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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor= {{SSK}} {{Alison}} (Reviewed by Serge Korjian)
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Microbiology
|MainCategory=Microbiology
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|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=General Principles
|SubCategory=General Principles
|MainCategory=Microbiology
|MainCategory=Microbiology
|MainCategory=Microbiology
|MainCategory=Microbiology
|MainCategory=Microbiology
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|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=General Principles
|SubCategory=General Principles
|Prompt=A student is conducting an experiment to test optimal bacterial survival environments. In one set-up, he plates a mixture of bacterial organisms on blood agar and allows them to grow for several days in an incubator at 37C with ample oxygen. He then places the plate in an airtight container with an alkaline solution containing pyrogallic acid that absorbs any oxygen from the container and allows the plate to stand for several days. Which of the following organisms is likely to survive both steps?
|Prompt=A student is conducting an experiment to test optimal bacterial survival environments. She begins by plating a mixture of bacterial organisms on blood agar and allowing them to grow for several days in an incubator at 37 °C with ample oxygen. She then places the plate in an airtight container with an alkaline solution containing pyrogallic acid, which absorbs any oxygen from the container, and allows the plate to stand for several days. Which of the following organisms is most likely to survive both steps?
|Explanation=Facultatively anaerobic organisms are capable of surviving regardless of the presence of oxygen. The produce energy by aerobic respiration in the presence of oxygen, but are capable of using fermentation as a source of energy production when oxygen is not available. Examples include Staphylococcus spp. and E. coli. Escherichia coli is a gram-negative, facultative anaerobic rod-shaped organism that can produce energy using a variety of substrates. In anaerobic conditions, it uses mixed-acid fermentation producing ethanol, lactate, acetate, succinate, and carbon dioxide.
|Explanation=Facultatively anaerobic organisms are capable of surviving independent of the presence or absence of oxygen. They produce energy by aerobic respiration in the presence of oxygen, but are capable of using fermentation as a source of energy production in anaerobic situations. Examples of facultatively anaerobic organisms include ''Staphylococcus spp.'' and ''Escherichia coli''. ''E. coli'' is a gram-negative, facultative anaerobic rod-shaped organism that can produce energy using a variety of substrates. In anaerobic conditions, it uses mixed-acid fermentation producing ethanol, lactate, acetate, succinate, and carbon dioxide.
 
'''Obligate aerobes''' that depend on oxygen for energy production include: Nocardia, Pseudomonas aeruginosa, Mycobacterium tuberculosis, and Bacillus.
 
'''Obligate anaerobes''' that cannot tolerate oxygen due to oxidative damage include: Actinomyces, Bacteroides, Clostridium.
 


Educational objective: Facultatively anaerobic organisms such as E. coli can survive regardless of the presence of oxygen.
* Obligate aerobes that depend on oxygen for energy production include: ''Nocardia'', ''Pseudomonas aeruginosa'', ''Legionella spp.'', and ''Mycobacterium tuberculosis''.


* Obligate anaerobes that cannot tolerate oxygen as a result of oxidative damage include: ''Actinomyces'', Bacteroides'', and ''Clostridium''.


Reference:<br>
|AnswerA=''Legionella pneumophila''
Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Section 1, Bacteriology. Available from: http://www.ncbi.nlm.nih.gov/books/NBK7994/
|AnswerAExp=''Legionella pneumophila'' is an obligate aerobe.
|AnswerA=Bacillus cereus
|AnswerB=''Pseudomonas aeruginosa''
|AnswerAExp=Bacillus spp. are obligate aerobes.
|AnswerBExp=''Pseudomonas aeruginosa'' is an obligate aerobe.
|AnswerB=Nocardia spp.
|AnswerC=''Bacteroides fragilis''
|AnswerBExp=Nocardia spp. are obligate aerobes.
|AnswerCExp=''Bacteroides fragilis'' is an obligate anaerobe.
|AnswerC=Bacteroides fragilis
|AnswerD=''Actinomyces israelii''
|AnswerCExp=Bacteroides fragilis is an obligate anaerobe.
|AnswerDExp=''Actinomyces israelii'' is an obligate anaerobe.
|AnswerD=Actinomyces spp.
|AnswerE=''Escherichia coli''
|AnswerDExp=Actinomyces spp. are obligate anaerobes.
|AnswerEExp=''Escherichia coli'' is facultatively anaerobic.
|AnswerE=Escherichia coli
|EducationalObjectives=Facultatively anaerobic organisms such as ''Escherichia coli'' and 'Staphylococcus spp.'' can survive independent of the presence or absence of oxygen.
|AnswerEExp=Escherichia coli is the only organism among the presented to be facultatively anaerobic and can survive in conditions that lack oxygen.
|References=Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Section 1, Bacteriology. Available from: http://www.ncbi.nlm.nih.gov/books/NBK7994/
|RightAnswer=E
|RightAnswer=E
|WBRKeyword=Faculatitive anaerobes, obligate anaerobes, obligate aerobes, Escherichia coli,  
|WBRKeyword=Faculatitive anaerobes, Obligate anaerobes, Obligate aerobes, Escherichia coli,
|Approved=No
|Approved=Yes
}}
}}

Latest revision as of 00:14, 28 October 2020

 
Author [[PageAuthor::Serge Korjian M.D. (Reviewed by Alison Leibowitz) (Reviewed by Serge Korjian)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Microbiology
Sub Category SubCategory::General Principles
Prompt [[Prompt::A student is conducting an experiment to test optimal bacterial survival environments. She begins by plating a mixture of bacterial organisms on blood agar and allowing them to grow for several days in an incubator at 37 °C with ample oxygen. She then places the plate in an airtight container with an alkaline solution containing pyrogallic acid, which absorbs any oxygen from the container, and allows the plate to stand for several days. Which of the following organisms is most likely to survive both steps?]]
Answer A AnswerA::''Legionella pneumophila''
Answer A Explanation AnswerAExp::''Legionella pneumophila'' is an obligate aerobe.
Answer B AnswerB::''Pseudomonas aeruginosa''
Answer B Explanation AnswerBExp::''Pseudomonas aeruginosa'' is an obligate aerobe.
Answer C AnswerC::''Bacteroides fragilis''
Answer C Explanation AnswerCExp::''Bacteroides fragilis'' is an obligate anaerobe.
Answer D AnswerD::''Actinomyces israelii''
Answer D Explanation AnswerDExp::''Actinomyces israelii'' is an obligate anaerobe.
Answer E AnswerE::''Escherichia coli''
Answer E Explanation AnswerEExp::''Escherichia coli'' is facultatively anaerobic.
Right Answer RightAnswer::E
Explanation [[Explanation::Facultatively anaerobic organisms are capable of surviving independent of the presence or absence of oxygen. They produce energy by aerobic respiration in the presence of oxygen, but are capable of using fermentation as a source of energy production in anaerobic situations. Examples of facultatively anaerobic organisms include Staphylococcus spp. and Escherichia coli. E. coli is a gram-negative, facultative anaerobic rod-shaped organism that can produce energy using a variety of substrates. In anaerobic conditions, it uses mixed-acid fermentation producing ethanol, lactate, acetate, succinate, and carbon dioxide.
  • Obligate aerobes that depend on oxygen for energy production include: Nocardia, Pseudomonas aeruginosa, Legionella spp., and Mycobacterium tuberculosis.
  • Obligate anaerobes that cannot tolerate oxygen as a result of oxidative damage include: Actinomyces, Bacteroides, and Clostridium.

Educational Objective: Facultatively anaerobic organisms such as Escherichia coli and 'Staphylococcus spp. can survive independent of the presence or absence of oxygen.
References: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Section 1, Bacteriology. Available from: http://www.ncbi.nlm.nih.gov/books/NBK7994/]]

Approved Approved::Yes
Keyword WBRKeyword::Faculatitive anaerobes, WBRKeyword::Obligate anaerobes, WBRKeyword::Obligate aerobes, WBRKeyword::Escherichia coli
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