WBR0845

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 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? ]]
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, 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. 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. Educational Objective: Spores contain dipicolinic acid in their core. They are typically formed at the end of the bacterial growth curve. References: ]]
Approved	Approved::Yes
Keyword	WBRKeyword::bacteria, WBRKeyword::bacterial, WBRKeyword::growth, WBRKeyword::curve, WBRKeyword::stationary, WBRKeyword::lag, WBRKeyword::phase, WBRKeyword::exponential, WBRKeyword::death, WBRKeyword::stationary, WBRKeyword::spore, WBRKeyword::endospore, WBRKeyword::forming, WBRKeyword::formation, WBRKeyword::clostridium, WBRKeyword::clostridial, WBRKeyword::difficile, WBRKeyword::C. difficile, WBRKeyword::resistance, WBRKeyword::resistant, WBRKeyword::heat, WBRKeyword::chemicals
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