ATI RN
microbiology chapter 14 test bank Questions
Question 1 of 9
Agents associated with human disease but generally not a serious health risk are classified in which of the following risk groups?
Correct Answer: B
Rationale: The correct answer is B: RG2. RG2 is appropriate for agents associated with human disease that pose a moderate health risk. These agents may cause disease of varying severity, but generally do not result in serious health consequences. Other choices are incorrect because: A: RG1 is for agents not associated with disease in healthy adults, C: RG3 is for agents associated with serious or lethal human disease, and D: RG4 is for agents that pose a high risk of life-threatening disease and for which there are no treatments.
Question 2 of 9
A smear of a patient's sputum suspected for tuberculosis was prepared and stained. The smear showed red bacilli against a blue background. What staining method was used?
Correct Answer: A
Rationale: The correct answer is A: Ziehl-Neelsen staining method. This method is used to detect acid-fast bacteria like Mycobacterium tuberculosis. Step-by-step rationale: 1. Acid-fast bacteria resist decolorization with acid-alcohol. 2. The red bacilli seen in the smear indicate acid-fast bacteria. 3. Ziehl-Neelsen stain uses carbol fuchsin to stain acid-fast bacteria red. 4. The blue background is likely the counterstain methylene blue. Incorrect choices: B: Gram stain is for categorizing bacteria into Gram-positive or Gram-negative, not specific for acid-fast bacteria. C: Giemsa stain is used for blood films and detecting parasites, not acid-fast bacteria. D: Neisser stain is not a standard microbiological staining method.
Question 3 of 9
A duodenal content smear of a patient with indigestion contains protozoa 10-18 mcm large. They have piriform bodies, 4 pairs of filaments, two symmetrically located nuclei in the broadened part of body. What kind of the lowest organisms is it?
Correct Answer: A
Rationale: The correct answer is A: Lamblia. The description matches the characteristics of Giardia lamblia - a protozoan parasite that causes giardiasis. The piriform bodies, 4 pairs of filaments, and two symmetrically located nuclei are specific to Giardia lamblia. It is important to differentiate it from the other choices. Dysentery ameba (choice B) typically has a single nucleus and lacks the specific characteristics described. Trichomonas (choice C) is a flagellated protozoan with different morphology and does not match the given description. Intestinal ameba (choice D) such as Entamoeba histolytica usually has a single nucleus and different body shape compared to the described organism.
Question 4 of 9
A patient underwent esophagogastroduodenoscopy. Analysis of the biopsy material enabled doctors to diagnose him with helicobacteriosis. What property of the bacteria found in this patient had to be obligatory taken into account during their cultivation?
Correct Answer: A
Rationale: Step-by-step rationale for why choice A is correct: 1. Helicobacter pylori, the bacteria causing helicobacteriosis, is microaerophilic, requiring low oxygen levels. 2. Cultivation conditions must mimic the natural environment of the bacteria. 3. Failure to provide a microaerophilic environment can hinder bacterial growth. 4. Thus, the ability to cultivate these bacteria requires consideration of their microaerophilic nature. Summary: - Choice A is correct because Helicobacter pylori is a microaerophilic bacteria. - Choice B (Presence of urease) is incorrect as it is a characteristic used for diagnosis, not cultivation. - Choice C (Absence of spores and capsules) is incorrect as it does not relate to cultivation requirements. - Choice D (Colonization of gastral cells) is incorrect as it pertains to bacterial behavior, not cultivation needs.
Question 5 of 9
An adult patient with type 2 diabetes attends the emergency room. He reported that two days ago he was accidentally injured in the left leg, but he did not seek medical care. At the time of examination, an infected wound was found, surrounded by a large area of inflammation with characteristic tissue crepitation on palpation and with foul odor. Blood (for hemoculture) and wound secretions were taken for microbiological testing. The microscopic examination reveals large Gram-positive bacteria, with centrally located spores. These bacteria were unable to grow in vitro at presence of oxygen. The most likely cause of this disease is:
Correct Answer: B
Rationale: The correct answer is B: Clostridium perfringens. In this case, the patient's presentation of infected wound with tissue crepitation, foul odor, and Gram-positive bacteria with centrally located spores that cannot grow in the presence of oxygen is indicative of gas gangrene caused by Clostridium perfringens. This anaerobic bacterium produces various toxins that lead to tissue destruction and gas production in the affected area. Clostridium tetani (choice A) causes tetanus, characterized by muscle stiffness and spasms. Clostridium botulinum (choice C) causes botulism, leading to muscle paralysis. Clostridium difficile (choice D) is associated with antibiotic-associated diarrhea. These choices are incorrect as they do not match the clinical presentation described in the question.
Question 6 of 9
Virulence
Correct Answer: D
Rationale: The correct answer is D because virulence refers to the degree of pathogenicity of a microorganism, which can vary and is not a constant characteristic. It can be measured using LD50, which is the lethal dose that kills 50% of the test population. Therefore, all the statements in options A, B, and C are true and collectively provide a comprehensive understanding of virulence.
Question 7 of 9
Which of the following statements is accurate in explaining why gram-negative bacteria are generally more resistant to penicillin than gram-positive bacteria
Correct Answer: C
Rationale: The correct answer is C: gram-negative bacteria have an outer membrane that acts as an extra barrier. This outer membrane in gram-negative bacteria contains lipopolysaccharides and porins, which restrict the entry of antibiotics like penicillin. The outer membrane acts as an additional layer of protection, making it harder for penicillin to penetrate and reach its target, the peptidoglycan layer. Choices A, B, and D do not directly address the specific mechanism of resistance seen in gram-negative bacteria. Choice A focuses on transpeptidase enzyme quantity, which is not the primary reason for penicillin resistance. Choice B refers to β-lactamase enzymes in the periplasmic space, which are actually enzymes that degrade penicillin and contribute to resistance, but this is not unique to gram-negative bacteria. Choice D mentions a thicker cell wall, which is a characteristic of gram-positive bacteria, not gram-negative bacteria.
Question 8 of 9
Bacterial ribosomes consist mainly of:
Correct Answer: D
Rationale: The correct answer is D: rRNA. Bacterial ribosomes consist mainly of ribosomal RNA (rRNA), which plays a crucial role in protein synthesis. Ribosomes are composed of rRNA and proteins, with rRNA being the major component. rRNA serves as the structural and catalytic component of the ribosome, aiding in the binding of mRNA and tRNA during translation. Carbohydrates (A) and lipids (B) are not primary components of ribosomes, and DNA (C) is not found in ribosomes as they are involved in storing genetic information, not in protein synthesis.
Question 9 of 9
After continuous treatment with antibiotics a patient got symptoms of stomatitis. Examination of specimens of oral mucous membrane revealed some oval polymorphous Gram-positive microorganisms arranged in clusters. What microorganism may be the cause of such manifestations?
Correct Answer: C
Rationale: The correct answer is C: S.aureus. Stomatitis is commonly caused by S.aureus due to its ability to form clusters of oval polymorphous Gram-positive microorganisms. S.aureus is known to colonize the oral mucous membrane and can cause infections, especially after prolonged antibiotic use. Explanation for other choices: A: С.albicans - Candida albicans is a fungus commonly associated with oral thrush, not typically causing stomatitis. B: C.perfringens - Clostridium perfringens is a bacterium associated with food poisoning and gas gangrene, not commonly causing stomatitis. D: S.pyogenes - Streptococcus pyogenes is known to cause strep throat and skin infections, but not typically associated with stomatitis.