Gram-positive cocci arranged in chains were found in a wound smear. The bacteria were catalase-negative and beta-hemolytic on blood agar. What is the causative agent?

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pyogenes. This bacterium fits all the given characteristics: Gram-positive cocci arranged in chains, catalase-negative, and beta-hemolytic on blood agar. Streptococcus pyogenes is known for causing skin and soft tissue infections. Staphylococcus aureus (B) is catalase-positive and typically forms clusters, not chains. Enterococcus faecalis (C) is catalase-negative but not beta-hemolytic. Micrococcus luteus (D) is catalase-positive and not typically associated with wound infections.

Correct Answer: A

Rationale: The correct answer is A because immunofluorescence slides are examined under a fluorescence microscope with a x100 oil immersion objective. This is because immunofluorescence relies on the detection of fluorescently labeled antibodies, which emit light when excited by a specific wavelength. Using a fluorescence microscope allows for visualization of these labeled antibodies at high magnification and resolution, enabling precise examination of cellular structures and protein localization. Choice B is incorrect as light microscopes are not suitable for visualizing fluorescence. Choice C is incorrect as electron microscopes use electrons, not light, for imaging, which is not compatible with immunofluorescence. Choice D is incorrect as there is a specific method for examining immunofluorescence slides.

Correct Answer: B

Rationale: The correct answer is B: mitochondria. Stroma is a component of chloroplasts, not mitochondria. Lysosomes contain hydrolytic enzymes, not stroma. Mitochondria have an inner and outer membrane structure, with the matrix containing the stroma where important metabolic processes occur. This is where the Krebs cycle and oxidative phosphorylation take place. Stroma in chloroplasts is where photosynthesis occurs. So, the correct answer is B because stroma is a component of mitochondria, where crucial energy production processes happen.

Correct Answer: A

Rationale: The correct diagnosis is A: Balantidiasis. The presence of large ciliated protozoa with a kidney-shaped macronucleus is characteristic of Balantidium coli, the causative agent of balantidiasis. The ciliated trophozoites of Balantidium coli are unique compared to the other choices. Giardiasis is caused by Giardia lamblia, which has flagella and not cilia. Amoebiasis is caused by Entamoeba histolytica, which lacks cilia. Trichomoniasis is caused by Trichomonas vaginalis, which also lacks cilia. Therefore, based on the specific morphology described, the correct diagnosis is Balantidiasis.

Correct Answer: C

Rationale: Rationale: C is the correct answer because antibodies formed against Mycobacterium tuberculosis are not protective. They do not efficiently clear the infection due to the bacterium's ability to evade the immune response by residing intracellularly in macrophages. Antibodies play a minimal role in controlling tuberculosis compared to cell-mediated immunity. Summary: A is incorrect because Mycobacterium tuberculosis does contain mycolic acid in its cell wall. B is incorrect because the pathogen can indeed live intracellularly in macrophages. D is incorrect as C is the correct answer.

Correct Answer: B

Rationale: The correct answer is B: Contains single-stranded RNA with negative polarity. Measles virus is an enveloped virus with a single-stranded RNA genome that is negative-sense. This means it must first be transcribed into positive-sense RNA before it can be translated. Choice A is incorrect as the measles virus does have an outer envelope. Choice C is incorrect as measles virus belongs to the family Paramyxoviridae, not Togaviridae. Choice D is incorrect as measles virus can be grown on cell cultures, specifically on Vero cells.

Correct Answer: A

Rationale: Step 1: Rubella virus belongs to the Togaviridae family, which typically exhibits icosahedral symmetry. Step 2: Icosahedral symmetry refers to a structure with 20 equilateral triangular faces, which is characteristic of many viruses, including rubella. Step 3: Therefore, choice A is correct as rubella virus indeed has icosahedral type of symmetry. Summary: - Choice B is incorrect as rubella virus is an ssRNA virus, not ssDNA. - Choice C is incorrect as rubella virus does have an envelope derived from the host cell membrane. - Choice D is incorrect as rubella virus does have glycoprotein spikes on its surface.

Correct Answer: A

Rationale: The correct answer is A: Neutralization. In this scenario, the antibotulinic serum of types A, B, and E were introduced to neutralize the botulinum toxin in the test specimen. The serological reaction applied here involves the neutralization of the toxin by the specific antibodies present in the serum. This process prevents the toxin from causing harm to the mice. Summary of other choices: B: Precipitation - This involves the formation of insoluble complexes between antigen and antibody, not the specific neutralization seen in this case. C: Complement binding - This involves activation of the complement system leading to cell lysis, not the direct neutralization of toxin. D: Double immune diffusion - This technique is used to determine the presence of specific antibodies or antigens based on their diffusion patterns, not the neutralization of toxin as seen in this scenario.

Correct Answer: B

Rationale: The correct answer is B: Pseudomonas aeruginosa. This bacterium is important for controlling air quality as it can degrade a wide range of organic compounds present in the air, helping to maintain a clean and healthy environment. Alpha and beta-hemolytic streptococci (Choice A) are not typically associated with air quality control. E. coli (Choice C) and Salmonella spp. (Choice D) are more commonly found in water and food sources, not air, making them incorrect choices for this question. Pseudomonas aeruginosa's ability to break down organic matter in the air makes it the most suitable option for maintaining sanitary air quality.