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A smear from a sore throat revealed rod-shaped bacteria with polar granules. What is the most likely causative agent?
- A. Corynebacterium diphtheriae
- B. Streptococcus pneumoniae
- C. Haemophilus influenzae
- D. Klebsiella pneumoniae
Correct Answer: A
Rationale: The most likely causative agent is Corynebacterium diphtheriae. Step 1: Presence of rod-shaped bacteria indicates a bacillus. Step 2: Polar granules suggest metachromatic granules seen in C. diphtheriae. Step 3: C. diphtheriae causes diphtheria, which presents with sore throat. Summary: B is incorrect as S. pneumoniae is a cocci, not a bacillus. C is incorrect as H. influenzae is a pleomorphic coccobacillus. D is incorrect as K. pneumoniae is a large, encapsulated bacillus.
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A blood culture from a patient with sepsis revealed Gram-positive cocci in clusters. The bacteria were catalase-positive and coagulase-negative. What is the most likely causative agent?
- A. Staphylococcus epidermidis
- B. Staphylococcus aureus
- C. Streptococcus pyogenes
- D. Enterococcus faecalis
Correct Answer: A
Rationale: The correct answer is A: Staphylococcus epidermidis. This is supported by the characteristics of Gram-positive cocci in clusters, catalase-positive, and coagulase-negative. Staphylococcus epidermidis fits all these criteria, as it is a common skin commensal that can cause infections in immunocompromised individuals. Staphylococcus aureus (choice B) is catalase-positive and coagulase-positive. Streptococcus pyogenes (choice C) is catalase-negative. Enterococcus faecalis (choice D) is catalase-negative and not typically seen in clusters. Therefore, based on the given information, Staphylococcus epidermidis is the most likely causative agent.
Which bacterium is known as a common cause of hospital-acquired infections?
- A. Clostridium botulinum
- B. Staphylococcus aureus
- C. Treponema pallidum
- D. Mycobacterium leprae
Correct Answer: B
Rationale: The correct answer is B: Staphylococcus aureus. This bacterium is known as a common cause of hospital-acquired infections due to its ability to colonize the skin and mucous membranes of healthcare workers and patients. Staphylococcus aureus can cause various infections, including surgical site infections and bloodstream infections, in healthcare settings.
Rationale:
1. Clostridium botulinum is known for causing foodborne botulism, not hospital-acquired infections.
2. Treponema pallidum causes syphilis, which is primarily transmitted through sexual contact, not hospital settings.
3. Mycobacterium leprae causes leprosy, which is not commonly associated with hospital-acquired infections.
In summary, Staphylococcus aureus is the correct answer as it is a common cause of hospital-acquired infections due to its prevalence in healthcare environments, unlike the other choices which are not typically associated with hospital-acquired infections.
Which of the following is a host-dependent bacterium?
- A. Mycoplasma
- B. Ureaplasma
- C. Rickettsia
- D. Micrococcus
Correct Answer: C
Rationale: The correct answer is C: Rickettsia. Rickettsia is a host-dependent bacterium because it requires living cells of a host organism to survive and replicate. This bacterium is an obligate intracellular pathogen, meaning it cannot grow outside of a host cell.
A: Mycoplasma and B: Ureaplasma are not host-dependent as they can grow and reproduce in cell-free environments due to possessing their own unique cell wall structures.
D: Micrococcus is a free-living bacterium that can survive and reproduce independently without relying on a host organism.
Examination of duodenal contents revealed some pyriform protozoa with twin nuclei and four pairs of flagella. There were two supporting filaments between the nuclei and a suctorial disc on the ventral side. What representative of protozoa was revealed in this patient?
- A. Lamblia
- B. Toxoplasma
- C. Leishmania
- D. Intestinal trichomonad
Correct Answer: A
Rationale: Rationale for Correct Answer A (Lamblia):
1. Pyriform protozoa with twin nuclei, four pairs of flagella, and a suctorial disc match the characteristics of Giardia lamblia.
2. The presence of two supporting filaments between the nuclei is a unique feature of Giardia lamblia.
3. Giardia lamblia is known to infect the duodenum and cause symptoms such as diarrhea and abdominal pain.
Summary of Incorrect Choices:
B: Toxoplasma - Toxoplasma gondii is not characterized by four pairs of flagella or supporting filaments in the nuclei.
C: Leishmania - Leishmania species do not typically have the described morphology or location in the duodenum.
D: Intestinal trichomonad - Intestinal trichomonads do not exhibit the specific features mentioned in the question, such as twin nuclei and supporting filaments.
Which staining method is used for proving the formation of spores
- A. Klett and Gins
- B. Ziehl-Neelsen
- C. Gram and Loeffler's
- D. Moeller
Correct Answer: D
Rationale: The correct answer is D: Moeller. Moeller staining method is specifically designed to detect spores due to its ability to differentiate between the spore and the vegetative cell. It involves applying multiple stains such as malachite green, safranin, and heat to visualize the endospore structure. This method is essential for proving the formation of spores as it highlights the resistant spore structures within the bacterial cell.
A: Klett and Gins is not used for spore staining.
B: Ziehl-Neelsen is used for acid-fast staining, not spore staining.
C: Gram and Loeffler's are used for gram staining, not spore staining.