WBR0053
| Author | [[PageAuthor::William J Gibson (Reviewed by Rim Halaby, M.D. [1])]] |
|---|---|
| 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. Which of the following organisms will he be unable to visualize with this method? |
| Answer A | AnswerA::Streptococcus pyogenes |
| Answer A Explanation | [[AnswerAExp::Streptococcus pyogenes is a gram positive coccus.]] |
| Answer B | AnswerB::Haemophilus influenzae |
| Answer B Explanation | [[AnswerBExp::Haemophilus influenzae is a gram negative rod.]] |
| Answer C | AnswerC::Bacteriodes fragilis |
| Answer C Explanation | [[AnswerCExp::Bacteriodes fragilis is a gram negative rod.]] |
| Answer D | AnswerD::Legionella pneumophila |
| 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::Corynebacterium diptheria |
| Answer E Explanation | [[AnswerEExp::Corynebacterium diptheria is a gram positive rod.]] |
| 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. Legionella infection can cause the very severe Legionnaire's 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. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Bacteria, WBRKeyword::Microbiology, WBRKeyword::Legionella, WBRKeyword::Gram stain, WBRKeyword::Stain |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |