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A patient with a deep tissue infection had Gram-negative rods isolated from the wound culture. The bacteria were oxidase-positive and non-lactose fermenters. What is the most likely causative agent?
- A. Pseudomonas aeruginosa
- B. Escherichia coli
- C. Klebsiella pneumoniae
- D. Shigella dysenteriae
Correct Answer: A
Rationale: The correct answer is A: Pseudomonas aeruginosa. This is because Pseudomonas is a Gram-negative rod, oxidase-positive, and non-lactose fermenter. These characteristics are typical of Pseudomonas species.
B: Escherichia coli is a Gram-negative rod but is lactose fermenter and usually oxidase-negative.
C: Klebsiella pneumoniae is a Gram-negative rod, non-lactose fermenter, but is usually oxidase-negative.
D: Shigella dysenteriae is a Gram-negative rod, non-lactose fermenter, but is usually oxidase-negative and is more associated with causing shigellosis rather than deep tissue infections.
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For measles virus is true that:
- A. There is no outer membrane
- B. Contains singles-stranded RNA with negative polarity
- C. Belongs to family Togaviridae
- D. Cannot be grown on cell cultures
Correct Answer: B
Rationale: The correct answer is B: Contains single-stranded RNA with negative polarity. Measles virus is an enveloped virus with a single-stranded RNA genome that is negative-sense. This means it must first be transcribed into positive-sense RNA before it can be translated. Choice A is incorrect as the measles virus does have an outer envelope. Choice C is incorrect as measles virus belongs to the family Paramyxoviridae, not Togaviridae. Choice D is incorrect as measles virus can be grown on cell cultures, specifically on Vero cells.
During sanitary and bacteriological examination of air in a drugstore it was revealed that the air had high concentration of sanitary meaningful microorganisms. What microorganisms are these?
- A. Staphylococcus aureus and hemolytic streptococcus
- B. Diphtheritic and tuberculous bacilli
- C. Colibacilli and blue pus bacilli
- D. Epidermal staphylococcus and Sarcina
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
Viruses are characterised by:
- A. They have only one type of nucleic acid
- B. Their extracellular form is referred as “viroidâ€
- C. They are optional intracellular parasites
- D. Their size is measured in micrometers
Correct Answer: A
Rationale: Step 1: Viruses can have either DNA or RNA, not both, hence they have only one type of nucleic acid.
Step 2: The extracellular form of viruses is called virion, not viroid.
Step 3: Viruses are obligate intracellular parasites, meaning they rely on host cells for replication.
Step 4: Viruses are measured in nanometers, not micrometers.
Therefore, the correct answer is A.
Bacteriological laboratory examines canned meat whether it contains botulinum toxin. For this purpose an extract of test specimen and antitoxic antibotulinic serum of A, B, E types were introduced to a group of mice under examination; a control group of mice got the extract without antibotulinic serum. What serological reaction was applied?
- A. Neutralization
- B. Precipitation
- C. Complement binding
- D. Double immune diffusion
Correct Answer: A
Rationale: The correct answer is A: Neutralization. In this scenario, the antibotulinic serum of types A, B, and E were introduced to neutralize the botulinum toxin in the test specimen. The serological reaction applied here involves the neutralization of the toxin by the specific antibodies present in the serum. This process prevents the toxin from causing harm to the mice.
Summary of other choices:
B: Precipitation - This involves the formation of insoluble complexes between antigen and antibody, not the specific neutralization seen in this case.
C: Complement binding - This involves activation of the complement system leading to cell lysis, not the direct neutralization of toxin.
D: Double immune diffusion - This technique is used to determine the presence of specific antibodies or antigens based on their diffusion patterns, not the neutralization of toxin as seen in this scenario.
A patient with a productive cough and fever had a sputum smear revealing Gram-positive cocci in pairs with a capsule. What is the most likely causative agent?
- A. Streptococcus pneumoniae
- B. Klebsiella pneumoniae
- C. Neisseria meningitidis
- D. Staphylococcus aureus
Correct Answer: A
Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is the most likely causative agent based on the description of Gram-positive cocci in pairs with a capsule. S. pneumoniae is known for its characteristic morphology and the presence of a capsule, which helps in evading the immune system. It commonly causes pneumonia, especially in patients with a productive cough and fever.
Incorrect choices:
B: Klebsiella pneumoniae typically presents with a mucoid capsule and is associated with pneumonia in immunocompromised individuals.
C: Neisseria meningitidis is a Gram-negative diplococcus and is more commonly associated with meningitis and septicemia.
D: Staphylococcus aureus is a Gram-positive cocci, but it does not typically present in pairs with a capsule and is more commonly associated with skin and soft tissue infections.