Nokea
The lipopolysaccharides of gram negative bacteria consists of all the following types except:
- A. O-specific polysaccharide chain
- B. R-specific polysaccharide chain
- C. Lipid A
- D. Protoplast
Correct Answer: D
Rationale: The correct answer is D: Protoplast. Lipopolysaccharides of Gram-negative bacteria consist of three main components: O-specific polysaccharide chain, R-specific polysaccharide chain, and Lipid A. Protoplast is not a component of lipopolysaccharides. O-specific polysaccharide chain is responsible for serotype specificity, R-specific polysaccharide chain varies among strains, and Lipid A is the endotoxin component. Protoplast refers to a bacterial cell devoid of a cell wall, which is not a component of lipopolysaccharides.
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Infection of several persons without any epidemiological link is:
- A. Epidemic
- B. Sporadic disease
- C. Endemic
- D. Pandemic
Correct Answer: B
Rationale: The correct answer is B: Sporadic disease. When an infection occurs in several persons without any epidemiological link, it is considered sporadic. This term is used to describe isolated cases that do not form a specific pattern or cluster. It indicates random occurrences and lack of connection between the affected individuals.
A: Epidemic refers to a sudden increase in the number of cases of a disease within a specific population or region, usually linked by a common source or exposure.
C: Endemic signifies the constant presence of a disease within a specific population or region, with cases occurring at a relatively stable rate.
D: Pandemic indicates a global outbreak of a disease affecting a large number of people across multiple countries or continents.
Which of the following has a contact route of transmission
- A. salmonellosis
- B. tularemia
- C. rubella
- D. HIV
Correct Answer: D
Rationale: The correct answer is D: HIV. HIV is transmitted through direct contact with certain body fluids such as blood, semen, vaginal fluids, and breast milk. This direct contact route of transmission makes it different from the other choices. Salmonellosis is typically transmitted through contaminated food or water (not direct contact). Tularemia is usually transmitted through insect bites or contact with infected animals. Rubella is primarily transmitted through respiratory droplets. Therefore, HIV is the only option with a contact route of transmission.
A patient with pneumonia had sputum stained by the Gram method. The smear revealed Gram-positive cocci in pairs with a capsule. What is the most likely causative agent?
- A. Streptococcus pneumoniae
- B. Staphylococcus aureus
- C. Neisseria meningitidis
- D. Klebsiella pneumoniae
Correct Answer: A
Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is a common cause of pneumonia and is known to appear as Gram-positive cocci in pairs with a capsule. The presence of a capsule is a key characteristic of S. pneumoniae. Staphylococcus aureus (B) is a Gram-positive cocci but typically does not have a capsule. Neisseria meningitidis (C) is a Gram-negative diplococcus, not a Gram-positive cocci. Klebsiella pneumoniae (D) is a Gram-negative rod, not a Gram-positive cocci. Therefore, based on the staining pattern and the presence of a capsule, Streptococcus pneumoniae is the most likely causative agent in this case.
The glycocalyx (slime), which is produced in some bacteria, is:
- A. Strongly bound to the cell wall
- B. Involved in the bacterial movement
- C. Weakly bound to the cell wall
- D. None of the above
Correct Answer: C
Rationale: The correct answer is C: Weakly bound to the cell wall. The glycocalyx in bacteria is a protective layer that can be loosely attached to the cell wall or membrane. This loose attachment allows for flexibility and protection against desiccation and immune responses. Choice A is incorrect because the glycocalyx is not strongly bound to the cell wall, as it needs to be able to be shed easily for bacteria to escape host immune responses. Choice B is incorrect because the glycocalyx is not directly involved in bacterial movement, but rather serves as a protective barrier. Choice D is incorrect as the glycocalyx does play a role in bacterial physiology.
A man is being treated for chronic pneumonia for a long time. Microscopy of sputum smears stained using Ziehl-Nielsen method reveals red bacilli 0.25x4 microns in size, located separately or sometimes in small clusters. What disease can be suspected?
- A. Pneumococcal pneumonia
- B. Pulmonary actinomycosis
- C. Pulmonary candidiasis
- D. Pulmonary tuberculosis
Correct Answer: D
Rationale: The correct answer is D: Pulmonary tuberculosis. The presence of red bacilli stained with Ziehl-Nielsen method indicates acid-fast bacteria, which are characteristic of Mycobacterium tuberculosis, the causative agent of tuberculosis. The size and appearance of the bacilli described match those of M. tuberculosis. Chronic pneumonia, along with the specific staining pattern, strongly suggests tuberculosis as the likely diagnosis.
Explanation for other choices:
A: Pneumococcal pneumonia is caused by Streptococcus pneumoniae, which would not show red bacilli on Ziehl-Nielsen staining.
B: Pulmonary actinomycosis is caused by Actinomyces species, not acid-fast bacteria like M. tuberculosis.
C: Pulmonary candidiasis is caused by Candida species, which are fungi and do not appear as red bacilli on staining.