Microbiology and Immunology
Microbiology and immunology: what is tested
Questions target oral microbial ecology, odontogenic and periodontal pathogens, infection control, and the immune mechanisms relevant to oral disease and vaccination.
Core rules
- Caries initiation is linked to mutans streptococci, especially Streptococcus mutans; Lactobacillus is associated with progression; root caries involves Actinomyces.
- Periodontal red complex: Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola. Aggregatibacter actinomycetemcomitans is linked to localized aggressive periodontitis.
- Viridans streptococci are the classic cause of subacute infective endocarditis after dental procedures.
- Salivary antibody is mainly secretory IgA; serum immunity is mainly IgG.
- Hypersensitivity: type I IgE, type II antibody-mediated, type III immune complex, type IV T-cell mediated.
- Autoclaving at 121 degrees C for 15 minutes or 134 degrees C for 3 minutes sterilizes; Geobacillus stearothermophilus spores test steam sterilization.
- Glutaraldehyde is a high-level disinfectant; alcohol is not a sterilant.
Worked example
An unvaccinated dental worker sustains a needlestick from an HBsAg-positive patient. Reasoning: hepatitis B is a DNA virus and is stable in dried blood, so transmission risk is real. Management is immediate washing, then hepatitis B immunoglobulin plus start of vaccination series. If the worker had documented anti-HBs above 10 mIU/mL, no immunoglobulin would be needed.
Traps
- Naming Lactobacillus as the initiator of caries rather than the progressor.
- Confusing type IV hypersensitivity with antibody-mediated reactions.
- Assuming alcohol wipes sterilize instruments; they do not.
- Forgetting that hepatitis B is a DNA virus, unlike hepatitis C.