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Infection, Pharmacology & VTE MCQs

Practice Set 50 of 68

This practice set contains high-yield board review questions covering key concepts in Infection, Pharmacology & VTE. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 981

Topic: Infection, Pharmacology & VTE

In prosthetic joint infections, Staphylococcus epidermidis evades the host immune system and antibiotic therapy by forming a robust biofilm. Which specific substance constitutes the primary structural backbone of this biofilm?

. Polysaccharide intercellular adhesin (PIA)
. Peptidoglycan
. Lipopolysaccharide (LPS)
. Teichoic acid
. Hyaluronic acid

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Polysaccharide intercellular adhesin (PIA), also known as poly-N-acetylglucosamine (PNAG), is the main exopolysaccharide secreted by S. epidermidis. It forms the slimy extracellular polymeric matrix that cements the biofilm to the implant surface.

Question 982

Topic: Infection, Pharmacology & VTE
Rivaroxaban is frequently prescribed for deep vein thrombosis (DVT) prophylaxis following total joint arthroplasty. What is its precise mechanism of action in the coagulation cascade?
. Direct thrombin (Factor IIa) inhibitor
. Indirect Factor Xa inhibitor via potentiation of antithrombin III
. Direct Factor Xa inhibitor
. Vitamin K epoxide reductase inhibitor
. Adenosine diphosphate (ADP) receptor antagonist

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban and Apixaban are Direct Oral Anticoagulants (DOACs) that work by directly and reversibly inhibiting Factor Xa. Unlike low-molecular-weight heparins, they do not require antithrombin III to exert their effect.

Question 983

Topic: Infection, Pharmacology & VTE

During a two-stage exchange arthroplasty for a periprosthetic joint infection caused by methicillin-resistant Staphylococcus aureus, rifampin is often added to the antibiotic regimen due to its biofilm penetration. What is the mechanism of action of rifampin?

. Inhibition of cell wall synthesis
. Binding to the 30S ribosomal subunit
. Binding to the 50S ribosomal subunit
. Inhibition of DNA gyrase
. Inhibition of DNA-dependent RNA polymerase

Correct Answer & Explanation

. Inhibition of cell wall synthesis

Explanation

Rifampin works by binding to and inhibiting bacterial DNA-dependent RNA polymerase, thereby preventing transcription of messenger RNA. It is highly effective against staphylococci residing in biofilms.

Question 984

Topic: Infection, Pharmacology & VTE
Which of the following best describes the primary mechanism of action of rivaroxaban used for VTE prophylaxis following total joint arthroplasty?
. Direct, reversible inhibition of thrombin (Factor IIa)
. Indirect inhibition of Factor Xa via antithrombin III activation
. Direct, selective inhibition of Factor Xa
. Irreversible inhibition of ADP-induced platelet aggregation
. Inhibition of vitamin K epoxide reductase

Correct Answer & Explanation

. Direct, selective inhibition of Factor Xa

Explanation

Rivaroxaban and Apixaban are direct oral anticoagulants (DOACs) that act as direct, highly selective, reversible inhibitors of Factor Xa. Dabigatran is a direct thrombin (IIa) inhibitor. Low-molecular-weight heparin (LMWH) indirectly inhibits Factor Xa by binding to antithrombin III. Warfarin inhibits vitamin K epoxide reductase.

Question 985

Topic: Infection, Pharmacology & VTE

Which phase of bacterial biofilm formation is characterized by the production of a dense extracellular polymeric substance (EPS) matrix and active quorum sensing?

. Initial reversible attachment
. Irreversible attachment
. Maturation
. Dispersion
. Planktonic proliferation

Correct Answer & Explanation

. Initial reversible attachment

Explanation

Biofilm formation occurs in stages: 1) Initial reversible attachment. 2) Irreversible attachment (via adhesins). 3) Maturation, where bacteria multiply, produce a dense extracellular polymeric substance (EPS - 'glycocalyx'), and engage in cell-to-cell communication known as quorum sensing. 4) Dispersion/Detachment, where bacteria release planktonic cells to spread infection.

Question 986

Topic: Infection, Pharmacology & VTE

What is the most common pathogen for soft-tissue infection of the foot caused by a puncture wound?

. Staphylococcus aureus
. Pseudomonas aeruginosa
. Eikenella corrodens
. Pasteurella multocida
. Vibrio species

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Staphylococcus and Streptococcus species are the most common causes of soft-tissue infections in the foot due to punctures. Pseudomonas is the most common cause of osteomyelitis of the foot due to puncture wounds. Pasteurella and Eikenella are seen in animal and human bites, respectively.Vibrio species are found in marine environments.

Question 987

Topic: Infection, Pharmacology & VTE

In the pathogenesis of periprosthetic joint infections, bacteria often form a biofilm that renders them highly resistant to host defenses and systemic antibiotics. Which of the following best describes the 'quorum sensing' phase of biofilm formation?

. Reversible attachment of planktonic bacteria to the implant surface via van der Waals forces
. Irreversible attachment mediated by bacterial adhesins like fibronectin-binding proteins
. Cell-to-cell communication regulating gene expression and extracellular polymeric substance (EPS) production
. Dispersal of planktonic bacteria from the mature biofilm to colonize new sites
. Phagocytosis evasion through the immediate shedding of surface antigens

Correct Answer & Explanation

. Reversible attachment of planktonic bacteria to the implant surface via van der Waals forces

Explanation

Quorum sensing is a density-dependent mechanism of bacterial cell-to-cell communication. As bacterial density increases, autoinducers are released. Upon reaching a critical threshold, this triggers coordinated changes in gene expression across the population, leading to massive production of the extracellular polymeric substance (EPS) matrix and biofilm maturation.

Question 988

Topic: Infection, Pharmacology & VTE
A 28-year-old professional athlete sustains an acute knee injury. Physical examination reveals gross valgus laxity at both 30 degrees and 0 degrees of flexion. MRI confirms an isolated Grade III tear of the medial collateral ligament (MCL), specifically noting a distal avulsion of the superficial MCL from the tibia, with the torn ligament end displaced superficial to the pes anserinus tendons. What is the most appropriate management strategy for this specific injury pattern?
. Hinged knee brace and functional rehabilitation for 6 weeks
. Acute surgical repair or reconstruction of the MCL
. Casting the knee in 30 degrees of flexion for 4 weeks
. Corticosteroid injection at the tibial insertion followed by progressive weight bearing
. Arthroscopic meniscectomy and observation of the MCL

Correct Answer & Explanation

. Acute surgical repair or reconstruction of the MCL

Explanation

While the vast majority of isolated MCL tears (even Grade III) can be treated nonoperatively with hinged bracing, a distal tibial avulsion of the superficial MCL that flips superficial to the pes anserinus tendons creates an 'MCL Stener-like lesion.' Because the pes anserinus physically blocks the torn MCL from anatomically resting against its tibial insertion footprint, healing is prohibited. Therefore, this specific pattern is an absolute indication for acute surgical repair.

Question 989

Topic: Infection, Pharmacology & VTE

A 14-year-old boy presents with a rigid flatfoot and recurrent ankle sprains. Radiographs show a continuous C-shaped bony outline involving the medial talar dome and the posteroinferior aspect of the sustentaculum tali. Which of the following is true regarding this patient's condition?

. The deformity typically involves a cavovarus posture.
. It is best visualized on a 45-degree internal oblique radiograph.
. The 'C-sign' is a radiographic indicator of a talocalcaneal coalition.
. Excision of the coalition is indicated regardless of the percentage of joint involvement.
. It is significantly more common than a calcaneonavicular coalition.

Correct Answer & Explanation

. The deformity typically involves a cavovarus posture.

Explanation

The 'C-sign' on a lateral radiograph is formed by the continuous outline of the medial talar dome and the posteroinferior aspect of the sustentaculum tali, strongly indicating a talocalcaneal coalition. Calcaneonavicular coalitions are best seen on a 45-degree internal oblique radiograph. Talocalcaneal coalitions typically present with a rigid pes planovalgus deformity. Resection is generally reserved for coalitions involving less than 50% of the posterior facet.

Question 990

Topic: Infection, Pharmacology & VTE

In the pathogenesis of periprosthetic joint infections, bacterial biofilm formation significantly complicates non-operative eradication. Which of the following mechanisms is the primary reason biofilm-associated bacteria are highly resistant to systemic beta-lactam antibiotics?

. Enzymatic degradation of antibiotics within the glycocalyx
. Decreased metabolic activity and division rate of sessile bacteria
. Upregulation of generalized cellular efflux pumps
. Rapid horizontal gene transfer of resistance plasmids within the biofilm
. Altered target site affinity on the bacterial cell wall

Correct Answer & Explanation

. Enzymatic degradation of antibiotics within the glycocalyx

Explanation

While biofilms utilize several mechanisms to resist clearance (including acting as a physical barrier), the most significant factor conferring profound resistance to systemic antibiotics (especially beta-lactams, which target actively dividing cell walls) is the altered metabolic state of the bacteria. Bacteria deep in the biofilm exist in a stationary, sessile phase with very low metabolic activity and virtually no division, rendering cell-wall targeting agents largely ineffective.

Question 991

Topic: Infection, Pharmacology & VTE

Orthopedic implant infections are notoriously difficult to eradicate due to biofilm formation. Within a mature biofilm, bacteria coordinate their behavior, alter gene expression, and increase virulence based on local population density. What is the term for this cell-to-cell communication mechanism?

. Chemotaxis
. Quorum sensing
. Phagocytosis evasion
. Planktonic transition
. Glycocalyx shedding

Correct Answer & Explanation

. Chemotaxis

Explanation

Quorum sensing is the process by which bacteria communicate chemically within a biofilm, allowing them to detect population density and coordinate gene expression. This leads to increased virulence and profound resistance to systemic antibiotics.

Question 992

Topic: Infection, Pharmacology & VTE

A 72-year-old male develops a chronic periprosthetic joint infection caused by Staphylococcus epidermidis. The pathogenesis of this infection relies heavily on bacterial adherence and biofilm formation. Which component is crucial for the initial irreversible attachment phase of this organism to the implant?

. Lipopolysaccharide
. Polysaccharide intercellular adhesin (PIA)
. Protein A
. Hyaluronidase
. Coagulase

Correct Answer & Explanation

. Lipopolysaccharide

Explanation

Staphylococcus epidermidis produces polysaccharide intercellular adhesin (PIA), which is essential for cell-to-cell adhesion and the formation of the protective biofilm matrix. This makes eradication of the implant-associated infection extremely difficult without hardware removal.

Question 993

Topic: Infection, Pharmacology & VTE
A patient undergoing total knee arthroplasty is prescribed enoxaparin for deep vein thrombosis prophylaxis. What is the primary molecular target by which enoxaparin exerts its anticoagulant effect?
. Direct inhibition of thrombin (Factor IIa)
. Vitamin K epoxide reductase
. Antithrombin III, leading to preferential inhibition of Factor Xa
. Inhibition of ADP binding to the P2Y12 receptor
. Inactivation of Factor VIIIa and Va via Protein C

Correct Answer & Explanation

. Antithrombin III, leading to preferential inhibition of Factor Xa

Explanation

Enoxaparin, a low-molecular-weight heparin (LMWH), binds to antithrombin III. This complex primarily inhibits Factor Xa (with a much higher ratio of anti-Xa to anti-IIa activity compared to unfractionated heparin), effectively preventing clot formation.

Question 994

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for deep vein thrombosis prophylaxis following a total hip arthroplasty. What is the precise mechanism of action of this pharmacological agent?
. Directly inhibits thrombin (Factor IIa)
. Enhances antithrombin III activity against Factor Xa
. Competitively inhibits vitamin K epoxide reductase
. Directly inhibits activated Factor X (Factor Xa)
. Inhibits ADP-induced platelet aggregation

Correct Answer & Explanation

. Directly inhibits activated Factor X (Factor Xa)

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants that work by directly inhibiting Factor Xa, interrupting the common pathway of the coagulation cascade. Unlike heparins, they do not require antithrombin III for their activity.

Question 995

Topic: Infection, Pharmacology & VTE
A 22-year-old football running back sustains a grade III medial collateral ligament (MCL) tear. MRI demonstrates an avulsion of the MCL from its distal tibial attachment, with the pes anserinus tendons interposed between the torn ligament and the bone. What is the most appropriate management?
. Protected weight bearing in a hinged knee brace for 6 weeks
. Acute surgical repair of the MCL
. Corticosteroid injection and early range of motion
. Delayed MCL reconstruction at 3 months
. Platelet-rich plasma injection and physical therapy

Correct Answer & Explanation

. Acute surgical repair of the MCL

Explanation

This describes a "Stener-like lesion" of the knee, where the pes anserinus blocks reduction of the distally avulsed MCL to its footprint. This prevents spontaneous healing and is an absolute indication for acute surgical repair.

Question 996

Topic: Infection, Pharmacology & VTE

During a medial approach to the proximal tibia, the pes anserinus is encountered. Which of the following represents the correct anterior-to-posterior orientation of the tendinous insertions forming the pes anserinus?

. Sartorius, Gracilis, Semitendinosus
. Gracilis, Sartorius, Semitendinosus
. Semitendinosus, Gracilis, Sartorius
. Sartorius, Semitendinosus, Gracilis
. Gracilis, Semitendinosus, Sartorius

Correct Answer & Explanation

. Sartorius, Gracilis, Semitendinosus

Explanation

The pes anserinus ('goose foot') consists of the combined tendinous insertions of the Sartorius, Gracilis, and Semitendinosus on the proximal anteromedial tibia. They insert in that exact anterior-to-posterior and proximal-to-distal order. A common mnemonic is 'Say Grace Before Tea' (Sartorius, Gracilis, Semitendinosus).

Question 997

Topic: Infection, Pharmacology & VTE
A 5-year-old boy presents with a 3-day history of right hip pain, refusal to bear weight, a temperature of 38.8°C, and an ESR of 55 mm/hr. Joint aspiration yields synovial fluid with a WBC count of 85,000/mm3 (>90% PMNs). After surgical irrigation and debridement, what is the most appropriate empirical intravenous antibiotic therapy pending culture results in an area with a 20% rate of community-acquired MRSA?
. Cefazolin monotherapy
. Ceftriaxone and Clindamycin
. Ampicillin and Gentamicin
. Vancomycin or Clindamycin
. Oral Amoxicillin-Clavulanate

Correct Answer & Explanation

. Vancomycin or Clindamycin

Explanation

Staphylococcus aureus is the most common cause of septic arthritis in children >3 months. Empirical therapy must target S. aureus. In areas where community-acquired MRSA prevalence exceeds 10-15%, anti-MRSA coverage such as Clindamycin or Vancomycin should be utilized as the first-line empiric agent pending culture sensitivities.

Question 998

Topic: Infection, Pharmacology & VTE

The Kocher criteria are used to differentiate pediatric septic arthritis from transient synovitis. Which additional laboratory marker was later added by Caird et al. to increase the predictive value of the original criteria?

. Procalcitonin > 0.5 ng/mL
. C-reactive protein (CRP) > 2.0 mg/dL
. D-dimer > 500 ng/mL
. Interleukin-6 > 10 pg/mL
. Lactate dehydrogenase (LDH) > 250 U/L

Correct Answer & Explanation

. Procalcitonin > 0.5 ng/mL

Explanation

Caird et al. added CRP > 2.0 mg/dL to the original four Kocher criteria (fever, non-weight-bearing, ESR > 40, WBC > 12,000). The presence of all five parameters predicts a >97% probability of septic arthritis.

Question 999

Topic: Infection, Pharmacology & VTE

According to the Kocher criteria, which combination of clinical findings yields a 99% predictive probability for septic arthritis of the hip in a pediatric patient?

. Fever >38.5 C, inability to bear weight, ESR >40 mm/hr, WBC >12,000 cells/mm3
. Fever >38.0 C, positive blood culture, CRP >2 mg/dL, joint effusion
. Limp, night pain, morning stiffness, ESR >20 mm/hr
. Inability to bear weight, CRP >1 mg/dL, WBC >10,000 cells/mm3, recent URI
. Fever >39.0 C, refusal to walk, hip held in external rotation, negative plain films

Correct Answer & Explanation

. Fever >38.5 C, inability to bear weight, ESR >40 mm/hr, WBC >12,000 cells/mm3

Explanation

The Kocher criteria include non-weight-bearing status, temperature >38.5 C, ESR >40 mm/hr, and WBC >12,000 cells/mm3. The presence of all four criteria indicates a 99% probability of septic arthritis over transient synovitis.

Question 1000

Topic: Infection, Pharmacology & VTE

A 2-year-old child presents to the emergency department with an acute limp and refusal to bear weight on the right leg. There is a low-grade fever and a recent history of an upper respiratory tract infection. Joint aspiration reveals purulent fluid. Gram stain is initially negative. Which of the following organisms is a fastidious Gram-negative coccobacillus that is a leading cause of osteoarticular infections in this specific age group?

. Staphylococcus aureus
. Streptococcus pneumoniae
. Kingella kingae
. Haemophilus influenzae type b
. Neisseria gonorrhoeae

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Kingella kingae is a fastidious Gram-negative coccobacillus and a leading cause of septic arthritis and osteomyelitis in children aged 6 months to 4 years. It often follows an upper respiratory infection (stomatitis or pharyngitis). It is difficult to isolate on routine solid culture media; detection rates are significantly improved by inoculating joint fluid into blood culture vials or using PCR.

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