Nokea
Which of the following is a characteristic feature of Gram-positive bacteria?
- A. Outer membrane
- B. Thin peptidoglycan layer
- C. Thick peptidoglycan layer
- D. Presence of LPS
Correct Answer: C
Rationale: The correct answer is C: Thick peptidoglycan layer. Gram-positive bacteria have a thick peptidoglycan layer in their cell wall, which retains the crystal violet stain during Gram staining. This thick layer is a key characteristic feature that helps differentiate Gram-positive bacteria from Gram-negative bacteria.
Rationale:
1. Gram-positive bacteria retain the crystal violet stain due to their thick peptidoglycan layer.
2. This thick layer provides structural support and protection to the cell.
3. Gram-positive bacteria lack an outer membrane, which is a feature of Gram-negative bacteria (Choice A).
4. Thin peptidoglycan layer is a characteristic of Gram-negative bacteria, not Gram-positive (Choice B).
5. Presence of LPS (lipopolysaccharide) is a feature of Gram-negative bacteria, not Gram-positive (Choice D).
In summary, the presence of a thick peptidoglycan layer is a characteristic feature of Gram-positive
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Microscopic analysis of a smear stained by Ziehl-Neelsen method revealed bright red bacilli. What microorganism is being tested for?
- A. Mycobacterium tuberculosis
- B. Staphylococcus aureus
- C. Clostridium tetani
- D. Escherichia coli
Correct Answer: A
Rationale: The Ziehl-Neelsen stain is specific for acid-fast bacteria like Mycobacterium tuberculosis. The bright red bacilli seen in the smear indicate the presence of acid-fast organisms, which is characteristic of Mycobacterium tuberculosis. Staphylococcus aureus, Clostridium tetani, and Escherichia coli are not acid-fast bacteria and would not be stained red using the Ziehl-Neelsen method. Therefore, the correct answer is A: Mycobacterium tuberculosis.
A patient with a severe sore throat had a throat culture revealing Gram-positive cocci in chains. The bacteria were beta-hemolytic. What is the most likely causative agent?
- A. Streptococcus pyogenes
- B. Streptococcus pneumoniae
- C. Enterococcus faecalis
- D. Staphylococcus aureus
Correct Answer: A
Rationale: The correct answer is A: Streptococcus pyogenes. This bacterium is the most likely causative agent due to its characteristic features. Streptococcus pyogenes is Gram-positive cocci in chains, which matches the description provided in the question. It is also known to be beta-hemolytic, causing complete lysis of red blood cells on blood agar. Streptococcus pyogenes is a common pathogen causing sore throat, often associated with pharyngitis.
Explanation for incorrect choices:
B: Streptococcus pneumoniae - This bacterium is Gram-positive but usually occurs in pairs (diplococci) and is alpha-hemolytic.
C: Enterococcus faecalis - This bacterium is Gram-positive cocci but is not typically beta-hemolytic and is not commonly associated with sore throat infections.
D: Staphylococcus aureus - This bacterium is Gram-positive cocci but usually occurs in clusters and
Basing upon the data of laboratory assessment of sanitary state of soil in a certain territory, the soil was found to be low-contaminated according to the sanitary indicative value; contaminated according to the coli titer; low-contaminated according to the anaerobe titer (Cl. perfringens). This is indicative of:
- A. Fresh fecal contamination
- B. Old fecal contamination
- C. Insufficient intensity of soil humification
- D. Constant entry of organic protein contaminations
Correct Answer: A
Rationale: Step 1: The soil is low-contaminated according to the sanitary indicative value, which indicates that the contamination is recent.
Step 2: The soil is contaminated according to coli titer, suggesting the presence of coliform bacteria typically found in fresh fecal matter.
Step 3: The soil is low-contaminated according to the anaerobe titer (Cl. perfringens), which is an indicator of recent fecal contamination.
Step 4: Based on the above steps, the correct answer is A: Fresh fecal contamination, as the presence of coliform bacteria and recent anaerobe titer levels point to recent fecal contamination.
Summary:
B: Old fecal contamination - Incorrect because the indicators suggest recent contamination.
C: Insufficient intensity of soil humification - Incorrect as it is not related to the specific indicators mentioned in the question.
D: Constant entry of organic protein contaminations - Incorrect as the indicators point towards fecal contamination, not protein
A 40 year old man noticed a reddening and an edema of skin in the area of his neck that later developed into a small abscess. The incised focus is dense, yellowish-green. The pus contains white granules. Histological examination revealed drusen of a fungus, plasmatic and xanthome cells, macrophages. What type of mycosis is the most probable?
- A. Actinomycosis
- B. Aspergillosis
- C. Candidosis
- D. Sporotrichosis
Correct Answer: D
Rationale: The correct answer is D: Sporotrichosis. Sporotrichosis is caused by the fungus Sporothrix schenckii, which commonly presents as a subcutaneous infection. In the given case, the presence of a small abscess with yellowish-green pus containing white granules is indicative of sporotrichosis. The histological examination showing drusen of a fungus, plasmatic and xanthome cells, and macrophages further supports the diagnosis of sporotrichosis.
Choice A: Actinomycosis is a bacterial infection caused by Actinomyces species, not a fungal infection.
Choice B: Aspergillosis is caused by Aspergillus species and typically presents as a pulmonary infection, not a subcutaneous abscess as described in the case.
Choice C: Candidosis is caused by Candida species and usually presents as mucocutaneous infections, not a subcutaneous abscess with the
The specific prevention (by vaccination) of the disease gas gangrene (caused by Clostridium perfringens) is based on:
- A. Killed whole cell vaccine
- B. Anatoxin
- C. There is no specific prevention by vaccination
- D. Alive attenuated vaccine
Correct Answer: B
Rationale: The correct answer is B: Anatoxin. An anatoxin is a toxin that has been rendered harmless while retaining its ability to stimulate an immune response. Gas gangrene is caused by the toxins produced by Clostridium perfringens, not the bacteria itself. Therefore, vaccination with an anatoxin can trigger the immune system to produce antibodies against the toxin, providing immunity against the disease.
A: Killed whole cell vaccine - Gas gangrene is caused by toxins, not the whole bacterium. This type of vaccine may not be effective in preventing the disease.
C: There is no specific prevention by vaccination - This is incorrect, as vaccination with an anatoxin can prevent gas gangrene.
D: Alive attenuated vaccine - Attenuated vaccines contain live, weakened forms of the pathogen. However, for gas gangrene prevention, targeting the specific toxin with an anatoxin vaccine is more appropriate.