A male patient has been diagnosed with gastric ulcer. Bacteriological examination of biopsy material from the affected part of stomach revealed small colonies of gram-negative, oxide reductase-positive flexibacteria that grew on the chocolate agar on the fifth day. Which of the following microorganisms is the most likely causative agent?

Correct Answer: A

Rationale: The correct answer is A: Helicobacter pylori. This bacterium is the most likely causative agent of gastric ulcers. Here's the rationale: 1. Helicobacter pylori is commonly associated with gastric ulcers. 2. It is a gram-negative bacterium that grows on chocolate agar and is oxide reductase-positive. 3. The slow growth on the fifth day is characteristic of H. pylori. 4. Campylobacter jejuni and Campylobacter fetus are not typically associated with gastric ulcers. 5. Mycoplasma hominis is a bacterium that lacks a cell wall and is not commonly found in gastric ulcers.

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus aureus and hemolytic streptococcus. These microorganisms are commonly found in high concentrations during sanitary and bacteriological examination of air in a drugstore due to their prevalence in the environment. Staphylococcus aureus and hemolytic streptococcus are known to be significant pathogens that can cause various infections in humans. Rationale: 1. Staphylococcus aureus and hemolytic streptococcus are common pathogens found in the environment and can easily contaminate air in enclosed spaces like a drugstore. 2. Both microorganisms are considered to be of sanitary significance as they can cause infections and are indicators of poor hygiene and sanitation. 3. Diphtheritic and tuberculous bacilli (Choice B) are not typically associated with air contamination in a drugstore setting. 4. Colibacilli and blue pus bacilli (Choice C) are more commonly found in fecal

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: D

Rationale: The correct answer is D: Chocolate agar. Neisseria meningitidis is a fastidious organism that requires enriched media for growth. Chocolate agar contains heat-treated blood that provides essential nutrients for the growth of N. meningitidis. The other choices, A: Levine agar, B: Lowenstein-Jensen agar, and C: TCBS agar, do not provide the specific nutrients required for the growth of N. meningitidis. Therefore, only choice D, Chocolate agar, supports the growth of N. meningitidis due to its enriched composition.

Correct Answer: A

Rationale: The correct answer is A: Neisser staining method. Neisser staining method is used to stain diphtheria bacilli, which appear as blue rods with thickenings at the poles. The rationale is that Neisser staining specifically targets and highlights the characteristics of the diphtheria bacilli. Incorrect choices: B: Gram staining is not specific for diphtheria bacilli and does not show the characteristic blue rods with thickenings at the poles. C: Ziehl-Neelsen staining is used for acid-fast bacteria like Mycobacterium tuberculosis, not for diphtheria bacilli. D: Loeffler staining is used for diphtheria bacilli but does not produce blue rods with thickenings at the poles as seen in this case.