MCQs – Infections 2

Modern Study Review (AI-Generated)

High-Yield Summary

This topic is a staple of the Royal College exam, focusing heavily on infectious musculoskeletal conditions and their management, including osteomyelitis, soft tissue infections, and pathogen-specific treatments. The single most important clinical trade-off is early recognition and timely antibiotic/debridement intervention versus risk of chronic infection or systemic toxicity. The examiner often forces a choice between empiric broad-spectrum coverage and pathogen-directed therapy based on clinical context and microbiology. While the exam favors classic antibiotic choices like penicillin for Pasteurella and actinomycosis, modern practice increasingly incorporates broader-spectrum agents and adjunctive therapies such as hyperbaric oxygen for gas gangrene.

High-Yield Decision Matrix

Active Recall Q&A

Infectious Pathogenesis and Imaging

Q: What role do immune complexes play in Lyme disease?
A: Immune complexes are part of the pathogenesis of Lyme disease.
Related Pearl: Immune complex deposition contributes to Lyme arthritis, causing joint inflammation and swelling.

Q: What is a characteristic x-ray finding in Charcot joints caused by syphilis?
A: Exuberant heterotopic bone formation is characteristic.
Related Pearl: This exuberant bone formation helps differentiate syphilitic Charcot joints from diabetic neuropathic joints, which typically show bone resorption.

Cat Bite Infections

Q: Which pathogen should be suspected in infections following cat bites?
A: Pasteurella multocida, a gram-negative aerobic rod.
Related Pearl: Despite its gram-negative classification, Pasteurella multocida is uniquely sensitive to penicillin, unlike many other gram-negative rods.

Q: What is the recommended antibiotic treatment for cat bite infections caused by Pasteurella multocida?
A: Penicillin is the treatment of choice.
Related Pearl: Early penicillin administration prevents progression to cellulitis, abscess, or systemic infection.

Drug Toxicity Profiles

Q: What are the toxicities associated with erythromycin?
A: Erythromycin is both ototoxic and hepatotoxic.
Related Pearl: Monitor liver enzymes and auditory function during prolonged erythromycin therapy to prevent irreversible damage.

Q: What is the primary toxicity concern with most aminoglycosides?
A: Nephrotoxicity is the main concern.
Related Pearl: Renal function must be closely monitored; dosing adjustments are critical to avoid acute kidney injury.

Q: What visual side effects can fluoroquinolones cause?
A: Fluoroquinolones can cause visual problems.
Related Pearl: Visual disturbances such as blurred vision or photophobia may necessitate drug discontinuation.

Severe Soft Tissue Infections

Q: What is the standard treatment approach for gas gangrene?
A: Extensive debridement or amputation, penicillin administration, and hyperbaric oxygen therapy.
Related Pearl: Hyperbaric oxygen enhances leukocyte killing and inhibits anaerobic bacterial growth, improving survival.

Q: Which organism most commonly causes necrotizing fasciitis?
A: Alpha hemolytic streptococcus.
Related Pearl: Early aggressive surgical debridement combined with antibiotics is essential to reduce mortality.

Q: What antibiotic is a good choice for multibug infections of the foot?
A: Clindamycin.
Related Pearl: Clindamycin covers gram-positive cocci and anaerobes, common in polymicrobial foot infections, including diabetic foot ulcers.

Microbiology and Osteomyelitis

Q: What does the appearance of gram-positive spore-forming rods indicate?
A: It is very concerning for Clostridium perfringens infection.
Related Pearl: Clostridium perfringens produces potent exotoxins causing rapid tissue necrosis and systemic toxicity.

Q: How does delay in treating acute osteomyelitis affect prognosis?
A: Longer delay increases the risk of developing chronic osteomyelitis.
Related Pearl: Early diagnosis and treatment within days can prevent irreversible bone necrosis and chronic infection.

Special Considerations

Q: Why should flagyl be used cautiously in patients with liver disease?
A: Because flagyl has hepatotoxic potential.
Related Pearl: Impaired liver function reduces drug metabolism, increasing risk of toxicity and adverse effects.

Q: Is actinomycosis a fungal infection?
A: No, actinomycosis is caused by gram-positive bacteria, not fungi.
Related Pearl: Misclassification as fungal infection delays appropriate antibiotic therapy, worsening outcomes.

Q: What is the treatment of choice for actinomycosis?
A: Penicillin.
Related Pearl: Prolonged high-dose penicillin therapy is often required due to the chronic, indolent nature of the infection.

Classic Clinical Notes

• Immune complexes are part of the pathogenesis of lyme disease
• In Charcot joints from syphyllis, a characteristic x-ray finding is exuberant heterotopic bone.
• In patients with cat bites and infection, think pasteurella multicidans, and treat with penicillin, even though it is a gram negative aerobic rod.
• Erythromycin is both ototoxic and hepatotoxic.
• Most aminoglycosides are nephrotoxic.
• Gas gangrene is treated with extensive debridement/amputation, penicillin, and hyperbaric oxygen.
• Necrotizing fasciitis is most commonly caused by alpha hemolytic strep
• For multibug infections of the foot, clinda is a good choice of antibioitic.
• The appearance of gram positive spore forming rods is very concerning – c. perfringens.
• Length of delay before treating acute osteo is a risk factor for developing chronic osteo.
• In a patient with liver disease, be wary of prescribing flagyl.
• Actinomycosis is NOT a fungus, as the name suggests – it is a gram positive bacteria and has been known to cause osteomyelitis. It is treated with penicillin.
• Flouriquine can cause visual problems.

Last Updated on January 25, 2026 by Christian Veillette