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A patient with a sore throat had a throat culture revealing Gram-positive cocci in chains. The bacteria were catalase-negative and 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.
1. Gram-positive cocci in chains suggest streptococci.
2. Catalase-negative indicates it's not staphylococci.
3. Beta-hemolytic points towards Group A Streptococcus (S. pyogenes).
Summary:
B. Streptococcus pneumoniae is not beta-hemolytic.
C. Enterococcus faecalis is not typically chains.
D. Staphylococcus aureus is catalase-positive.
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Streptococci are:
- A. Gram-positive, short rod shaped bacteria and size 4-6 µm
- B. Gram-negative, rounded or lanceolate shape and size 0,5-1 µm
- C. Gram-negative, short rod shaped bacteria and size 4-6 µm
- D. Gram-positive, spherical or lanceolate shape and size 0,5-1 µm
Correct Answer: D
Rationale: The correct answer is D because Streptococci are Gram-positive bacteria, typically spherical in shape, and range from 0.5-1 µm in size.
A is incorrect as streptococci are not rod-shaped and are usually smaller in size. B is incorrect as they are not Gram-negative and are not typically of such small size.
C is incorrect as streptococci are not Gram-negative and are not usually rod-shaped. Thus, based on their characteristics, the correct answer is D.
The term “zone of inhibition†is used in which of the following procedures?
- A. Use-dilution test
- B. Growth inhibition test
- C. Disk-diffusion test
- D. Multiple inhibition test
Correct Answer: C
Rationale: The correct answer is C: Disk-diffusion test. In the disk-diffusion test, the zone of inhibition refers to the area around an antimicrobial disk where bacterial growth is inhibited. This test is used to determine the susceptibility of bacteria to specific antibiotics. The other choices, such as A: Use-dilution test, B: Growth inhibition test, and D: Multiple inhibition test, do not specifically involve measuring the zone of inhibition and are not commonly used methods for testing antibiotic susceptibility.
A man died from an acute disease characterized by fever, jaundice, hemorrhagic rash, and acute renal insufficiency. Histological examination revealed spiral bacteria shaped like 'C' and 'S' letters. Identify the pathogen.
- A. Leptospira
- B. Treponema
- C. Borrelia
- D. Spirochaeta
Correct Answer: A
Rationale: The correct answer is A: Leptospira. Leptospira is a spiral-shaped bacterium that causes a disease known as leptospirosis, characterized by fever, jajsondice, hemorrhagic rash, and renal insufficiency. The characteristic spiral shape of the bacteria, resembling 'C' and 'S' letters, is a key identifying feature. Leptospira is commonly associated with contaminated water sources and can be transmitted to humans through contact with infected animals or water.
Summary of other choices:
B: Treponema - Treponema pallidum is the causative agent of syphilis, which does not typically present with the combination of symptoms described in the question.
C: Borrelia - Borrelia species are associated with Lyme disease and relapsing fever, but do not match the specific symptoms and histological appearance described in the question.
D: Spirochaeta - Spirochaeta is a genus of bacteria, but specific species within
Anticodon is:
- A. Produced during the process of replication
- B. A nucleotide triplet on the molecule of mRNA
- C. A nucleotide DNA triplet defining the amino acid which has a specific sequence on the polypeptide chain during the translation
- D. A nucleotide triplet forming a unit of genetic code in a transfer RNA molecule corresponding to a complementary codon on messenger RNA
Correct Answer: D
Rationale: The correct answer is D because an anticodon is a nucleotide triplet in a tRNA molecule that pairs with a complementary codon on mRNA during translation. Step 1: Anticodons are found in tRNA, not in DNA or mRNA. Step 2: Anticodons specifically bind to codons on mRNA to ensure correct amino acid incorporation into the growing polypeptide chain, making option D the most accurate choice. Option A is incorrect as replication does not involve anticodons. Option B is incorrect because codons, not anticodons, are found on mRNA molecules. Option C is incorrect as it describes a codon on DNA, not an anticodon on tRNA.
After a prolonged isoniazid treatment, the patient developed polyneuritis, paresthesia, memory disorders, and convulsions. What is the most likely mechanism of the described isoniazid side-effects?
- A. Disruption of cell membrane synthesis
- B. Inhibition of protein synthesis
- C. Inhibition of RNA-synthesis
- D. Inhibition of pyridoxal phosphate synthesis
Correct Answer: D
Rationale: The correct answer is D. Isoniazid inhibits pyridoxal phosphate synthesis, which is the active form of vitamin B6. Pyridoxal phosphate is essential for various enzymatic reactions, including neurotransmitter synthesis and myelin formation. Therefore, isoniazid-induced pyridoxal phosphate deficiency can lead to neurological symptoms like polyneuritis, paresthesia, memory disorders, and convulsions.
A: Disruption of cell membrane synthesis - This is not the mechanism of isoniazid side-effects.
B: Inhibition of protein synthesis - Isoniazid does not directly inhibit protein synthesis.
C: Inhibition of RNA-synthesis - Isoniazid does not inhibit RNA synthesis; it affects vitamin B6 metabolism.