A wound culture from a patient with an infected ulcer revealed Gram-positive rods with terminal spores. What is the most likely causative agent?

Correct Answer: A

Rationale: Step-by-step rationale: 1. Gram-positive rods with terminal spores suggest Clostridium genus. 2. Terminal spores are characteristic of Clostridium perfringens. 3. C. perfringens is known to cause wound infections. 4. Therefore, the most likely causative agent is Clostridium perfringens. Summary: A: Clostridium perfringens is correct due to its characteristic features and association with wound infections. B: Bacillus anthracis does not typically form terminal spores. C: Clostridium tetani causes tetanus, not wound infections. D: Bacillus cereus does not produce terminal spores like Clostridium perfringens.

Correct Answer: B

Rationale: The correct answer is B: Agglutination. During a suspected plague outbreak, agglutination testing is used to quickly identify the antigen of the causative agent. In this test, specific antibodies are added to a sample containing the suspected antigen. If the antigen is present, it will clump together (agglutinate) with the antibodies, indicating a positive result. This method is rapid and efficient for identifying the presence of the plague-causing agent. Choice A: Precipitation involves the formation of a visible precipitate when antigen and antibody react, but it is not as quick or specific as agglutination for identifying the antigen in this scenario. Choice C: Passive hemagglutination is a variation of agglutination that uses red blood cells as carriers for antigens or antibodies. While it can be useful in certain situations, it is not typically the first choice for rapid identification of plague antigen. Choice D: Complement binding is a different type of

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: 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: A

Rationale: The correct answer is A: Capnophilic. Brucella requires a CO2 enriched atmosphere for cultivation, making it capnophilic. This is because Brucella is a microaerophilic bacterium that thrives in low oxygen conditions and elevated CO2 levels. Choice B (Facultative anaerobic) and D (Obligate aerobic) are incorrect as Brucella does not grow well under aerobic conditions. Choice C (Obligate anaerobic) is also incorrect as Brucella can grow in the presence of oxygen, although it prefers low oxygen environments.

Correct Answer: B

Rationale: The correct answer is B: Mycobacterium leprae. This microorganism can only be cultured in the footpads of mice or a species of armadillo due to its specific growth requirements. Mycobacterium tuberculosis (choice A) can be cultured in various culture media in the laboratory. Neisseria gonorrhoeae (choice C) can be cultured on selective media like Thayer-Martin agar. Mycoplasma (choice D) can be cultured in cell cultures or specialized media. Therefore, the unique growth pattern of Mycobacterium leprae makes it the correct answer.

Correct Answer: D

Rationale: The correct answer is D: five. Escherichia coli can cause enterotoxigenic E. coli (ETEC), enteroinvasive E. coli (EIEC), enterohemorrhagic E. coli (EHEC), enteroaggregative E. coli (EAEC), and diffusely adherent E. coli (DAEC). Each form has distinct characteristics and pathogenesis. Therefore, the other choices (A, B, C) are incorrect because they do not accurately represent the number of known forms of gastroenteritis caused by Escherichia coli.

Correct Answer: D

Rationale: The correct answer is D because viruses are sensitive to interferon, a natural defense mechanism of the body against viral infections. Interferon helps to inhibit viral replication. A: Viruses are cell-free infectious particles, not living systems. B: Viruses are obligate intracellular parasites as they require host cells to replicate. C: Viruses can have either DNA or RNA as genetic material, which is a characteristic feature.

Correct Answer: B

Rationale: The correct answer is B: Transformation. Frederick Griffith discovered bacterial transformation, where genetic material can be transferred between bacteria. He observed this phenomenon while studying pneumonia-causing bacteria in 1928. Transformation is the process by which bacteria take up external DNA and incorporate it into their own genome. This discovery was crucial in understanding how genetic information can be transferred between organisms. Rationale for other choices: A: Translation - This term refers to the process of protein synthesis from mRNA, not relevant to Griffith's discovery. C: Transcription - This term refers to the process of synthesizing RNA from DNA, not related to Griffith's discovery. D: Conjugation - This term refers to the direct transfer of genetic material between bacterial cells through cell-to-cell contact, which is different from the phenomenon Griffith observed.