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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor= {{YD}} (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
Line 20: Line 21:
|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=General Principles
|SubCategory=General Principles
|Prompt=A researcher is studying the life cycle of Clostridium difficile. He allows the growth of C. difficile in appropriate culture media for several days and notes his observations during the experiment. The researcher reveals that at a specific stage during the life cycle, levels of dipicolinic acid rise significantly. Based on the diagram below, these changes most likely correspond to which phase of the C. difficile growth curve?
|Prompt=A researcher is studying the life cycle of ''Clostridium difficile''. He enriches for ''C. difficile'' in the appropriate anerobic culture media for several days and at samples the culture a several stages during the experiment. The researcher reveals that at a specific time point in the life cycle, levels of dipicolinic acid in the cell lysate rise significantly. Based on the diagram below, these changes most likely correspond to which phase of the ''C. difficile'' growth curve?


[[Image:WBR0845.png|500px]]
[[Image:WBR0845.png|500px]]
|Explanation=C. difficile are gram-positive, endospore forming, anaerobic bacilli. Spores are defined as a one-celled reproductive unit that may resist heart and chemicals and have almost no metabolic activity. Spores contain dipicolinic acid in their core. In addition to Clostridium difficile, other Clostridia species, such as C. botulinum, C. perfringens, and C. tetani and other organisms like Bacillus anthracis, Bacillus cereus, and Coxiella burnetii are all capable of forming spores.
|Explanation=''C. difficile'' are gram-positive, spore forming, anaerobic bacilli. Spores are defined as one-celled reproductive units that resist heat and chemicals and have almost no metabolic activity. Spores contain dipicolinic acid in their core. In addition to Clostridium difficile, other Clostridia species, such as C. botulinum, C. perfringens, and C. tetani and other organisms like Bacillus anthracis, Bacillus cereus, and Coxiella burnetii are all capable of forming spores. Based on the bacterial growth curve explained below, spore formation is typically seen at the end of the stationary phase of the life cycle, when nutrients become limited and survival conditions for the bacteria become harsher. It is one of the most advanced survival mechanisms and is a major health concern particularly that these spores survive a large number of chemical treatments.
 
Based on the bacterial growth curve explained below, spore formation is typically seen at the end of the stationary phase of the life cycle, where nutrients become limited and survival conditions for the bacteria become harsher.  
 
[[Bacterial_Growth_Curve.png|500px]]


Educational Objective: Spores contain dipicolinic acid in their core. They are typically formed at the end of the bacterial growth curve.
[[Image:Bacterial_Growth_Curve.png|500px]]
|AnswerA=A
|AnswerA=A
|AnswerAExp=A corresponds to the lag phase of the bacterial growth curve
|AnswerAExp=A corresponds to the lag phase of the bacterial growth curve
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|AnswerE=E
|AnswerE=E
|AnswerEExp=E corresponds to the end of the stationary phase and the beginning of the death phase due to limited resources for the bacteria to survive.
|AnswerEExp=E corresponds to the end of the stationary phase and the beginning of the death phase due to limited resources for the bacteria to survive.
|EducationalObjectives=Spores are typically formed at the end of the bacterial growth curve when nutrients become limited and survival conditions for the bacteria become harsher. They contain dipicolinic acid in their core.
|References=Paredes-sabja D, Bond C, Carman RJ, Setlow P, Sarker MR. Germination of spores of Clostridium difficile strains, including isolates from a hospital outbreak of Clostridium difficile-associated disease (CDAD). Microbiology (Reading, Engl). 2008;154(Pt 8):2241-50.
|RightAnswer=E
|RightAnswer=E
|WBRKeyword=bacteria, bacterial, growth, curve, stationary, lag, phase, exponential, death, stationary, spore, endospore, forming, formation, clostridium, clostridial, difficile, C. difficile, resistance, resistant, heat, chemicals
|WBRKeyword=Bacteria, Bacterial growth curve, Stationary phase, Lag phase, Exponential death, Stationary phase, Spore, Spore-forming, Endospore, Clostridium difficile, Clostridium, Resistance,
|Approved=No
|Approved=Yes
}}
}}

Latest revision as of 01:51, 28 October 2020
Author [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Serge Korjian)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Microbiology
Sub Category SubCategory::General Principles
Prompt [[Prompt::A researcher is studying the life cycle of Clostridium difficile. He enriches for C. difficile in the appropriate anerobic culture media for several days and at samples the culture a several stages during the experiment. The researcher reveals that at a specific time point in the life cycle, levels of dipicolinic acid in the cell lysate rise significantly. Based on the diagram below, these changes most likely correspond to which phase of the C. difficile growth curve?

]]

Answer A AnswerA::A
Answer A Explanation AnswerAExp::A corresponds to the lag phase of the bacterial growth curve
Answer B AnswerB::B
Answer B Explanation AnswerBExp::B corresponds to the beginning of the exponential phase of the bacterial growth curve.
Answer C AnswerC::C
Answer C Explanation AnswerCExp::C corresponds to the exponential phase of the bacterial growth curve.
Answer D AnswerD::D
Answer D Explanation AnswerDExp::D corresponds to the beginning of the stationary phase of the bacterial growth curve.
Answer E AnswerE::E
Answer E Explanation AnswerEExp::E corresponds to the end of the stationary phase and the beginning of the death phase due to limited resources for the bacteria to survive.
Right Answer RightAnswer::E
Explanation [[Explanation::C. difficile are gram-positive, spore forming, anaerobic bacilli. Spores are defined as one-celled reproductive units that resist heat and chemicals and have almost no metabolic activity. Spores contain dipicolinic acid in their core. In addition to Clostridium difficile, other Clostridia species, such as C. botulinum, C. perfringens, and C. tetani and other organisms like Bacillus anthracis, Bacillus cereus, and Coxiella burnetii are all capable of forming spores. Based on the bacterial growth curve explained below, spore formation is typically seen at the end of the stationary phase of the life cycle, when nutrients become limited and survival conditions for the bacteria become harsher. It is one of the most advanced survival mechanisms and is a major health concern particularly that these spores survive a large number of chemical treatments.


Educational Objective: Spores are typically formed at the end of the bacterial growth curve when nutrients become limited and survival conditions for the bacteria become harsher. They contain dipicolinic acid in their core.
References: Paredes-sabja D, Bond C, Carman RJ, Setlow P, Sarker MR. Germination of spores of Clostridium difficile strains, including isolates from a hospital outbreak of Clostridium difficile-associated disease (CDAD). Microbiology (Reading, Engl). 2008;154(Pt 8):2241-50.]]

Approved Approved::Yes
Keyword WBRKeyword::Bacteria, WBRKeyword::Bacterial growth curve, WBRKeyword::Stationary phase, WBRKeyword::Lag phase, WBRKeyword::Exponential death, WBRKeyword::Stationary phase, WBRKeyword::Spore, WBRKeyword::Spore-forming, WBRKeyword::Endospore, WBRKeyword::Clostridium difficile, WBRKeyword::Clostridium, WBRKeyword::Resistance
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