A 16 y.o. boy from a countryside entered an educational establishment. Scheduled Manteux test revealed that the boy had negative reaction. What are the most reasonable actions in this case?

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Microbiology An Introduction 13th Edition Test Bank Questions

Question 1 of 9

A 16 y.o. boy from a countryside entered an educational establishment. Scheduled Manteux test revealed that the boy had negative reaction. What are the most reasonable actions in this case?

Correct Answer: C

Rationale: The correct answer is C: To perform serodiagnostics of tuberculosis. Rationale: The negative reaction to the Mantoux test indicates absence of TB infection. Performing serodiagnostics will further confirm the absence of active infection. This is important to rule out TB before considering vaccination or isolation measures. Summary: A: BCG vaccination is not necessary as the boy shows a negative reaction to the Mantoux test. B: Repeating the test in a month is unnecessary as the initial test already showed a negative reaction. D: Isolating the boy is not warranted as there is no evidence of active TB infection.

Question 2 of 9

The main factor in pathogenicity of diphtheria is:

Correct Answer: C

Rationale: The correct answer is C because the main factor in the pathogenicity of diphtheria is the exotoxin produced by the bacterium Corynebacterium diphtheriae. This exotoxin inhibits protein synthesis in host cells, leading to tissue damage and the characteristic symptoms of diphtheria. A: The metachromatic bodies of Ernst-Babes are not the main factor in diphtheria pathogenicity. B: While endotoxins can contribute to the pathogenicity of some bacteria, in diphtheria, the main factor is the exotoxin. D: This is incorrect as the main factor in diphtheria pathogenicity is the exotoxin.

Question 3 of 9

A patient with fever and chills had blood cultures revealing Gram-negative rods that were oxidase-positive and lactose non-fermenters. What is the most likely causative agent?

Correct Answer: A

Rationale: The correct answer is A: Pseudomonas aeruginosa. This is because Pseudomonas is a Gram-negative rod, oxidase-positive, and a lactose non-fermenter. The presence of fever and chills suggests a systemic infection, which is common with Pseudomonas. Salmonella typhi, Shigella dysenteriae, and Escherimalia coli are all Gram-negative rods but are typically lactose fermenters and do not match the characteristics described in the question.

Question 4 of 9

A 70-year-old man was admitted to the hospital after suffering extensive third-degree burns. Three days later he spiked a fever and there was pus on the dressing that had blue-green colour. Gram stain of the pus revealed gram-negative rods. The most possible cause of these findings is:

Correct Answer: A

Rationale: The correct answer is A: The pyocyanin released by Pseudomonas aeruginosa. Pyocyanin is a blue-green pigment produced by Pseudomonas aeruginosa, a common cause of nosocomial infections in burn patients. The presence of blue-green pus and gram-negative rods in the wound along with fever suggests an infection with Pseudomonas aeruginosa. The other choices are incorrect because E. Coli typically causes gastrointestinal infections and releases enterotoxins, Staphylococcus aureus releases hemolysins causing hemolysis of red blood cells, and Shigella dysenteriae releases shigatoxin causing bloody diarrhea, none of which match the clinical presentation described in the question.

Question 5 of 9

The decrease in blood clotting by heparin occurs at which general site of action?

Correct Answer: B

Rationale: The correct answer is B: Extracellular. Heparin works by inhibiting clotting factors in the blood outside of cells, preventing the formation of blood clots. It does not directly affect cellular, neuromuscular, or intracellular processes. By targeting extracellular factors, heparin effectively reduces the ability of blood to clot, making it an effective anticoagulant. The other choices are incorrect because heparin does not act on cellular, neuromuscular, or intracellular sites in the body to decrease blood clotting.

Question 6 of 9

A wound culture grew Gram-positive rods with central spores. The bacteria were catalase-positive and aerobic. Identify the microorganism.

Correct Answer: A

Rationale: The correct answer is A: Bacillus anthracis. The presence of Gram-positive rods with central spores, catalase-positive, and aerobic growth characteristics are indicative of Bacillus anthracis. Bacillus anthracis is known for its central spores and ability to grow aerobically. Summary of why other choices are incorrect: B: Clostridium tetani is a Gram-positive rod with terminal spores and is anaerobic. C: Streptococcus pyogenes is a Gram-positive cocci and catalase-negative. D: Klebsiella pneumoniae is a Gram-negative rod and catalase-positive, but is not associated with central spores.

Question 7 of 9

Microorganisms that show optimal growth in moderate temperatures (between 25° C and 40° C) are called:

Correct Answer: C

Rationale: The correct answer is C: mesophiles. Mesophiles are microorganisms that thrive in moderate temperatures, typically between 25°C and 40°C. This temperature range is ideal for their growth and reproduction. Thermophiles (A) prefer high temperatures, psychrophiles (B) thrive in cold temperatures, and psychrotrophs (D) can grow at refrigeration temperatures but have an optimal range above 20°C. Therefore, the mesophiles are the best fit for organisms that show optimal growth in moderate temperatures.

Question 8 of 9

A patient suffering from syphilis was prescribed a drug the action of which based upon disturbed generation of murein leading to death of the causative agent. What drug is it?

Correct Answer: A

Rationale: The correct answer is A: Benzylpenicillin sodium salt. Benzylpenicillin is a beta-lactam antibiotic that inhibits the synthesis of bacterial cell walls by disrupting the formation of murein (peptidoglycan), leading to bacterial cell death. This mechanism specifically targets the causative agent of syphilis, Treponema pallidum. - Choice B: Bijochinol is not a known drug used to treat syphilis. - Choice C: Ciprofloxacin is a fluoroquinolone antibiotic that works by inhibiting bacterial DNA replication and is not the first-line treatment for syphilis. - Choice D: Azithromycin is a macrolide antibiotic that interferes with bacterial protein synthesis and is commonly used to treat other infections but is not the preferred treatment for syphilis.

Question 9 of 9

The normal flora present in the healthy male reproductive system is best characterized as:

Correct Answer: C

Rationale: Rationale: 1. The male reproductive system is considered sterile as it does not have a natural microbiota. 2. Any presence of microorganisms in this system could indicate an infection or disease. 3. Therefore, choice C, sterile with no normal flora, is the best characterization. Summary: A: Incorrect - The male reproductive system does not typically have gram-positive rods. B: Incorrect - Acid-fast rods are not part of the normal flora in the male reproductive system. D: Incorrect - The male reproductive system does not typically have gram-positive spore formers.

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