A patient with a productive cough and fever had a Gram-positive cocci isolated from a sputum sample. The bacteria were catalase-positive and coagulase-negative. What is the likely microorganism?

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus epidermidis. 1. Gram-positive cocci suggest a staphylococcal species. 2. Catalase-positive indicates it belongs to the Staphylococcus genus. 3. Coagulase-negative rules out Staphylococcus aureus. 4. Staphylococcus epidermidis is a common cause of infections in immunocompromised patients. Summary: - B: Staphylococcus aureus is coagulase-positive. - C: Streptococcus pneumoniae is a Gram-positive diplococci. - D: Neisseria meningitidis is a Gram-negative diplococci.

Correct Answer: C

Rationale: The correct answer is C (Both A and B) because both Clostridium botulinum and Bacillus anthracis are capable of producing spores. Spores are highly resistant structures that allow bacteria to survive harsh environmental conditions. Clostridium botulinum and Bacillus anthracis produce spores as a survival mechanism when conditions become unfavorable. Choice A (Clostridium botulinum) is incorrect because it only represents one of the bacteria capable of producing spores. Choice B (Bacillus anthracis) is also incorrect as it alone does not encompass all bacteria capable of producing spores. Choice D (None of the above) is incorrect as both bacteria mentioned can produce spores.

Correct Answer: C

Rationale: The correct answer is C: Quinine. Quinine is known for its destructive effect on erythrocytic forms of malarial plasmodia and dysenteric amoebae. It is commonly used for the treatment and prevention of diseases such as malaria, amebiasis, and interstitial disease. Quinine works by interfering with the parasite's ability to break down hemoglobin in red blood cells, ultimately leading to their destruction. Incorrect choices: A: Chingamin - Chingamin is not typically used to treat malaria, amebiasis, or interstitial disease. B: Emetine hydrochloride - Emetine hydrochloride is primarily used for treating amoebic dysentery and is not commonly used for malaria treatment. D: Erythromycin - Erythromycin is an antibiotic used to treat bacterial infections, not parasitic infections like malaria or amebiasis.

Correct Answer: A

Rationale: The correct answer is A: Acid resistance. The Ziehl-Neelsen staining technique is specifically used to detect acid-fast bacteria like Mycobacterium tuberculosis, which is resistant to acid decolorization. This property allows the tuberculosis bacillus to retain the stain even after exposure to acid-alcohol, appearing red under the microscope. Explanation of incorrect choices: B: Alkali resistance - This property is not relevant in the context of Ziehl-Neelsen staining for acid-fast bacteria. C: Alcohol resistance - While alcohol resistance is related to acid-fastness, it is not the specific property highlighted by Ziehl-Neelsen staining. D: Capsule formation - Capsule formation is a different characteristic and not directly related to the staining behavior of acid-fast bacteria in the Ziehl-Neelsen technique.

Correct Answer: A

Rationale: The correct answer is A: Actinomycosis. This is supported by the presence of purulent foci with druses consisting of short rod-like elements attached to a homogenous center, which is characteristic of Actinomyces species. Actinomycosis commonly presents with granulation tissue and connective tissue formation. B: Tuberculosis does not typically present with druses containing short rod-like elements. C: Syphilis does not typically present with purulent foci or druses. D: Candidosis does not typically present with the described features of purulent fluxing and druses with short rod-like elements.

Correct Answer: D

Rationale: The correct answer is D: lyases. Lyases are enzymes that catalyze the breaking of chemical bonds without the addition of water. They can remove functional groups from substrates or add functional groups to double bonds without the use of water. A: Oxidoreductases involve the transfer of electrons. B: Transferases transfer functional groups from one molecule to another. C: Hydrolases catalyze the breaking of bonds by adding water.

Correct Answer: A

Rationale: The correct answer is A: Escherichia coli. E. coli is a Gram-negative rod that ferments lactose, leading to red colonies on Endo agar. This bacterium is commonly found in the human gut and is known for its ability to ferment lactose. Salmonella and Shigella are also Gram-negative rods but do not ferment lactose, so they would not produce red colonies on Endo agar. Proteus is a Gram-negative rod that is not known for its lactose-fermenting ability and would not produce red colonies on Endo agar. Therefore, based on the characteristics provided, E. coli is the most likely microorganism responsible for the red colonies on Endo agar.

Correct Answer: A

Rationale: The Ascoli precipitation test is specifically used to detect anthrax agent antigens. The test involves mixing a patient's serum with a solution containing anthrax antigens, leading to precipitation if the antigens are present. Therefore, a positive reaction in this test indicates the presence of anthrax agent antigens. The other choices (B: Brucellosis agent, C: Anaerobic infection toxin, D: Plague agent) are incorrect because the Ascoli precipitation test is not designed to detect these specific agents or toxins.

Correct Answer: B

Rationale: Facultative anaerobes can switch between aerobic and anaerobic metabolism based on oxygen availability. This flexibility enables them to grow in both oxygen-rich and oxygen-poor environments, making choice B correct. Choice A is incorrect because facultative anaerobes do not require oxygen for survival. Choice C is incorrect as obligate anaerobes cannot grow in the presence of oxygen. Choice D is incorrect because obligate anaerobes cannot tolerate any amount of oxygen.