A 24-year-old man presents with low-grade fever and shortness of breath for the last 3 weeks. Past medical history is significant for severe mitral regurgitation status post mitral valve replacement five years ago. His temperature is 38.3°C (101.0°F) and respiratory rate is 18/min. Physical examination reveals vertical hemorrhages under his nails, multiple painless erythematous lesions on his palms, and two tender, raised nodules on his fingers. Cardiac auscultation reveals a new-onset 2/6 holosystolic murmur loudest at the apex with the patient in the left lateral decubitus position. A transesophageal echocardiogram reveals vegetations on the prosthetic valve. Blood cultures reveal catalase-positive, gram-positive cocci. Which of the following characteristics is associated with the organism most likely responsible for this patient’s condition?
Q72
Blood cultures are sent to the laboratory. Intravenous antibiotic therapy is started. Transesophageal echocardiography shows a large, oscillating vegetation attached to the tricuspid valve. There are multiple small vegetations attached to tips of the tricuspid valve leaflets. There is moderate tricuspid regurgitation. The left side of the heart and the ejection fraction are normal. Which of the following is the most likely causal organism of this patient's condition?
Q73
A 47-year-old woman comes to the physician because of a 6-week history of fatigue and low-grade fever. She has no history of serious illness except for a bicuspid aortic valve, diagnosed 10 years ago. She does not use illicit drugs. Her temperature is 37.7°C (99.9°F). Physical examination shows petechiae under the fingernails and multiple tender, red nodules on the fingers. A new grade 2/6 diastolic murmur is heard at the right second intercostal space. Which of the following is the most likely causal organism?
Q74
A 74-year-old female is brought to the emergency department because of a 2-week history of increasing weakness and chills. She also notes difficulty breathing for the last three days. Eight weeks ago, she underwent left hemicolectomy for adenocarcinoma of the colon. She subsequently developed a severe urinary tract infection, was treated in the intensive care unit for four days, and was discharged from the hospital three weeks ago. She has type 2 diabetes mellitus, osteoporosis with lumbar pain, hypertension, and atrial fibrillation. She has smoked one pack of cigarettes daily for 50 years. She does not drink alcohol and has never used illicit drugs. Current medications include warfarin, metformin, lisinopril, and aspirin. She appears lethargic and has a large conjunctival hemorrhage in her left eye. Her temperature is 39.3°C (102.7°F), pulse is 112/min, respirations are 25/min, and blood pressure is 126/79 mm Hg. Cardiac auscultation reveals a new holosystolic murmur over the apex. Abdominal examination shows mild, diffuse tenderness throughout the upper quadrants and a well-healed 12-cm paramedian scar. There are multiple tender nodules on the palmar surface of her fingertips. Funduscopic examination shows retinal hemorrhages with pale centers. An ECG shows atrial fibrillation and right bundle branch block. Which of the following is the most likely underlying etiology of this patient's condition?
Q75
A 43-year-old woman presents to the emergency department complaining of palpitations, dry cough, and shortness of breath for 1 week. She immigrated to the United States from Korea at the age of 20. She says that her heart is racing and she has never felt these symptoms before. Her cough is dry and is associated with shortness of breath that occurs with minimal exertion. Her past medical history is otherwise unremarkable. She has no allergies and is not currently taking any medications. She is a nonsmoker and an occasional drinker. She denies illicit drug use. Her blood pressure is 100/65 mm Hg, pulse is 76/min, respiratory rate is 23/min, and temperature is 36.8°C (98.2°F). Her physical examination is significant for bibasilar lung crackles and a non-radiating, low-pitched, mid-diastolic rumbling murmur best heard at the apical region. In addition, she has jugular vein distention and bilateral pitting edema in her lower extremities. Which of the following best describes the infectious agent that led to this patient’s condition?
Gram-positive US Medical PG Practice Questions and MCQs
Question 71: A 24-year-old man presents with low-grade fever and shortness of breath for the last 3 weeks. Past medical history is significant for severe mitral regurgitation status post mitral valve replacement five years ago. His temperature is 38.3°C (101.0°F) and respiratory rate is 18/min. Physical examination reveals vertical hemorrhages under his nails, multiple painless erythematous lesions on his palms, and two tender, raised nodules on his fingers. Cardiac auscultation reveals a new-onset 2/6 holosystolic murmur loudest at the apex with the patient in the left lateral decubitus position. A transesophageal echocardiogram reveals vegetations on the prosthetic valve. Blood cultures reveal catalase-positive, gram-positive cocci. Which of the following characteristics is associated with the organism most likely responsible for this patient’s condition?
A. Coagulase positive
B. DNAse positive
C. Hemolysis
D. Novobiocin sensitive (Correct Answer)
E. Optochin sensitive
Explanation: ***Novobiocin sensitive***
- The patient has **prosthetic valve endocarditis** caused by a **catalase-positive, gram-positive coccus**, which is most likely **_Staphylococcus epidermidis_** due to its association with foreign bodies and prosthetic devices.
- _Staphylococcus epidermidis_ is a **coagulase-negative staphylococcus** that is **novobiocin sensitive**, helping to differentiate it from other coagulase-negative staphylococci like **_Staphylococcus saprophyticus_** (novobiocin resistant).
- Although this is late prosthetic valve endocarditis (5 years post-surgery), _S. epidermidis_ remains a common pathogen due to biofilm formation on prosthetic materials.
*Coagulase positive*
- **Coagulase-positive** gram-positive cocci, such as **_Staphylococcus aureus_**, are a common cause of endocarditis, especially in intravenous drug users and can also cause prosthetic valve endocarditis.
- However, the correct answer requires identifying the characteristic that differentiates the most likely organism, and **coagulase-negative** staphylococci like _S. epidermidis_ are more characteristically associated with prosthetic device infections due to their biofilm-forming capabilities.
- A positive coagulase test differentiates _S. aureus_ from coagulase-negative staphylococci.
*DNAse positive*
- **DNAse positivity** is characteristic of **_Staphylococcus aureus_** and group A beta-hemolytic streptococci (_Streptococcus pyogenes_).
- While _S. aureus_ can cause prosthetic valve endocarditis, the question asks for the characteristic most associated with the likely organism, which in the context of prosthetic devices is typically **_S. epidermidis_** (DNAse negative).
*Hemolysis*
- **Hemolysis patterns** are primarily used to differentiate **streptococcal species**, not staphylococci. For example, **beta-hemolytic streptococci** cause complete hemolysis.
- While some staphylococci can show hemolytic activity, it is not a primary characteristic used to differentiate between the most likely staphylococcal causes of prosthetic valve endocarditis.
*Optochin sensitive*
- **Optochin sensitivity** is a key characteristic used to identify **_Streptococcus pneumoniae_**.
- _S. pneumoniae_ is **catalase-negative**, while the described organism is **catalase-positive**, ruling out _S. pneumoniae_ as the causative agent.
Question 72: Blood cultures are sent to the laboratory. Intravenous antibiotic therapy is started. Transesophageal echocardiography shows a large, oscillating vegetation attached to the tricuspid valve. There are multiple small vegetations attached to tips of the tricuspid valve leaflets. There is moderate tricuspid regurgitation. The left side of the heart and the ejection fraction are normal. Which of the following is the most likely causal organism of this patient's condition?
A. Streptococcus sanguinis
B. Staphylococcus aureus (Correct Answer)
C. Enterococcus faecalis
D. Neisseria gonorrhoeae
E. Staphylococcus epidermidis
Explanation: ***Staphylococcus aureus***
- **_Staphylococcus aureus_** is the most common cause of **acute infective endocarditis**, particularly in intravenous drug users, which often affects the **tricuspid valve**.
- The presence of large, oscillating vegetations and **multiple small vegetations** on the tricuspid valve strongly suggests an aggressive infection, typical of _S. aureus_.
*Streptococcus sanguinis*
- _Streptococcus sanguinis_ is a common cause of **subacute infective endocarditis** in patients with pre-existing valvular disease but rarely causes acute, aggressive right-sided endocarditis.
- It's typically associated with **dental procedures** and usually affects the left side of the heart.
*Enterococcus faecalis*
- _Enterococcus faecalis_ can cause endocarditis, often associated with **genitourinary or gastrointestinal procedures**, and typically affects older men.
- While it can cause virulent endocarditis, it is less commonly associated with acute right-sided disease in this demographic compared to _S. aureus_.
*Neisseria gonorrhoeae*
- **_Neisseria gonorrhoeae_** is a rare cause of endocarditis, usually seen in younger, sexually active individuals, and often involves the aortic valve.
- While it can be acute, it is an extremely uncommon cause of **tricuspid valve endocarditis**.
*Staphylococcus epidermidis*
- **_Staphylococcus epidermidis_** is primarily associated with **prosthetic valve endocarditis** or foreign bodies, often presenting as a subacute infection.
- It rarely causes natural valve endocarditis, especially acute right-sided disease in this context.
Question 73: A 47-year-old woman comes to the physician because of a 6-week history of fatigue and low-grade fever. She has no history of serious illness except for a bicuspid aortic valve, diagnosed 10 years ago. She does not use illicit drugs. Her temperature is 37.7°C (99.9°F). Physical examination shows petechiae under the fingernails and multiple tender, red nodules on the fingers. A new grade 2/6 diastolic murmur is heard at the right second intercostal space. Which of the following is the most likely causal organism?
A. Staphylococcus epidermidis
B. Streptococcus pyogenes
C. Streptococcus sanguinis (Correct Answer)
D. Streptococcus pneumoniae
E. Enterococcus faecalis
Explanation: ***Streptococcus sanguinis***
- The patient's presentation with **fatigue, low-grade fever, petechiae, tender nodules (Osler nodes)**, and a **new diastolic murmur** in a patient with a **bicuspid aortic valve** is highly suggestive of **infective endocarditis**.
- **Streptococcus sanguinis** (and other viridans streptococci) are common causes of subacute bacterial endocarditis, often associated with **oral flora** and pre-existing valvular heart disease.
*Staphylococcus epidermidis*
- This organism is a common cause of **prosthetic valve endocarditis** and **nosocomial infections** but is less likely to cause endocarditis in a native valve without a history of recent surgery or intravenous lines.
- While it can cause endocarditis, the clinical features here, especially the lack of recent medical interventions, point away from *S. epidermidis* as the primary cause.
*Streptococcus pyogenes*
- **Streptococcus pyogenes** is primarily known for causing **strep throat, scarlet fever, and rheumatic fever**, which can lead to rheumatic heart disease but rarely causes acute or subacute infective endocarditis directly.
- It typically causes more acute and severe infections, which doesn't align with the 6-week history of low-grade fever and fatigue.
*Streptococcus pneumoniae*
- **Streptococcus pneumoniae** is a common cause of **pneumonia, meningitis, and otitis media** but is an uncommon cause of infective endocarditis, accounting for a very small percentage of cases.
- Endocarditis due to *S. pneumoniae* tends to be **acute and fulminant**, often associated with severe systemic illness, which is not fully consistent with the subacute presentation here.
*Enterococcus faecalis*
- **Enterococcus faecalis** is a common cause of **nosocomial urinary tract infections** and can cause endocarditis, especially in older patients or those with gastrointestinal or genitourinary procedures.
- While it's a possibility for endocarditis, the oral flora association with viridans streptococci (like *S. sanguinis*) in the context of a bicuspid aortic valve makes it a more direct fit.
Question 74: A 74-year-old female is brought to the emergency department because of a 2-week history of increasing weakness and chills. She also notes difficulty breathing for the last three days. Eight weeks ago, she underwent left hemicolectomy for adenocarcinoma of the colon. She subsequently developed a severe urinary tract infection, was treated in the intensive care unit for four days, and was discharged from the hospital three weeks ago. She has type 2 diabetes mellitus, osteoporosis with lumbar pain, hypertension, and atrial fibrillation. She has smoked one pack of cigarettes daily for 50 years. She does not drink alcohol and has never used illicit drugs. Current medications include warfarin, metformin, lisinopril, and aspirin. She appears lethargic and has a large conjunctival hemorrhage in her left eye. Her temperature is 39.3°C (102.7°F), pulse is 112/min, respirations are 25/min, and blood pressure is 126/79 mm Hg. Cardiac auscultation reveals a new holosystolic murmur over the apex. Abdominal examination shows mild, diffuse tenderness throughout the upper quadrants and a well-healed 12-cm paramedian scar. There are multiple tender nodules on the palmar surface of her fingertips. Funduscopic examination shows retinal hemorrhages with pale centers. An ECG shows atrial fibrillation and right bundle branch block. Which of the following is the most likely underlying etiology of this patient's condition?
A. Staphylococcus aureus infection (Correct Answer)
B. Aspergillus fumigatus infection
C. Streptococcus sanguinis infection
D. Pulmonary metastases
E. Cardiobacterium hominis infection
Explanation: ***Staphylococcus aureus infection***
- The patient presents with classic signs of **infective endocarditis** (IE), including fever, new holosystolic murmur, Roth spots (retinal hemorrhages with pale centers), and Osler's nodes (tender nodules on fingertips). The recent **urinary tract infection (UTI)** and hospitalization provide a source for bacteremia.
- **_S. aureus_** is a common cause of IE, particularly in healthcare-associated cases or following procedures, and is known for its virulence and ability to infect previously damaged or prosthetic valves. The patient's risk factors like advanced age, recent surgery, and UTI increase her susceptibility.
*Aspergillus fumigatus infection*
- **_Aspergillus_** typically causes infective endocarditis in immunocompromised patients, IV drug users, or those with prosthetic valves, often in a subacute or chronic course.
- While the patient is elderly and has comorbidities, there is no direct evidence of severe immunocompromise (e.g., neutropenia) or IV drug use, making **bacterial endocarditis** more likely given the acute presentation and classical stigmata.
*Streptococcus sanguinis infection*
- **_Streptococcus sanguinis_** is part of the **viridans group streptococci** and is a common cause of subacute IE, especially in patients with pre-existing valvular disease following dental procedures.
- The patient's recent history does not point to a clear dental source, and her recent UTI and hospitalization make a more aggressive pathogen like **_S. aureus_** a stronger consideration for her acute, severe presentation.
*Pulmonary metastases*
- While the patient has a history of **colon adenocarcinoma**, pulmonary metastases typically present with respiratory symptoms like cough and dyspnea, and sometimes hemoptysis, but do not explain the systemic signs of infection (fever, chills), signs of **infective endocarditis** (new murmur, Roth spots, Osler's nodes), or the recent UTI as a potential portal of entry for bacteremia.
- Metastases would not cause a new **holosystolic murmur** or the characteristic peripheral stigmata of endocarditis.
*Cardiobacterium hominis infection*
- **_Cardiobacterium hominis_** is a member of the **HACEK group** of bacteria, known for causing slow-growing, indolent endocarditis, often with large vegetations.
- The patient's presentation is more acute and severe, with a clear recent history of hospitalization and a UTI, which is not a typical source for **HACEK organisms**. Their involvement in IE is usually much slower in onset and progression.
Question 75: A 43-year-old woman presents to the emergency department complaining of palpitations, dry cough, and shortness of breath for 1 week. She immigrated to the United States from Korea at the age of 20. She says that her heart is racing and she has never felt these symptoms before. Her cough is dry and is associated with shortness of breath that occurs with minimal exertion. Her past medical history is otherwise unremarkable. She has no allergies and is not currently taking any medications. She is a nonsmoker and an occasional drinker. She denies illicit drug use. Her blood pressure is 100/65 mm Hg, pulse is 76/min, respiratory rate is 23/min, and temperature is 36.8°C (98.2°F). Her physical examination is significant for bibasilar lung crackles and a non-radiating, low-pitched, mid-diastolic rumbling murmur best heard at the apical region. In addition, she has jugular vein distention and bilateral pitting edema in her lower extremities. Which of the following best describes the infectious agent that led to this patient’s condition?
A. A bacterium that induces partial lysis of red cells with hydrogen peroxide
B. A bacterium that requires an anaerobic environment to grow properly
C. A bacterium that does not lyse red cells
D. A bacterium that induces heme degradation of the red cells of a blood agar plate
E. A bacterium that induces complete lysis of the red cells of a blood agar plate with an oxygen-sensitive cytotoxin (Correct Answer)
Explanation: ***A bacterium that induces complete lysis of the red cells of a blood agar plate with an oxygen-sensitive cytotoxin***
- This describes **Group A Streptococcus (GAS)**, specifically *Streptococcus pyogenes*, which causes **rheumatic fever** leading to **mitral stenosis**. Mitral stenosis is characterized by a **mid-diastolic rumbling murmur** at the apex, left atrial enlargement causing **palpitations**, and **pulmonary congestion** leading to dyspnea, cough, and bibasilar crackles.
- The delayed onset of symptoms (immigrated at 20, symptoms at 43) is typical for **rheumatic heart disease**, where repeated GAS infections in childhood/adolescence lead to valve damage that manifests years later. GAS produces **streptolysin O**, an **oxygen-labile cytotoxin** responsible for **beta-hemolysis** (complete lysis) on blood agar.
*A bacterium that induces partial lysis of red cells with hydrogen peroxide*
- This describes **alpha-hemolytic** bacteria like *Streptococcus pneumoniae* or *Viridans streptococci*, which cause **partial hemolysis** (greenish discoloration) on blood agar due to **hydrogen peroxide** production.
- While *Viridans streptococci* can cause **infective endocarditis**, the clinical picture of **rheumatic mitral stenosis** is more consistent with a history of recurrent streptococcal pharyngitis (GAS).
*A bacterium that requires an anaerobic environment to grow properly*
- This description typically refers to **anaerobic bacteria**, such as *Clostridium* or *Bacteroides* species.
- These bacteria are generally not associated with the primary cause of acute rheumatic fever or the subsequent development of chronic valvular heart disease like mitral stenosis.
*A bacterium that does not lyse red cells*
- This describes **gamma-hemolytic** (non-hemolytic) bacteria, such as *Enterococcus faecalis* or some *Staphylococcus* species.
- These organisms do not cause the characteristic hemolysis seen with the streptococci responsible for rheumatic fever.
*A bacterium that induces heme degradation of the red cells of a blood agar plate*
- This description is **too vague** and does not specifically identify the organism. While heme degradation occurs with various types of hemolysis, the key distinguishing feature of **Group A Streptococcus** is **complete lysis (beta-hemolysis)** combined with production of the **oxygen-sensitive toxin streptolysin O**.
- This option lacks the specificity needed to identify GAS as the causative agent of rheumatic fever. Both alpha- and beta-hemolytic organisms can degrade heme, but only beta-hemolytic GAS causes rheumatic heart disease.
