WBR0053

Author	[[PageAuthor::William J Gibson (Reviewed by Rim Halaby, M.D. [1] and Yazan Daaboul)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology, MainCategory::Pathology
Sub Category	SubCategory::General Principles, SubCategory::Infectious Disease
Prompt	Prompt::A microbiologist has been given a number of unknown clinical samples and is attempting to visualize the organisms by gram stain. Samples from which patient population will he be unable to visualize with this method?
Answer A	AnswerA::Sexually active college dormitory students
Answer A Explanation	[[AnswerAExp::Nisseria meningitidis is a gram-negative dipoloccus.]]
Answer B	AnswerB::Adult patients with a history of alcoholism
Answer B Explanation	[[AnswerBExp::Klebsiella pneumoniae is a gram-negative rod.]]
Answer C	AnswerC::Infants of pregnant women who were not screened during 3rd trimester
Answer C Explanation	[[AnswerCExp::Group B streptococcus is a gram-positive coccus.]]
Answer D	AnswerD::Patients with recent exposure to contaminated air conditioning systems
Answer D Explanation	[[AnswerDExp::Legionella pneumophila is a primarily intracellular organism which gram-stains poorly. The stain of choice for Legionella is a silver stain.]]
Answer E	AnswerE::Elderly patients with osteoarthritis who recently underwent a total hip replacement by prosthesis
Answer E Explanation	[[AnswerEExp::Staphyloccocus epidermidis is a gram-positive coccus.]]
Right Answer	RightAnswer::D
Explanation	[[Explanation::Legionella pneumophila is a primarily intracellular organism which gram-stains poorly. The stain of choice for Legionella is a silver stain. Legionella infections cause atypical pneumonia and are associated with aerosols from contaminated water, such as certain air conditioning systems or cruises in lakes and rivers. Legionella infection can cause the very severe Legionnaires' disease in older individuals. A more mild manifestation of Legionella infection is Pontiac fever. The treatment of choice for legionella infections is a macrolide (e.g. erythromycin). Educational Objective: Legionella pneumophila is a primarily intracellular organism which gram-stains poorly. The stain of choice for Legionella is a silver stain. References: First Aid 2014 page 121]]
Approved	Approved::Yes
Keyword	WBRKeyword::Bacteria, WBRKeyword::Microbiology, WBRKeyword::Legionella, WBRKeyword::Gram stain, WBRKeyword::Stain, WBRKeyword::silver, WBRKeyword::air condition, WBRKeyword::air conditioning
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::