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A fecal sample from a patient with diarrhea was cultured on Endo agar, resulting in colorless colonies. The bacteria were Gram-negative rods. What microorganism is most likely?
- A. Salmonella
- B. Shigella
- C. Escherichia coli
- D. Proteus
Correct Answer: B
Rationale: The correct answer is B: Shigella. On Endo agar, Shigella appears as colorless colonies due to its inability to ferment lactose. Shigella is a Gram-negative rod and is a common cause of diarrhea. Salmonella (A) and Escherichia coli (C) would typically produce pink colonies on Endo agar as they can ferment lactose. Proteus (D) is not commonly associated with diarrhea and would not be expected to grow on Endo agar.
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The virulence factors of bacteria include:
- A. size, adhesion, resistance, and mutation
- B. colonization, invasion, toxins, and adhesion
- C. toxins, evasion of body defenses, motility, and size
- D. colonization, chemotaxis, fermentation, and toxins
Correct Answer: B
Rationale: Rationale: The correct answer is B because virulence factors of bacteria are characteristics that enable them to cause disease. Colonization allows bacteria to establish and multiply in the host. Invasion refers to the ability to penetrate host tissues. Toxins are substances produced by bacteria that harm the host. Adhesion is crucial for bacteria to attach to host cells.
A: Size and mutation are not typical virulence factors. Resistance is not directly related to causing disease.
C: While toxins and evasion of body defenses are correct, motility and size are not universally considered virulence factors.
D: Chemotaxis and fermentation are not primary virulence factors, unlike colonization and toxins.
Etiological cause of bacteremia could be:
- A. S.epidermidis, E.coli, S. aureus
- B. P.aeruginosa, K. pneumoniae, E.coli
- C. Resident skin diphtheroids
- D. All of the above
Correct Answer: D
Rationale: The correct answer is D because bacteremia can be caused by a variety of bacteria including S.epidermidis, E.coli, S.aureus, P.aeruginosa, K.pneumoniae, and resident skin diphtheroids. Bacteremia refers to the presence of bacteria in the bloodstream, which can occur due to infections from various sources. Choices A and B include common bacteria known to cause bacteremia, while choice C refers to resident skin diphtheroids that can also enter the bloodstream under certain conditions. Therefore, the correct answer is D as it encompasses all the possible etiological causes of bacteremia.
Which of the following bacteria can produce endotoxins that cause septic shock?
- A. Escherichia coli
- B. Salmonella enterica
- C. Pseudomonas aeruginosa
- D. All of the above
Correct Answer: D
Rationale: The correct answer is D because all of the mentioned bacteria (Escherichia coli, Salmonella enterica, and Pseudomonas aeruginosa) are gram-negative bacteria that produce endotoxins in their cell walls. Endotoxins are released when the bacteria are destroyed, leading to the activation of the immune system and potentially causing septic shock. Escherichia coli and Salmonella enterica are common causes of gastrointestinal infections, while Pseudomonas aeruginosa is known for causing infections in immunocompromised individuals. Therefore, all three bacteria can produce endotoxins that contribute to septic shock. Choices A, B, and C are incorrect because each of these bacteria individually can produce endotoxins that lead to septic shock.
A wound culture grew Gram-negative rods that were oxidase-positive and lactose non-fermenters. What is the most likely microorganism?
- A. Pseudomonas aeruginosa
- B. Escherichia coli
- C. Salmonella typhi
- D. Shigella dysenteriae
Correct Answer: A
Rationale: The correct answer is A: Pseudomonas aeruginosa. P. aeruginosa is a Gram-negative rod that is oxidase-positive and lactose non-fermenting. The positive oxidase test indicates the presence of cytochrome c oxidase, a characteristic of P. aerugin. E. coli is lactose fermenting. Salmonella and Shigella are also Gram-negative rods, but they are lactose fermenters, unlike the lactose non-fermenting P. aeruginosa.
A patient with a sore throat and fever 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.
1. Gram-positive cocci in chains suggest streptococci.
2. Beta-hemolytic activity indicates Streptococcus pyogenes.
3. Streptococcus pyogenes is commonly associated with sore throat (pharyngitis) and fever.
4. Streptococcus pneumoniae (choice B) is alpha-hemolytic and mainly causes pneumonia.
5. Enterococcus faecalis (choice C) is not typically associated with sore throat.
6. Staphylococcus aureus (choice D) is not commonly beta-hemolytic and is not a typical cause of pharyngitis.