Oral Bacteria and Dental Diseases

Bacteria Associated with Dental Caries

• These are facultative or obligate anaerobes
• Actinomyces sp. contribute to the start and progression of caries, specifically root caries
• Streptococcus mutans predominates in dental plaque and is a primary pathogen in dental caries
• S. mutans are acidogenic, producing an enzyme that contributes to plaque's adherent properties
• Aggregatibacter actinomycetemcomitans is a green complex that can invade gingival epithelium, and is associated with aggressive periodontitis
• Fusobacterium sp. are an orange complex, which can act as a bridge between early and late colonizing bacteria in plaque

Bacteria Associated with Periodontal Disease

• These are facultative or obligate anaerobes
• Porphyromonas gingivalis constitutes the red complex, commonly found in subgingival calculus, and is involved in the pathogenesis of chronic periodontitis
• Prevotella intermedia is an orange complex, associated with pregnancy gingivitis and commonly found in periodontal abscesses
• Tannerella forsythia constitutes the red complex, associated with chronic periodontitis
• T. forsythia inhabits subgingival areas, initiating connective tissue destruction and alveolar bone resorption in periodontal disease
• Treponema denticola constitutes the red complex, associated with acute necrotizing ulcerative gingivitis and periodontitis (ANUG/ANUP)

Bacteria Associated with Endodontic Lesions

• Enterococcus faecalis is associated with failed root canals
• E. faecalis resists intracanal medications and irrigants, like calcium hydroxide

Bacteria Associated with Infective Endocarditis

• Staphylococcus aureus is typically a normal skin colonizer
• S. aureus is associated with aggressive and severe infective endocarditis if it enters the bloodstream
• Streptococcus sanguinis is a yellow complex typically associated with healthy plaque biofilm
• S. sanguinis can cause disseminated infection if it enters the bloodstream, including infective endocarditis
• S. sanguinis belongs to the Viridans streptococci

Other Bacteria with Dental Relevance

• Clostridium difficile causes colon infections, frequently after taking antibiotics, and is most often associated with Clindamycin use
• Escherichia coli is found in the intestines of healthy individuals
• E. coli can cause urinary tract infections, colitis, meningitis, and gastroenteritis
• Helicobacter pylori is the main bacterial cause of duodenal ulcers
• Geobacillus stearothermophilus is a thermophilic bacterium resistant to sterilization
• Autoclaves should be tested weekly to ensure effectiveness against spores
• Streptococcus pyogenes, also referred to as group A streptococcus, causes streptococcal pharyngitis (strep throat)
• Rheumatic fever is a common complication of pharyngitis
• S. pyogenes is the most common cause of erysipelas
• Mycobacterium tuberculosis is the causative agent of tuberculosis (TB)
• The Mantoux test, also known as the tuberculin skin test, screens and diagnoses TB
• Pseudomonas aeruginosa is commonly associated with dental water lines and must have dental water lines flushed to prevent biofilm buildup
• P. aeruginosa is resistant to clindamycin
• Treponema pallidum is the causative agent of syphilis

Biofilm

• Biofilms are structured communities of microorganisms that adhere to surfaces and are embedded in a self-produced extracellular matrix
• Dental plaque is the biofilm that forms in the oral cavity
• Cariogenic bacteria in dental plaque consume sucrose for energy metabolism
• As gingivitis progresses and plaque matures, biofilm flora incorporates more spirochetes
• Interproximal surfaces of teeth have the most diverse biofilm in the oral cavity
• Biofilms enable bacteria to withstand antibiotics

Viruses

• Human Immunodeficiency Virus (HIV) is a bloodborne pathogen
• The HIV genome consists of single-stranded RNA, converted to double-stranded DNA by reverse transcriptase for integration into the host genome
• HIV attacks CD4+ T-helper cells
• HIV is suppressed if the viral load is under 200 copies/mL
• Kaposi's sarcoma is a common malignancy associated with HIV
• Acquired Immunodeficiency Syndrome (AIDS) is the latest stage of HIV when the immune system is severely weakened
• Coxsackie virus is more common in children
• Coxsackie virus causes herpangina, blister-like oral lesions on the soft palate or tonsillar pillars
• Oral manifestations of Hepatitis include jaundice, xerostomia, and petechiae
• Hepatitis A is acute and transmitted via the fecal-oral route; usually self-limiting
• Hepatitis B is transmitted via bodily fluids
  • There is a 30% chance of transfer after a needlestick
  • Can lead to chronic infection, cirrhosis, and hepatocellular carcinoma
  • Common in high-prevalence areas through perinatal transmission
• Hepatitis C is chronic
  • A bloodborne pathogen, there is no vaccine, but can be cured through antivirals
  • Often asymptomatic initially, but can lead to chronic liver disease as a single-stranded RNA virus
• Hepatitis D is transmitted through direct contact
  • Requires co-infection with hepatitis B to replicate
• Hepatitis E is transmitted via the fecal-oral route
  • Acute, self-limiting, except in immunocompromised individuals or pregnant women
• Herpes simplex virus type 1 (HHV-1) usually spreads through oral contact and can cause cold sores or genital herpes
• Herpes simplex virus type 2 (HHV-2) usually spreads through sexual contact and causes genital herpes
• Varicella-zoster virus (HHV-3) causes chickenpox which results in blisters on the skin or mucus membranes
• Epstein-Barr virus (EBV) (HHV-4) causes infectious mononucleosis, may be linked to certain cancers
• Mononucleosis lies dormant in memory B cells
  • Nasopharyngeal cancer and oral hairy leukoplakia are linked to EBV
• Cytomegalovirus (HHV-5) causes serious infections in newborns and immunocompromised people
• Kaposi's sarcoma (HHV-8) is a cancer that causes soft tissue lesions and is HIV-associated
• Human papilloma virus (HPV) 2, 4 causes common warts
• Human papilloma virus (HPV) 6, 11 causes genital warts
• Human papilloma virus (HPV) 16, 18 causes proliferative verrucous leukoplakia and cervical carcinoma

Fungi

• Pseudomembranous candidiasis manifests as wipeable white plaques in the oral cavity
• C. albicans defends against the body’s immune response by forming pseudohyphae
• C. albicans is the causative agent of median rhomboid glossitis and is a common opportunistic infection seen during chemotherapy
• Aspergillus sp. is the second most common fungus in the oral cavity
• Aspergillus sp. manifests as a black or yellow necrotic ulcerative lesion on the palate or posterior tongue