Nokea
During bacteriological examination of sputum of a child with choking cough and fever there were revealed glossy smooth colonies growing on casein-charcoal agar and reminding of mercury drops. Microscopic examination revealed short Gram-negative bacteria. What microorganism was secured from the sputum?
- A. Bordetella pertussis
- B. Haemophylus influenzae
- C. Corynebacterium dyphtheriae
- D. Klebsiella pneumoniae
Correct Answer: A
Rationale: The correct answer is A: Bordetella pertussis. Glossy smooth colonies growing on casein-charcoal agar resembling mercury drops indicate Bordetella pertussis, the causative agent of whooping cough. The presence of short Gram-negative bacteria further supports this identification. Option B, Haemophilus influenzae, typically grows as small, round, translucent colonies on chocolate agar. Option C, Corynebacterium diphtheriae, forms gray colonies on tellurite agar. Option D, Klebsiella pneumoniae, appears as mucoid colonies on MacConkey agar.
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The tool of choice to observe living microorganisms is the
- A. bright-field microscope
- B. phase-contrast microscope
- C. fluorescence microscope
- D. electron microscope
Correct Answer: B
Rationale: The correct answer is B: phase-contrast microscope. This type of microscope is ideal for observing living microorganisms because it enhances the contrast of transparent specimens without the need for staining or fixing, allowing for clear visualization of internal structures and movements. Bright-field microscopes (A) are suitable for observing fixed and stained specimens, not living organisms. Fluorescence microscopes (C) are used to detect specific cellular components tagged with fluorescent markers, not ideal for observing overall morphology. Electron microscopes (D) use electron beams and are best for viewing detailed structures at high magnification, but are not suitable for observing living organisms due to the need for vacuum conditions.
Laboratory diagnosis of Rotavirus infection includes
- A. Egg inoculation
- B. Sensitive laboratory animals
- C. Ascoli test
- D. Cell cultures
Correct Answer: D
Rationale: The correct answer is D: Cell cultures. Rotavirus diagnosis involves detecting viral antigens in stool samples using cell cultures. Cell cultures allow for the replication of the virus, facilitating its identification. A: Egg inoculation and B: Sensitive laboratory animals are not commonly used for Rotavirus diagnosis due to ethical concerns and practical limitations. C: Ascoli test is used for detecting specific proteins in serum, not for Rotavirus detection in stool samples. In summary, cell cultures are the most appropriate method for laboratory diagnosis of Rotavirus infection due to their ability to support viral replication and antigen detection.
Enzymes used in ELISA are those except:
- A. Î’-lactamase
- B. Alkaline phosphatase
- C. Horseradish peroxidase
- D. Î’- galactosidase
Correct Answer: A
Rationale: The correct answer is A: Β-lactamase. In ELISA, enzymes like alkaline phosphatase, horseradish peroxidase, and Β-galactosidase are commonly used as labels to detect the presence of specific molecules. Β-lactamase is not typically used in ELISA as it is an enzyme used to hydrolyze β-lactam antibiotics. Therefore, it does not serve the purpose of detecting specific molecules in ELISA. Alkaline phosphatase, horseradish peroxidase, and Β-galactosidase are preferred enzymes in ELISA due to their ability to produce a detectable signal when bound to specific molecules.
The number of new cases of a disease over a certain period of time compared with the general healthy population is referred to as:
- A. incidence
- B. prevalence
- C. virulence
- D. mortality
Correct Answer: A
Rationale: The correct answer is A: incidence. Incidence refers to the number of new cases of a disease occurring within a specific time period in relation to the healthy population. It helps in understanding the risk of developing the disease. Prevalence (B) is the total number of existing cases at a given point in time. Virulence (C) is the severity of the disease once contracted. Mortality (D) refers to the number of deaths due to the disease, not the new cases. Therefore, the correct term for new cases is incidence.
Transduction is:
- A. Transformation
- B. Transfer of genetic material between donor and recipient bacterial cells with the help of latent phage
- C. Transfer of large plasmids from a donor cell to a recipient cell
- D. None of the above
Correct Answer: B
Rationale: Transduction is the transfer of genetic material between bacterial cells with the help of a phage (virus). This process involves a phage infecting a bacterial cell, replicating inside it, and then transferring bacterial DNA along with phage DNA to another bacterial cell. This is different from transformation (choice A) which involves the uptake of naked DNA by a bacterial cell and plasmid transfer (choice C) which involves the transfer of small, circular DNA molecules. Therefore, the correct answer is B because it specifically describes the process of transduction in bacteria, while choices A and C describe different mechanisms of genetic transfer.