During fibergastroscopy a patient with ulcer disease of the stomach, the mucosal biopsy is taken from the area of an ulcer. Impression smear is prepared from biopsy material and stained by Gram method; the rest of biopsy material is tested for urease activity. Microscopy of the impression smear revealed gram- negative spiral-shaped microorganisms, urease activity test is positive. What bacteria were detected?

Correct Answer: A

Rationale: The correct answer is A: Helicobacter pylori. Rationale: 1. Gram-negative spiral-shaped microorganisms match the morphology of Helicobacter pylori. 2. Positive urease activity is a characteristic feature of Helicjsonacter pylori. 3. Helicobacter pylori is specifically associated with gastric ulcers and is a common pathogen in the gastrointestinal tract. Summary: Choice B, Campilobacter jejuni, is a gram-negative curved bacterium but is not typically associated with gastric ulcers or urease activity. Choice C, Treponema pallidum, is a spirochete bacterium causing syphilis, which is not related to gastric ulcers. Choice D, Spirilla minor, is a generic term for spiral-shaped bacteria and is not a specific pathogen associated with gastric ulcers or urease activity.

Correct Answer: A

Rationale: Rationale: 1. Gram-positive cocci in pairs indicate Streptococcus pneumoniae. 2. Presence of a capsule points to S. pneumoniae as it has a polysaccharide capsule. 3. S. pneumoniae commonly causes sore throat. 4. Neisseria meningitidis, Haemophilus influenzae, and Klebsiella pneumoniae are not typically associated with sore throat.

Correct Answer: A

Rationale: The correct answer is A: Trichomonas vaginalis. Trichomonas vaginalis is a flagellated protozoa that causes the sexually transmitted infection trichomoniasis. The presence of an undulating membrane in vaginal discharge samples is characteristic of Trichomonas vaginalis. Giardia lamblia causes gastrointestinal illness, not vaginal infections. Trypanosoma brucei causes African sleeping sickness transmitted by tsetse flies. Leishmania donovani causes visceral leishmaniasis transmitted by sandflies.

Correct Answer: A

Rationale: The correct answer is A: Candida fungi. In the context of a 70-year-old man with angular cheilitis (lesion at the corners of the mouth) and stomatitis, the presence of large ovoid gram-positive cells points towards Candida species, which are yeast fungi. Candida is a common opportunistic pathogen that can cause oral thrush and angular cheilitis in immunocompromised individuals, such as elderly people. Candida fungi are known to appear as large ovoid cells under microscopic examination. Summary of other choices: B: Streptococci are gram-positive bacteria and are not typically associated with large ovoid cells seen in this case. C: Staphylococci are also gram-positive bacteria and are not known to present as large ovoid cells in this context. D: Neisseria are gram-negative bacteria and are not the usual etiological agents for oral lesions like angular cheilitis.

Correct Answer: A

Rationale: The correct answer is A because spheroplasts are bacteria with defective cell walls that have a parietal layer (peptidoglycan layer) and a defective peptidoglycan layer. This is because spheroplasts have lost their rigid cell wall structure, leading to an incomplete peptidoglycan layer. Choice B is incorrect as the cytoplasmic membrane is not directly affected by the loss of cell wall integrity. Choice C is incorrect because spheroplasts do not have an outer membrane defect, but rather a defect in the peptidoglycan layer. Choice D is incorrect because spheroplasts still have peptidoglycan, even though it is defective.

Correct Answer: C

Rationale: The correct answer is C (100°C) because the Koch apparatus is used for sterilization, and the standard temperature for sterilization is 100°C. At this temperature, most microorganisms are killed, making it an effective method for sterilization. Choice A (90°C), B (95°C), and D (110°C) are incorrect because they are not commonly used temperatures for sterilization purposes. Choosing a temperature lower than 100°C may not effectively kill all microorganisms, while choosing a temperature higher than 100°C may lead to unnecessary energy consumption without providing additional sterilization benefits.

Correct Answer: D

Rationale: Interferon is a cell-specific protein that is produced and released from infected cells in response to viral infections. It acts extracellularly to interfere with viral replication, not to inactivate the virus itself. Interferon is not coded for by cellular DNA, but by viral RNA during infection. Therefore, the correct answer, D, is that interferon is not virus-specific but is cell-specific. This is because interferon can be produced by various cell types in response to different types of viral infections, making it a broad-spectrum antiviral defense mechanism.

Correct Answer: A

Rationale: Step 1: Streptococcus mutans is known for its ability to produce lactic acid, which contributes to the demineralization of tooth enamel, leading to dental caries. Step 2: Streptococcus pneumoniae is a common respiratory pathogen and not directly associated with dental caries. Step 3: Bacillus cereus is a foodborne pathogen and not typically found in the oral cavity or associated with dental caries. Step 4: Clostridium tetani causes tetanus, a neurological condition, and is not involved in the formation of dental caries. Summary: Choice A is correct as Streptococcus mutans is specifically linked to dental caries due to its acidogenic and aciduric properties. Choices B, C, and D are incorrect as they are not associated with dental caries.

Correct Answer: A

Rationale: The correct answer is A: Escherichia coli. E. coli typically produces red colonies on Endo agar due to its ability to ferment lactose. This results in the production of acid, causing the colonies to appear red. Salmonella and Shigella are non-lactose fermenters, so they would appear colorless or transparent on Endo agar. Proteus vulgaris is not commonly associated with red colonies on Endo agar. Therefore, based on the characteristic lactose fermentation pattern, E. coli is the most likely microorganism in this scenario.