therefore, all three bacteria can be responsible for causing pneumonia, making option D the correct choice. Option A, Streptococcus pneumoniae, is correct but does not cover all possible causes of pneumonia. Option B, Mycobacterium tuberculosis, is too specific and does not include other common causes. Option C, Escherichia coli, is also a possible cause of pneumonia but does not account for all potential pathogens.

Correct Answer: D

Rationale: The correct answer is D: Loefler. This staining method is used for identifying Corynebacterium diphtheriae, the causative agent of diphtheria. It involves using methylene blue and basic fuchsin to stain the bacteria. The yellow bacilli with blue grains at their ends indicate the characteristic appearance of C. diphtheriae when stained using the Loefler method. Choice A: Ziehl-Nielsen is used for acid-fast bacteria like Mycobacterium tuberculosis. Choice B: Kozlovsky is not a standard staining method in microbiology. Choice C: Romanovsky is used for blood smears to identify malaria parasites.

Correct Answer: C

Rationale: The correct answer is C: phialospores. Phialospores are conidiospores that bud off from a vase-shaped spore-bearing cell called a phialide. This structure is characteristic of fungi in the genus Penicillium. Arthrospores (A) are formed by the fragmentation of hyphae, porospores (B) are not a recognized term in mycology, and blastospores (D) are produced by budding from yeast cells. Therefore, C is the correct choice based on the specific description provided in the question.

Correct Answer: B

Rationale: The correct answer is B: Clostridium tetani. This bacterium produces tetanospasmin toxin, causing tetanus. Clostridium botulinum (choice A) produces botulinum toxin, leading to botulism. Bacillus anthracis (choice C) causes anthrax, not tetanus. Staphylococcus aureus (choice D) can cause various infections, but not tetanus. Therefore, only Clostridium tetani is the causative agent of tetanus.

Correct Answer: A

Rationale: The correct answer is A: Treponema. Treponema pallidum is a spirochete bacterium that appears as long, thin, and spiral-shaped microorganisms with 8-12 regular coils under the microscope. This characteristic morphology is specific to Treponema species, making it the correct choice. Borrelia, Leptospira, and Vibrios have different shapes and arrangements under the microscope, making them incorrect choices in this scenario.

Correct Answer: A

Rationale: The correct answer is A: Neisseria species. Gram staining differentiates bacteria based on cell wall composition. Gram-negative bacteria like Neisseria have a thin peptidoglycan layer and an outer membrane, making them appear pink under the microscope. Streptococcus species (B) are Gram-positive cocci with a thick peptidoglycan layer, appearing purple. Bacillus (C) and Clostridium (D) species are Gram-positive rods, not Gram-negative cocci. Thus, the correct answer is A because Neisseria species are the only Gram-negative cocci among the choices provided.

Correct Answer: A

Rationale: The correct answer is A: Toxoplasma. The crescent-shaped protozoa with pointed ends and blue cytoplasm described in the question are characteristic of Toxoplasma gondii, the causative agent of toxoplasmosis. Toxoplasma staining with Romanovsky-Giemsa method typically shows these specific morphological features. Plasmodium causes malaria and does not exhibit the described morphology. Leishmania and Trypanosoma are both kinetoplastid parasites, but they do not typically present as crescent-shaped protozoa with blue cytoplasm. Therefore, based on the specific characteristics described in the question, the correct answer is Toxoplasma.