Biofilms in device-related infections US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Biofilms in device-related infections. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Biofilms in device-related infections US Medical PG Question 1: A 37-year-old woman with a history of anorectal abscesses complains of pain in the perianal region. Physical examination reveals mild swelling, tenderness, and erythema of the perianal skin. She is prescribed oral ampicillin and asked to return for follow-up. Two days later, the patient presents with a high-grade fever, syncope, and increased swelling. Which of the following would be the most common mechanism of resistance leading to the failure of antibiotic therapy in this patient?
- A. Intrinsic absence of a target site for the drug
- B. Use of an altered metabolic pathway
- C. Production of beta-lactamase enzyme (Correct Answer)
- D. Altered structural target for the drug
- E. Drug efflux pump
Biofilms in device-related infections Explanation: ***Production of beta-lactamase enzyme***
- The patient's symptoms of a rapidly worsening infection despite ampicillin treatment suggest the presence of a **beta-lactamase producing organism**. Ampicillin is a **beta-lactam antibiotic** that is inactivated by these enzymes.
- Anorectal abscesses and rapidly progressing soft tissue infections are often caused by **polymicrobial flora**, including staphylococci and enterococci, many of which can produce **beta-lactamase**.
*Intrinsic absence of a target site for the drug*
- While some bacteria inherently lack the target site for certain drugs (e.g., mycoplasma lacking a cell wall, thus being resistant to beta-lactams), this is less likely to be the **most common mechanism of acquired resistance** leading to treatment failure in a typical perianal infection.
- The rapid progression and failed initial treatment point towards an **acquired mechanism of resistance** rather than an intrinsic one.
*Use of an altered metabolic pathway*
- This mechanism, such as altered **folate synthesis pathways** in resistance to trimethoprim-sulfamethoxazole, is less common as the primary mechanism for ampicillin resistance.
- Ampicillin's mechanism of action primarily targets the **bacterial cell wall**, not a metabolic pathway in the same way.
*Altered structural target for the drug*
- This involves modifications to the **penicillin-binding proteins (PBPs)**, which are the targets of beta-lactam antibiotics like ampicillin. While a valid mechanism (e.g., in MRSA), the **production of beta-lactamase** is generally a more widespread and common cause of ampicillin failure, especially in infections involving mixed flora from the perianal region.
- Given the abrupt failure of ampicillin, **beta-lactamase inactivation** is a more immediate and common cause than a rapid mutational change in PBPs.
*Drug efflux pump*
- **Efflux pumps** actively remove antibiotics from the bacterial cell, contributing to resistance against various drug classes.
- While efflux pumps can play a role, the dominant mechanism for resistance to **ampicillin** in many common perianal pathogens is the **enzymatic degradation by beta-lactamases**.
Biofilms in device-related infections US Medical PG Question 2: A 42-year-old woman with a history of multiple sclerosis and recurrent urinary tract infections comes to the emergency department because of flank pain and fever. Her temperature is 38.8°C (101.8°F). Examination shows left-sided costovertebral angle tenderness. She is admitted to the hospital and started on intravenous vancomycin. Three days later, her symptoms have not improved. Urine culture shows growth of Enterococcus faecalis. Which of the following best describes the most likely mechanism of antibiotic resistance in this patient?
- A. Increased efflux across bacterial cell membranes
- B. Production of beta-lactamase
- C. Alteration of penicillin-binding proteins
- D. Alteration of peptidoglycan synthesis (Correct Answer)
- E. Alteration of ribosomal targets
Biofilms in device-related infections Explanation: ***Alteration of peptidoglycan synthesis***
- **Vancomycin** targets the **D-Ala-D-Ala terminus** on the peptidoglycan precursor, preventing cross-linking during bacterial cell wall synthesis.
- **Vancomycin resistance in Enterococcus faecalis** occurs through acquisition of resistance genes (vanA, vanB) that encode enzymes modifying the peptidoglycan precursor from **D-Ala-D-Ala to D-Ala-D-Lac**.
- This structural change reduces vancomycin's binding affinity by approximately 1000-fold, rendering the antibiotic ineffective.
- The mechanism directly involves **alteration of the peptidoglycan synthesis pathway**, specifically the terminal amino acid residues of the pentapeptide precursor.
*Increased efflux across bacterial cell membranes*
- This mechanism involves **efflux pumps that actively transport antibiotics out of the bacterial cell**, reducing intracellular concentration.
- While efflux pumps contribute to resistance for antibiotics like **tetracyclines, fluoroquinolones, and macrolides**, this is not the primary mechanism of vancomycin resistance in Enterococcus.
*Production of beta-lactamase*
- **Beta-lactamase enzymes** hydrolyze the **beta-lactam ring** of antibiotics like **penicillins and cephalosporins**, rendering them inactive.
- **Vancomycin is a glycopeptide antibiotic, not a beta-lactam**, so its efficacy is not affected by beta-lactamase production.
*Alteration of ribosomal targets*
- This mechanism confers resistance to antibiotics that target **bacterial ribosomes** to inhibit protein synthesis, such as **macrolides, aminoglycosides, and tetracyclines**.
- **Vancomycin acts on cell wall synthesis**, not protein synthesis, so alteration of ribosomal targets is not relevant to vancomycin resistance.
*Alteration of penicillin-binding proteins*
- **Penicillin-binding proteins (PBPs)** are the targets of **beta-lactam antibiotics** (penicillins, cephalosporins, carbapenems).
- Alterations in PBPs cause resistance to beta-lactams, not to vancomycin.
- **Vancomycin does not interact with PBPs**; it binds directly to the D-Ala-D-Ala terminus of peptidoglycan precursors in the cell wall.
Biofilms in device-related infections US Medical PG Question 3: A 67-year-old woman comes to the physician because of fever, chills, myalgias, and joint pain 1 month after undergoing aortic prosthetic valve replacement due to high-grade aortic stenosis. She does not drink alcohol or use illicit drugs. Her temperature is 39.3°C (102.8°F). She appears weak and lethargic. Physical examination shows crackles at both lung bases and a grade 2/6, blowing diastolic murmur over the right sternal border. Laboratory studies show leukocytosis and an elevated erythrocyte sedimentation rate. The causal organism is most likely to have which of the following characteristics?
- A. Beta hemolytic, bacitracin-sensitive cocci
- B. Alpha hemolytic, optochin-resistant cocci
- C. Catalase-negative cocci that grows in 6.5% saline
- D. Novobiocin-sensitive, coagulase-negative cocci (Correct Answer)
- E. Alpha hemolytic, optochin-sensitive diplococci
Biofilms in device-related infections Explanation: ***Novobiocin-sensitive, coagulase-negative cocci***
- The patient's symptoms (fever, chills, new murmur) and recent **prosthetic valve replacement** strongly suggest **nosocomial infective endocarditis**.
- **Staphylococcus epidermidis** is a common cause of prosthetic valve endocarditis, and it is a **coagulase-negative Staphylococcus** that is characteristically **novobiocin-sensitive**.
*Beta hemolytic, bacitracin-sensitive cocci*
- This describes **Group A Streptococcus (Streptococcus pyogenes)**, which causes pharyngitis, cellulitis, and toxic shock syndrome, but rarely infective endocarditis, particularly 1 month post-op.
- While it can cause rheumatic fever (leading to valve damage), it is not a common cause of prosthetic valve endocarditis in this specific context.
*Alpha hemolytic, optochin-resistant cocci*
- This describes **Viridans group streptococci (e.g., Streptococcus mitis, S. sanguinis)**, which are common causes of native valve endocarditis, often following dental procedures.
- However, they are typically **alpha-hemolytic** and **optochin-resistant**, not associated with prosthetic valve infections in the immediate post-operative period.
*Catalase-negative cocci that grows in 6.5% saline*
- This describes **Enterococci (e.g., Enterococcus faecalis, Enterococcus faecium)**. They are catalase-negative and can grow in 6.5% saline.
- While enterococci can cause endocarditis, particularly in patients with genitourinary or gastrointestinal procedures, they are not the most likely cause of prosthetic valve endocarditis 1 month after surgery.
*Alpha hemolytic, optochin-sensitive diplococci*
- This describes **Streptococcus pneumoniae**, a common cause of pneumonia, meningitis, and otitis media.
- While it can cause endocarditis, it is less common for prosthetic valve endocarditis in this setting and would typically present with more prominent respiratory symptoms.
Biofilms in device-related infections US Medical PG Question 4: 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
Biofilms in device-related infections 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.
Biofilms in device-related infections US Medical PG Question 5: A 56-year-old woman comes to the emergency department because of worsening pain and swelling in her right knee for 3 days. She underwent a total knee arthroplasty of her right knee joint 5 months ago. The procedure and immediate aftermath were uneventful. She has hypertension and osteoarthritis. Current medications include glucosamine, amlodipine, and meloxicam. Her temperature is 37.9°C (100.2°F), pulse is 95/min, and blood pressure is 115/70 mm Hg. Examination shows a tender, swollen right knee joint; range of motion is limited by pain. The remainder of the examination shows no abnormalities. Arthrocentesis of the right knee is performed. Analysis of the synovial fluid shows:
Appearance Cloudy
Viscosity Absent
WBC count 78,000/mm3
Segmented neutrophils 94%
Lymphocytes 6%
Synovial fluid is sent for culture and antibiotic sensitivity. Which of the following is the most likely causal pathogen?
- A. Staphylococcus aureus
- B. Escherichia coli
- C. Pseudomonas aeruginosa
- D. Staphylococcus epidermidis (Correct Answer)
- E. Streptococcus agalactiae
Biofilms in device-related infections Explanation: ***Staphylococcus epidermidis***
- This patient's symptoms (worsening pain and swelling in a knee with a history of **total knee arthroplasty 5 months ago**, increased WBC count and neutrophil predominance in synovial fluid), point towards a **prosthetic joint infection**.
- **Coagulase-negative Staphylococci**, particularly *S. epidermidis*, are the most common cause of **late prosthetic joint infections**, typically occurring months to years after surgery.
*Staphylococcus aureus*
- *Staphylococcus aureus* is a common cause of **acute prosthetic joint infections**, which usually manifest within the **first 3 months post-surgery**. This patient's symptoms began 5 months after surgery.
- While it can cause late infections, *S. epidermidis* is more characteristic for this timeline in prosthetic joint infections.
*Escherichia coli*
- *Escherichia coli* is typically associated with **urinary tract infections** or **gastrointestinal infections**.
- It is an uncommon cause of prosthetic joint infections unless there's a direct spread from a local infection or systemic sepsis, which is not suggested here.
*Pseudomonas aeruginosa*
- *Pseudomonas aeruginosa* is often associated with **healthcare-associated infections**, particularly in immunocompromised patients or those with indwelling catheters or extensive burns.
- While it can cause prosthetic joint infections, it's less common than Staphylococci and usually linked to specific clinical settings or water contamination.
*Streptococcus agalactiae*
- *Streptococcus agalactiae* (Group B Strep) is primarily known to cause serious infections in **neonates** and **pregnant women**, and in adults with underlying conditions like **diabetes** or **immunocompromise**.
- It is an infrequent cause of prosthetic joint infections in otherwise healthy adults without specific risk factors for GBS infection.
Biofilms in device-related infections US Medical PG Question 6: A 54-year-old man comes to the physician because of persistent right knee pain and swelling for 2 weeks. Six months ago, he had a total knee replacement because of osteoarthritis. His temperature is 38.5°C (101.3°F), pulse is 100/min, and blood pressure is 139/84 mm Hg. Examination shows warmth and erythema of the right knee; range of motion is limited by pain. His leukocyte count is 14,500/mm3, and erythrocyte sedimentation rate is 50 mm/hr. Blood cultures grow gram-positive, catalase-positive cocci. These bacteria grow on mannitol salt agar without color change. Production of which of the following is most important for the organism's virulence?
- A. Vi capsule
- B. Exotoxin A
- C. Cord factor
- D. Exopolysaccharides (Correct Answer)
- E. Protein A
Biofilms in device-related infections Explanation: ***Exopolysaccharides***
- The patient presents with **fever**, **joint pain and swelling**, elevated **leukocyte count** and **ESR**, and a history of **total knee replacement**, all indicative of a **prosthetic joint infection**.
- The pathogen is described as **gram-positive**, **catalase-positive cocci** that grow on mannitol salt agar without a color change, suggesting **Staphylococcus epidermidis** or a similar coagulase-negative Staphylococcus species. These pathogens are known for forming **biofilms (exopolysaccharides)** on foreign bodies, making treatment difficult.
*Vi capsule*
- The **Vi capsule** is a virulence factor primarily associated with **Salmonella typhi**, which causes typhoid fever.
- The clinical presentation and microbiological findings (gram-positive cocci) do not match **Salmonella typhi** infection.
*Exotoxin A*
- **Exotoxin A** is a potent virulence factor produced by **Pseudomonas aeruginosa**, a gram-negative rod.
- The bacterial description in the stem (gram-positive, catalase-positive cocci) is inconsistent with **Pseudomonas aeruginosa**.
*Cord factor*
- **Cord factor** is a mycolic acid-containing glycolipid found in the cell wall of **Mycobacterium tuberculosis** and other mycobacteria.
- The pathogen in this case is described as **gram-positive cocci**, which rules out a mycobacterial infection.
*Protein A*
- **Protein A** is a cell wall component of **Staphylococcus aureus** that binds to the Fc region of IgG, inhibiting opsonization and phagocytosis.
- While *Staphylococcus aureus* is a gram-positive, catalase-positive cocci, its typical growth on mannitol salt agar involves **yellowing (fermentation of mannitol)** due to acid production, which is not described here ("without color change").
Biofilms in device-related infections US Medical PG Question 7: A 20-year-old woman presents for a follow-up visit with her physician. She has a history of cystic fibrosis and is currently under treatment. She has recently been struggling with recurrent bouts of cough and foul-smelling, mucopurulent sputum over the past year. Each episode lasts for about a week or so and then subsides. She does not have a fever or chills during these episodes. She has been hospitalized several times for pneumonia as a child and continues to struggle with diarrhea. Physically she appears to be underweight and in distress. Auscultation reveals reduced breath sounds on the lower lung fields with prominent rhonchi. Which of the following infectious agents is most likely associated with the recurrent symptoms this patient is experiencing?
- A. Mycobacterium avium
- B. Pseudomonas (Correct Answer)
- C. Histoplasma
- D. Pneumococcus
- E. Listeria
Biofilms in device-related infections Explanation: ***Pseudomonas***
- **Pseudomonas aeruginosa** is a common and opportunistic pathogen in patients with **cystic fibrosis** due to altered mucus secretion and impaired mucociliary clearance.
- Recurrent cough, foul-smelling, and **mucopurulent sputum** are classic symptoms of **Pseudomonas** lung infections in CF patients, often leading to chronic colonization and bronchiectasis.
*Mycobacterium avium*
- While *Mycobacterium avium complex* (MAC) can infect patients with cystic fibrosis, it typically causes a **more indolent and chronic lung disease** rather than recurrent, self-limiting bouts of cough and sputum.
- MAC infections are often associated with **nodular or cavitary lesions** on imaging and may require prolonged multidrug therapy.
*Histoplasmosis*
- **Histoplasmosis** is a fungal infection endemic to certain geographic regions (e.g., Ohio and Mississippi River valleys) and is acquired by inhaling spores.
- It's **not a typical or recurrent pathogen** in cystic fibrosis patients in the way bacterial infections are, and its presentation often includes fever, chills, and disseminated disease in immunocompromised individuals.
*Pneumococcus*
- *Streptococcus pneumoniae* (**Pneumococcus**) is a common cause of **acute bacterial pneumonia** in the general population, including young children.
- While CF patients can get pneumococcal infections, the pattern of **recurrent bouts of foul-smelling mucopurulent sputum** without fever and the chronic nature of the lung disease point away from typical acute pneumococcal infection and more towards a chronic colonizer like *Pseudomonas*.
*Listeria*
- *Listeria monocytogenes* is primarily a cause of **foodborne illness**, leading to gastroenteritis, meningitis, or sepsis, particularly in immunocompromised individuals, pregnant women, and neonates.
- It is **not a common respiratory pathogen**, and its presentation does not align with the described recurrent pulmonary symptoms in a cystic fibrosis patient.
Biofilms in device-related infections US Medical PG Question 8: A 45-year-old male presents to his primary care physician complaining of drainage from his left great toe. He has had an ulcer on his left great toe for over eight months. He noticed increasing drainage from the ulcer over the past week. His past medical history is notable for diabetes mellitus on insulin complicated by peripheral neuropathy and retinopathy. His most recent hemoglobin A1c was 9.4%. He has a 25 pack-year smoking history. He has multiple sexual partners and does not use condoms. His temperature is 100.8°F (38.2°C), blood pressure is 150/70 mmHg, pulse is 100/min, and respirations are 18/min. Physical examination reveals a 1 cm ulcer on the plantar aspect of the left great toe surrounded by an edematous and erythematous ring. Exposed bone can be palpated with a probe. There are multiple small cuts and bruises on both feet. A bone biopsy reveals abundant gram-negative rods that do not ferment lactose. The pathogen most likely responsible for this patient’s current condition is also strongly associated with which of the following conditions?
- A. Otitis externa (Correct Answer)
- B. Waterhouse-Friedrichsen syndrome
- C. Gastroenteritis
- D. Toxic shock syndrome
- E. Rheumatic fever
Biofilms in device-related infections Explanation: ***Otitis externa***
- The patient's presentation with a chronic **diabetic foot ulcer** with exposed bone and **gram-negative, non-lactose fermenting rods** on bone biopsy indicates **osteomyelitis** caused by ***Pseudomonas aeruginosa***.
- ***Pseudomonas aeruginosa*** is strongly associated with **otitis externa** (swimmer's ear), particularly **malignant otitis externa** in diabetic and immunocompromised patients.
- This is a classic association tested on USMLE: *Pseudomonas* causes both diabetic foot osteomyelitis and otitis externa.
*Waterhouse-Friedrichsen syndrome*
- This syndrome involves adrenal hemorrhage and fulminant sepsis, classically caused by ***Neisseria meningitidis***.
- Not associated with *Pseudomonas aeruginosa*.
*Gastroenteritis*
- Primarily caused by enteric pathogens such as *Salmonella*, *Shigella*, *Campylobacter*, *E. coli*, or viral agents.
- *Pseudomonas aeruginosa* is not a typical cause of gastroenteritis.
*Toxic shock syndrome*
- Caused by exotoxins from ***Staphylococcus aureus*** (TSST-1) or **Group A Streptococcus** (pyrogenic exotoxins).
- Not associated with *Pseudomonas aeruginosa*.
*Rheumatic fever*
- A delayed autoimmune complication of **Group A Streptococcal pharyngitis**.
- Not related to *Pseudomonas* infections or diabetic foot ulcers.
Biofilms in device-related infections US Medical PG Question 9: 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
Biofilms in device-related infections 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.
Biofilms in device-related infections US Medical PG Question 10: A 47-year-old man presents to the emergency department with jaundice and extreme fatigue for the past 4 days. He also noticed that his stool is very pale and urine is dark. Past medical history is unremarkable. The review of systems is significant for a 23 kg (50 lb) weight loss over the last 3 months which he says is due to decreased appetite. He is afebrile and the vital signs are within normal limits. A contrast computed tomography (CT) scan of the abdomen reveals a mass in the pancreatic head. A blood test for carbohydrate antigen (CA19-9) is positive. The patient is admitted to the intensive care unit (ICU) and undergoes surgical decompression of the biliary tract. He is placed on total parenteral nutrition (TPN). On day 4 after admission, his intravenous access site is found to be erythematous and edematous. Which of the following microorganisms is most likely responsible for this patient’s intravenous (IV) site infection?
- A. Candida parapsilosis (Correct Answer)
- B. E. coli
- C. Hepatitis B virus
- D. Pseudomonas aeruginosa
- E. Malassezia furfur
Biofilms in device-related infections Explanation: ***Candida parapsilosis***
- This yeast is a common cause of **catheter-related bloodstream infections** in patients receiving **total parenteral nutrition (TPN)**, as it can readily grow on lipid emulsions.
- The patient's presentation with an erythematous and edematous intravenous access site, coupled with a history of TPN, strongly points towards a fungal infection, with *C. parapsilosis* being a primary suspect due to its affinity for TPN.
*E. coli*
- While *E. coli* is a common cause of **urinary tract infections** and can cause **bloodstream infections**, it is not a typical cause of IV site infections specifically associated with TPN.
- Its presence at an IV site would usually indicate a more generalized sepsis or contamination, rather than the specific affinity *C. parapsilosis* has for TPN lines.
*Hepatitis B virus*
- **Hepatitis B virus** causes **viral hepatitis** and liver damage, but it does not directly cause localized IV site infections with erythema and edema.
- It is typically spread through blood and body fluids and its clinical manifestations are systemic, primarily involving the liver, rather than local skin signs at an IV access site.
*Pseudomonas aeruginosa*
- **Pseudomonas aeruginosa** is a common opportunistic pathogen, particularly in **immunocompromised patients** and those with medical devices, but it is typically associated with infections in burn wounds, cystic fibrosis, or ventilator-associated pneumonia.
- While it can cause catheter-related infections, it is not as uniquely linked to TPN-associated IV site infections as *Candida parapsilosis*.
*Malassezia furfur*
- *Malassezia furfur* is known to cause **catheter-related infections** in patients receiving **lipid emulsions** via central lines, similar to *C. parapsilosis*.
- However, *C. parapsilosis* is statistically a more common cause of TPN-associated fungemia and IV site infections than *M. furfur*.
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