A patient with a wound infection had a Gram-positive cocci isolated from the sample. The bacteria were catalase-positive and coagulase-positive. What is the likely causative agent?

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Question 1 of 9

A patient with a wound infection had a Gram-positive cocci isolated from the sample. The bacteria were catalase-positive and coagulase-positive. What is the likely causative agent?

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus aureus. This is because Staphylococcus aureus is Gram-positive, catalase-positive, and coagulase-positive, which matches the characteristics described in the question. Staphylococcus epidermidis is also Gram-positive but is coagulase-negative. Streptococcus pneumoniae is Gram-positive but is catalase-negative. Enterococcus faecalis is Gram-positive but is catalase-negative and coagulase-negative. Therefore, based on the given information, Staphylococcus aureus is the likely causative agent of the wound infection.

Question 2 of 9

The bacterial species that is resistant to novobiocin is:

Correct Answer: C

Rationale: The correct answer is C: Staphylococcus saprophyticus. The rationale is that Staphylococcus saprophyticus is the only one among the listed species that is known to be resistant to novobiocin. This resistance is due to the specific mechanism of action of novobiocin, which targets DNA gyrase, and Staphylococcus saprophyticus possesses an altered DNA gyrase enzyme that renders it resistant to the antibiotic. Staphylococcus aureus and Staphylococcus epidermidis are susceptible to novobiocin, making choices A and B incorrect. Choice D, "none of the listed," is also incorrect as Staphylococcus saprophyticus is indeed resistant to novobiocin.

Question 3 of 9

A microscope that provides a three-dimensional image of a specimen is a

Correct Answer: D

Rationale: The correct answer is D: scanning electron microscope. A scanning electron microscope provides a three-dimensional image of a specimen by scanning a focused electron beam across the surface of the specimen, detecting the electrons that are emitted from the surface, and creating a detailed image. This is achieved through the detection of secondary electrons, backscattered electrons, and X-rays emitted from the specimen surface. A dark-field microscope (choice A) utilizes oblique lighting to enhance contrast and is not specifically designed to provide a 3D image. A transmission electron microscope (choice B) uses a beam of electrons transmitted through a specimen to create a 2D image at high magnification. A bright-field microscope (choice C) is a basic microscope that illuminates a specimen with uniform light and does not provide a 3D image like a scanning electron microscope does.

Question 4 of 9

Which of the following bacteria are capable of surviving in both aerobic and anaerobic environments?

Correct Answer: B

Rationale: The correct answer is B: Facultative anaerobes. Facultative anaerobes can survive in both aerobic and anaerobic environments. In aerobic conditions, they use oxygen for energy production, while in anaerobic conditions, they can switch to fermentation or anaerobic respiration. A: Obligate aerobes require oxygen to survive and cannot survive in anaerobic environments. C: Obligate anaerobes cannot survive in the presence of oxygen and only thrive in anaerobic conditions. D: Microaerophiles require low levels of oxygen to survive and cannot thrive in fully aerobic or anaerobic conditions.

Question 5 of 9

Urinalysis of a patient with acute cystitis shows leukocytes and a large number of gram-negative bacilli. Inoculation has resulted in the growth of mucous colonies that produce a green soluble pigment. What microorganism is the most likely cause of the patient's disorder?

Correct Answer: C

Rationale: The correct answer is C: Escherichia coli. E. coli is the most common cause of acute cystitis. It typically presents with leukocytes and gram-negative bacilli in the urine. The green pigment production indicates pyocyanin, which is a characteristic of E. coli. Pseudomonas aeruginosa (A) can also produce green pigment, but it is less common in urinary tract infections. Proteus mirabilis (B) is associated with a swarming motility pattern on agar, not mucous colonies. Klebsiella pneumoniae (D) is associated with pneumonia and other respiratory infections, not cystitis.

Question 6 of 9

A subacute toxic effect occurs when the adverse drug effect occurs:

Correct Answer: C

Rationale: The correct answer is C: after repeated exposure for days. Subacute toxic effects typically manifest after a period of time that is longer than immediate (A) or acute (B) effects but shorter than chronic effects (D). This duration of days aligns with the definition of subacute, which refers to effects that occur gradually over a relatively short time frame. It is important to differentiate between the timing of toxic effects to accurately assess the potential harm caused by a substance. Choices A, B, and D are incorrect because they do not align with the characteristic time frame associated with subacute toxic effects.

Question 7 of 9

In a compound light microscope the lens closest to the eye is the __________ lens.

Correct Answer: A

Rationale: The correct answer is A: ocular lens. The ocular lens is the lens closest to the eye in a compound light microscope. This lens is responsible for magnifying the image produced by the objective lens. It typically has a magnification power of 10x. The objective lens, choice B, is positioned closer to the specimen and provides the primary magnification of the image. The condenser, choice C, is located beneath the stage and helps focus light onto the specimen. The stage, choice D, is where the specimen is placed for observation. Therefore, the ocular lens is the correct choice as it is the lens closest to the eye and responsible for further magnifying the image.

Question 8 of 9

A patient with a painful ulcer had a wound culture revealing Gram-negative rods with a characteristic 'safety pin' appearance. What is the most likely causative agent?

Correct Answer: A

Rationale: The correct answer is A: Yersinia pestis. Y. pestis is a Gram-negative rod that exhibits a 'safety pin' appearance on staining due to bipolar staining. This bacterium is the causative agent of plague, which can present as painful ulcers known as buboes. Y. pestis is transmitted by fleas and can cause outbreaks in humans. Summary: - B: Francisella tularensis causes tularemia, not typically associated with painful ulcers. - C: Brucella abortus causes brucellosis, which does not typically present with painful ulcers. - D: Clostridium botulinum causes botulism, characterized by muscle weakness and paralysis, not painful ulcers.

Question 9 of 9

A Gram-positive, spore-forming bacterium was isolated from a wound infection. The bacteria were anaerobic and produced gas. What is the likely causative agent?

Correct Answer: A

Rationale: The correct answer is A: Clostridium perfringens. This bacterium is Gram-positive, spore-forming, anaerobic, and produces gas. Clostridium perfringens is commonly associated with wound infections due to its ability to produce gas gangrene. Choice B: Bacillus anthracis is also a Gram-positive, spore-forming bacterium, but it does not typically produce gas in wound infections. Choice C: Clostridium botulinum is a spore-forming, anaerobic bacterium, but it is associated with foodborne botulism rather than wound infections. Choice D: Clostridium tetani is a spore-forming, anaerobic bacterium that causes tetanus, but it does not produce gas in wound infections.

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