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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 on blood agar. What is the most likely causative agent?
- A. Streptococcus pyogenes
- B. Staphylococcus aureus
- C. Streptococcus pneumoniae
- D. Enterococcus faecalis
Correct Answer: A
Rationale: Step 1: Gram-positive cocci in chains suggest Streptococcus species.
Step 2: Catalase-negative eliminates Staphylococcus aureus.
Step 3: Beta-hemolytic on blood agar matches Streptococcus pyogenes.
Step 4: Streptococcus pyogenes is a common cause of sore throat (pharyngitis).
Summary:
A: Streptococcus pyogenes - Correct due to Gram-positive cocci in chains, catalase-negative, beta-hemolytic, and common cause of sore throat.
B: Staphylococcus aureus - Incorrect due to catalase-positive.
C: Streptococcus pneumoniae - Incorrect due to alpha-hemolytic.
D: Enterococcus faecalis - Incorrect due to not being beta-hemolytic.
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A source of hospital-acquired infection could be:
- A. New patients in incubation period
- B. Medical staff
- C. Medical instruments
- D. All are correct
Correct Answer: D
Rationale: The correct answer is D because all the choices can contribute to hospital-acquired infections. New patients in the incubation period can spread infections, medical staff can inadvertently transmit infections, and contaminated medical instruments can also be a source of infections. Therefore, it is important to consider all these factors to prevent and control the spread of infections in a hospital setting.
What reaction is catalyzed by a beta-lactamase enzyme
- A. the final cross-linking reaction to form the bacterial cell wall
- B. the biosynthesis of the penicillin structure from the amino acid valine and cysteine
- C. the hydrolysis of the four-membered ring present in penicillin
- D. the hydrolysis of the acyl side chain from penicillin structures
Correct Answer: C
Rationale: The correct answer is C: the hydrolysis of the four-membered ring present in penicillin. Beta-lactamase enzyme catalyzes the hydrolysis of the four-membered beta-lactam ring present in penicillin, rendering the antibiotic ineffective against bacterial cell walls. This enzyme breaks the bond in the beta-lactam ring, thus inactivating the antibiotic.
Incorrect choices:
A: the final cross-linking reaction to form the bacterial cell wall - This is incorrect as beta-lactamase does not participate in the formation of bacterial cell walls.
B: the biosynthesis of the penicillin structure from the amino acid valine and cysteine - This is incorrect as beta-lactamase is not involved in the biosynthesis of penicillin.
D: the hydrolysis of the acyl side chain from penicillin structures - This is incorrect as beta-lactamase specifically targets the beta-lactam ring, not the
Salmonellosis is caused by:
- A. Salmonella typhi
- B. Salmonella enteritidis
- C. Shigella flexneri
- D. None of the above
Correct Answer: B
Rationale: The correct answer is B: Salmonella enteritidis. Salmonellosis is typically caused by Salmonella species, with Salmonella enteritidis being one of the common culprits. Salmonella typhi causes typhoid fever, not salmonellosis. Shigella flexneri is responsible for causing shigellosis, a different bacterial infection. Choosing "None of the above" is incorrect as Salmonella enteritidis is a known cause of salmonellosis.
A 3 month old infant has got a white deposition on the mucous membrane of his mouth, tongue and lips. The doctor suspected candidosis. What nutrient medium should be used for inoculation of the material under examination in order to confirm this diagnosis?
- A. Sabouraud
- B. Endo
- C. Loewenstein-Jensen
- D. Roux
Correct Answer: A
Rationale: The correct answer is A: Sabouraud. Sabouraud agar is specifically designed for the cultivation of fungi and yeasts, making it ideal for identifying Candida species causing candidosis. It contains antibiotics to inhibit bacterial growth, promoting the growth of fungi. Endo, Loewenstein-Jensen, and Roux are not suitable for fungal cultures and are used for different purposes like bacterial isolation or mycobacterial cultures. Sabouraud agar is the best choice for confirming candidosis due to its fungal-selective properties.
What is the function of bacterial fimbriae?
- A. Adhesion to surfaces
- B. DNA replication
- C. Protein synthesis
- D. Flagella movement
Correct Answer: A
Rationale: The correct answer is A: Adhesion to surfaces. Bacterial fimbriae are hair-like appendages that help bacteria attach to surfaces, such as host cells or medical devices. This adhesion is crucial for colonization and infection. DNA replication (B) occurs in the cell's nucleus, not on the surface. Protein synthesis (C) happens inside the cell, not on the fimbriae. Flagella movement (D) is the function of flagella, not fimbriae.