Antimicrobials & Infection Control MCQ

When infection genuinely needs a drug, choosing the right one and using it judiciously is a core dental skill, and preventing cross-infection protects every patient and the whole team. This capstone module ties the microbiology together: the antibiotic classes and how they work, how to select a drug for a dental infection (and when not to prescribe at all), antibiotic prophylaxis for the right patients, the antifungals and antivirals, and the sterilization and infection-control practices that make safe dentistry possible.

Antibiotic Classes and How They Work

• Penicillins and cephalosporins (beta-lactams) inhibit bacterial cell wall (peptidoglycan) synthesis; amoxicillin is the dental workhorse, and adding clavulanate overcomes beta-lactamase resistance.
• Macrolides (azithromycin, erythromycin) and clindamycin bind the 50S ribosomal subunit to block protein synthesis; both are options for penicillin-allergic patients, and clindamycin has useful anaerobic coverage but a notable risk of Clostridioides difficile colitis.
• Metronidazole is bactericidal against anaerobes and is often paired with amoxicillin for periodontal and anaerobic infections; it causes a disulfiram-like reaction with alcohol, so patients must avoid alcohol.
• Tetracyclines (including doxycycline) bind the 30S subunit; they bind calcium in developing teeth and bone, causing permanent tooth discoloration, so they are avoided in pregnancy and in children under about 8 years.

Choosing an Antibiotic in Dentistry, and Stewardship

• Most odontogenic infections are treated by source control (drainage, and removing or treating the offending tooth). Antibiotics are an adjunct for spreading infection, systemic involvement (fever, malaise, cellulitis), or the immunocompromised patient, not a substitute for the procedure.
• When an antibiotic is indicated, amoxicillin is first-line for oral flora; for penicillin-allergic patients, clindamycin or azithromycin are common alternatives (weighing clindamycin's C. difficile risk).
• Metronidazole, often added to amoxicillin, is used for anaerobic periodontal infections such as severe or refractory periodontitis.
• Stewardship means prescribing only when indicated, choosing the narrowest effective drug, and using the right dose for the shortest appropriate course, to limit resistance and adverse effects (C. difficile, candidiasis, allergy).

Antibiotic Prophylaxis

• Endocarditis prophylaxis is reserved for the highest-risk cardiac conditions (prosthetic valve or prosthetic repair material, prior infective endocarditis, certain congenital heart disease, and cardiac transplant valvulopathy) before procedures that manipulate gingiva or the periapical region or perforate the oral mucosa.
• The standard adult regimen is amoxicillin 2 g orally, taken 30 to 60 minutes before the procedure (children 50 mg/kg).
• For penicillin allergy, current options include cephalexin (if no history of anaphylaxis or angioedema to penicillins), or azithromycin or clarithromycin, or doxycycline; clindamycin is no longer recommended for prophylaxis because of its adverse-effect profile.
• For patients with prosthetic joints, routine antibiotic prophylaxis before dental procedures is generally not recommended; decisions for unusual cases are made with the orthopedic surgeon.

Antifungals and Antivirals

• Oral candidiasis is treated with antifungals plus correcting the cause: topical nystatin (swish and swallow) or clotrimazole for localized disease, and systemic fluconazole for more extensive or refractory cases.
• Antifungals target the fungal membrane sterol ergosterol: azoles (fluconazole, clotrimazole) inhibit ergosterol synthesis, while polyenes (nystatin, amphotericin B) bind ergosterol directly. Amphotericin B is reserved for severe systemic mycoses (such as mucormycosis) and is nephrotoxic.
• Acyclovir and related antivirals treat herpes simplex and varicella-zoster infections and work best when started early (in the prodrome); they control outbreaks but do not eliminate the latent virus.
• Because thrush often reflects an underlying problem, treating the Candida without addressing antibiotics, steroids, dentures, dry mouth, diabetes, or immunosuppression invites recurrence.

Sterilization and Infection Control

• Sterilization destroys all microorganisms including spores; disinfection reduces microbes on surfaces (but may spare spores); antisepsis is reducing microbes on living tissue (such as skin or mucosa).
• The autoclave (steam under pressure, typically 121 C) is the standard for sterilizing heat-stable dental instruments because it reliably kills spores; biological (spore) indicators are run to verify the sterilizer is working.
• The Spaulding classification guides reprocessing: critical items that penetrate soft tissue or bone (for example, surgical instruments, scalers) must be sterilized; semicritical items that contact mucosa are sterilized or high-level disinfected; noncritical surfaces are cleaned and disinfected or barrier-protected.
• Standard precautions treat every patient as potentially infectious, using gloves, mask, and eye protection, safe sharps handling, surface barriers and disinfection, hand hygiene, and waterline maintenance, regardless of any known or unknown diagnosis.