Oral Infection and Immunity, Including Oral Microbiology
Domain 8 tests the microbiology of common oral infections, the immune response that contains them, and the principles of antimicrobial stewardship and infection control. The exam favors questions that distinguish viral, fungal, and bacterial disease and that avoid unnecessary antibiotics.
Oral microbiome and biofilm
- The oral cavity contains more than 700 bacterial species organized in biofilms.
- Caries is associated with Streptococcus mutans and Lactobacillus species.
- Periodontitis is associated with Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Treponema denticola, and Tannerella forsythia.
- Candida albicans is a commensal that overgrows with antibiotics, corticosteroids, xerostomia, diabetes, and HIV.
- Herpes simplex virus type 1 establishes latency in the trigeminal ganglion and reactivates with stress, ultraviolet light, or immunosuppression.
- HPV is associated with oropharyngeal squamous cell carcinoma.
Immunity
- Innate defenses include the epithelial barrier, saliva with IgA, lysozyme, and lactoferrin, and neutrophils.
- Adaptive immunity involves T cells, B cells, and secretory IgA.
- Immunosuppression from HIV, transplantation, or chemotherapy increases risk of candidiasis, herpes, and periodontal disease.
Infection control and stewardship
- Standard precautions and sterilization of instruments prevent transmission.
- Antibiotic prophylaxis for infective endocarditis is reserved for high-risk cardiac conditions; amoxicillin 2 g is given 30 to 60 minutes before the procedure when indicated.
- Avoid antibiotics for viral infections and uncomplicated aphthous ulcers.
Worked example
A 28-year-old student has recurrent painful vesicles on the upper lip before examinations. The prodrome and clustered vesicles suggest herpes labialis. Diagnosis is clinical; topical acyclovir or oral valacyclovir can be used early. Antibiotics are not indicated. Counsel on triggers and hand hygiene.
Traps that cost marks
- Prescribing antibiotics for aphthae or herpes.
- Missing HIV infection in a patient with recurrent candidiasis.
- Not considering candidiasis in a patient using inhaled corticosteroids.
- Using the wrong endocarditis prophylaxis regimen.
- Ignoring antimicrobial resistance and stewardship.