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Which of the following is a major characteristic of Gram-negative bacteria?
- A. Thick peptidoglycan layer
- B. Outer membrane with lipopolysaccharides
- C. Absence of a cell wall
- D. Presence of teichoic acids
Correct Answer: B
Rationale: The correct answer is B: Outer membrane with lipopolysaccharides. Gram-negative bacteria have an outer membrane that contains lipopolysaccharides, which play a role in pathogenicity and resistance to certain antibiotics. This outer membrane is a distinguishing feature of Gram-negative bacteria, as opposed to Gram-positive bacteria that have a thick peptidoglycan layer. Choices A, C, and D are incorrect because Gram-negative bacteria have a thin peptidoglycan layer, do have a cell wall (although it is different from Gram-positive bacteria), and do not contain teichoic acids.
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An outbreak of food poisoning was recorded in an urban settlement. The illness was diagnosed as botulism on the grounds of clinical presentations. What foodstuffs should be chosen for analysis in the first place in order to confirm the diagnosis?
- A. Tinned food
- B. Potatoes
- C. Pasteurized milk
- D. Boiled meat
Correct Answer: A
Rationale: The correct answer is A: Tinned food. Botulism is often caused by the botulinum toxin produced by the bacterium Clostridium botulinum, which can be present in improperly canned foods. Analyzing tinned food allows for direct detection of the toxin or bacteria, confirming the diagnosis. Potatoes, pasteurized milk, and boiled meat are less likely sources of botulism compared to tinned food, making them less suitable for initial analysis in this case.
Giardiasis is a waterborne gastrointestinal disease caused by Giardia intestinalis, which is a:
- A. protozoan
- B. bacterium
- C. fungus
- D. virus
Correct Answer: A
Rationale: Step 1: Giardiasis is caused by Giardia intestinalis, which is a well-known protozoan parasite.
Step 2: Protozoans are single-celled eukaryotic organisms commonly found in water sources.
Step 3: Giardia intestinalis infects the intestine, causing symptoms like diarrhea and abdominal cramps.
Step 4: Bacteria (Choice B) are prokaryotic organisms, different from protozoans.
Step 5: Fungi (Choice C) are also eukaryotic but are not responsible for causing Giardiasis.
Step 6: Viruses (Choice D) are not cellular and cannot independently cause Giardiasis.
In summary, the correct answer is A (protozoan) because Giardia intestinalis is a protozoan parasite specifically known to cause Giardiasis, while the other choices (Bacterium, Fungus, Virus) do not match the characteristics of the
A fetus infected with rubella virus produces which of the following antibodies that can then be detected in the umbilical cord?
- A. IgA
- B. IgM
- C. IgG
- D. IgD
Correct Answer: B
Rationale: The correct answer is B: IgM. IgM antibodies are the first type of antibodies produced in response to an infection, indicating an active or recent infection. In the case of a rubella virus infection in a fetus, IgM antibodies can be detected in the umbilical cord blood, confirming the presence of the virus. IgA antibodies are mainly found in mucosal areas, IgG antibodies indicate past infection or immunity, and IgD antibodies play a role in B cell activation but are not typically detected in this context.
Lytic cycle of the bacteriophages differs from the lysogenic one by
- A. lysogenetic phages destroy the host cell when leaving the cell
- B. lytic phages do not destroy the host cell
- C. do not differ
- D. none of them
Correct Answer: A
Rationale: The correct answer is A because in the lytic cycle, the bacteriophage destroys the host cell upon release, whereas in the lysogenic cycle, the phage integrates its DNA into the host genome without killing the host immediately. This integration may lead to the destruction of the host cell at a later stage. Choice B is incorrect as lytic phages do destroy the host cell. Choice C is incorrect as the two cycles have distinct mechanisms. Choice D is incorrect as there are clear differences between the lytic and lysogenic cycles.
A laboratory received a sample of water used in drug production for sanitary and viral analysis. What group of viruses will indicate fecal contamination of water and thus the need for its additional purification?
- A. Picornaviridae
- B. Herpesviridae
- C. Flaviviridae
- D. Retroviridae
Correct Answer: A
Rationale: The correct answer is A: Picornaviridae. Picornaviruses, such as enteroviruses, are commonly found in the feces of infected individuals. Therefore, their presence in water indicates fecal contamination and the need for additional purification.
B: Herpesviridae are not typically associated with fecal contamination.
C: Flaviviridae are mainly transmitted through arthropods like mosquitoes, not fecal contamination.
D: Retroviridae, including HIV, are not typically excreted in high levels in feces and are not indicators of fecal contamination.