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A patient with abdominal pain had a stool culture revealing non-lactose-fermenting, Gram-negative rods that produced gas in a nutrient broth. What is the most likely causative agent?
- A. Salmonella typhi
- B. Shigella dysenteriae
- C. Escherichia coli
- D. Proteus vulgaris
Correct Answer: D
Rationale: The correct answer is D: Proteus vulgaris. This is because Proteus species are non-lactose-fermenting Gram-negative rods that are known to produce gas in nutrient broths. Proteus vulgaris is commonly associated with urinary tract infections and can also cause abdominal infections.
A: Salmonella typhi typically causes typhoid fever and is not known to produce gas in nutrient broths.
B: Shigella dysenteriae is a causative agent of dysentery and does not typically produce gas in nutrient broths.
C: Escherichia coli is a lactose-fermenting bacterium and does not fit the description of the organism in the stool culture.
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Which of the following bacteria is known for causing Lyme disease?
- A. Borrelia burgdorferi
- B. Clostridium difficile
- C. Streptococcus pneumoniae
- D. Mycobacterium tuberculosis
Correct Answer: A
Rationale: The correct answer is A: Borrelia burgdorferi. This bacterium is known for causing Lyme disease, which is transmitted through tick bites. Borrelia burgdorferi is specifically associated with Lyme disease due to its ability to infect and spread within the body, leading to a range of symptoms if left untreated.
Summary of incorrect choices:
B: Clostridium difficile - Known for causing gastrointestinal infections, not Lyme disease.
C: Streptococcus pneumoniae - Commonly causes pneumonia and other respiratory infections, not Lyme disease.
D: Mycobacterium tuberculosis - Causes tuberculosis, a respiratory disease, not Lyme disease.
A sputum sample from a patient with pneumonia revealed Gram-positive cocci in pairs with a capsule. What is the most likely causative agent?
- A. Streptococcus pneumoniae
- B. Staphylococcus aureus
- C. Klebsiella pneumoniae
- D. Pseudomonas aeruginosa
Correct Answer: A
Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is the most likely causative agent for pneumonia in this case due to the presence of Gram-positive cocci in pairs with a capsule, which is a typical characteristic of S. pneumoniae. This pathogen is a common cause of community-acquired pneumonia and is known for its encapsulated morphology. Staphylococcus aureus (B) is a Gram-positive cocci but does not typically present in pairs with a capsule in pneumonia cases. Klebsiella pneumoniae (C) is a Gram-negative bacterium and does not match the description provided. Pseudomonas aeruginosa (D) is a Gram-negative bacterium that is not typically associated with Gram-positive cocci in pneumonia samples.
Microorganisms of various species are often organized into complex communities on a surface and are called __________.
- A. colonies
- B. biofilms
- C. ecosystems
- D. plagues
Correct Answer: B
Rationale: The correct answer is B: biofilms. Biofilms are structured communities of microorganisms that adhere to a surface and are embedded in a matrix. This is the most appropriate term as it specifically describes the organization of various species into complex communities on a surface. Colonies (A) refer to groups of cells of the same species, not necessarily multiple species. Ecosystems (C) are broader systems involving interactions between living organisms and their environment. Plagues (D) are outbreaks of disease, not a term used to describe organized microbial communities.
A woman who was infected with toxoplasmosis during the pregnancy has a child with multiple congenital defects. This is a result of:
- A. Teratogenesis
- B. Cancerogenesis
- C. Recombination
- D. Chemical mutogenesis
Correct Answer: A
Rationale: The correct answer is A: Teratogenesis. Teratogenesis refers to the process of abnormal development of the fetus leading to congenital defects due to exposure to harmful agents during pregnancy. In this case, toxoplasmosis infection during pregnancy can lead to teratogenesis, causing multiple congenital defects in the child. Other choices are incorrect because B: Cancerogenesis refers to the process of cancer formation, C: Recombination is a genetic process unrelated to congenital defects, and D: Chemical mutagenesis refers to mutations caused by chemical agents, not necessarily congenital defects.
Which toxin is specific for ETEC:
- A. TSST-1
- B. Shiga-like toxin
- C. Erythrogenic toxin
- D. LT enterotoxin
Correct Answer: D
Rationale: The correct answer is D: LT enterotoxin. This toxin is specific for Enterotoxigenic E. coli (ETEC) and is responsible for causing diarrhea by increasing cyclic AMP levels in intestinal cells. TSST-1 (choice A) is produced by Staphylococcus aureus, not ETEC. Shiga-like toxin (choice B) is produced by Shigella and EHEC, not ETEC. Erythrogenic toxin (choice C) is produced by Streptococcus pyogenes, not ETEC. Therefore, the LT enterotoxin is the specific toxin associated with ETEC.