View source for WBR0344

{{WBRQuestion
|QuestionAuthor={{SSK}} {{Alison}} (Reviewed by Serge Korjian)
|ExamType=USMLE Step 1
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|SubCategory=General Principles
|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=General Principles
|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 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''.

|AnswerA=''Legionella pneumophila''
|AnswerAExp=''Legionella pneumophila'' is an obligate aerobe.
|AnswerB=''Pseudomonas aeruginosa''
|AnswerBExp=''Pseudomonas aeruginosa'' is an obligate aerobe.
|AnswerC=''Bacteroides fragilis''
|AnswerCExp=''Bacteroides fragilis'' is an obligate anaerobe.
|AnswerD=''Actinomyces israelii''
|AnswerDExp=''Actinomyces israelii'' is an obligate anaerobe.
|AnswerE=''Escherichia coli''
|AnswerEExp=''Escherichia coli'' is facultatively anaerobic.
|EducationalObjectives=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/
|RightAnswer=E
|WBRKeyword=Faculatitive anaerobes, Obligate anaerobes, Obligate aerobes, Escherichia coli,
|Approved=Yes
}}