Normal Oral Microflora Microflora of Dental Caries Microflora of the Root Canal ( endo )Microflora of the Periodontal Pocket (perio) Oral Microbiology
The Importance of Studying BacterialPathogenesis• A human body has 1 X 1013 eukaryoticcells and 1 X 1014 bacterial cells• Microbial infections are the most epidemicdiseases and the leading cause of death– Diarrhea and enteric bacteria– Tuberculosis and Mycobacterium– Ulcer and Helicobacter infection– Urinary tract infection– STDHow microbiology is related to dentistry?
The first microbes observed: Anton Van Leeuwenhoek (1632-1723) Developed the microscope and was the first to discover oral bacterial flora: “I didn’t clean my teeth for three days and then took the material that had lodged in small amounts on the gums above my front teeth…. I found a few living animalcules..”
What causes dental caries?• Pre-microbiology era– Dental caries is the death (decay) of a tissue• Microbiology period era– Dental caries is a microbe related disease
Plaque is a complex microbial community
How to identify bacteria within dental plaque?• Culture methods take saliva or plaque, dilute and plate on appropriate plates, grow to single colonies, identify by microscopic and biochemical methods• 16S DNA/RNA based detection use 2 oligo-nucleotide primers universal to ALL bacteria 16S rDNA, PCR amplification of the total saliva or plaque DNA pool, clone the PCR product and sequence, phylogenetic analysis using computer database
Supragingival Plaque Predominant cultivable microflora obtained from occlusal fissures Specie Median percentage Range % isolation S.mutans 25 0-86 70 S. Sanguis 1 0-15 50 S. Oralis 0 0-13 30S. Anginosus 0 0-3 10A.Naeslundi 3 0-44 70 L. Casei 0 0-10 10L. plantarum 0 0-29 10
Subgingival plaque Bacteria Mean percentage Frequency %Streptococcus 23 100Actinomyces 42 100 Prevotella 8 93 Veilonella 14 93 S. Sanguis 6 86A. naeslandii 19 97
Current knowledge about bacteria in plaque• Both culture and DNA/RNA-based techniquesare used for identification and quantification oforal microorganisms• Overall, there are ~700 species exist in the oralcavity• ~20% of these 700 species have been cultivated• Both Gram-positive and Gram-negative exist• Some archaea are found• Most anaerobic or facultative anaerobicWho are the bad guys?
The first isolation of cariogenicbacteria by Clark, 1924Isolation of cariogenic bacteria fromcaries lesionsDiscovery of Mutans streptococci
Keyes and Fitzgerald, 1962’sRe-isolation of “Mutans streptococci”: • Streptococcus mutans (human) (same species Clark isolated in England in 1924) • Streptococcus sobrinus (human) • Streptococcus rattus (rats) • Streptococcus cricetus • Streptococcus ferus • Streptococcus macacae • Streptococcus downeii
• The “cariogenic bacteria” – bacteria associated with dental caries• Actinomyces – early colonizers and root caries • A. odontolyticus • A. naeslundii genospecies 2 • A. isrealii • A. gerensceriae• Lactobacilli (L. casei) – caries progression• Mutans streptococci (S. mutans) – caries initiation
The virulence factors of cariogenic bacteria1. Acid production (acidogenicity) • Lower the pH to below 5.5, the critical pH, drives the dissolution of calcium phosphate(hydroxyapatite) of the tooth enamel • Inhibit the growth of beneficial bacteria, promote the growth of aciduric bacteria. • Further lower the pH, promote progression of the carious lesion
2. Acid tolerance (aciduricity) – Allows the cariogenic bacteria to thrive under acidic conditions while other beneficial bacteria are inhibited. This results in dominance of the plaque by cariogenic bacteria
• Glucan formation – Allows the cariogenic bacteria to stick onto the teeth and form a biofilm – Glucan mediated biofilms are more resistant tomechanical removal – Bacteria in these biofilms are more resistant to antimicrobial treatments
Dental Caries Carbohydrate (Sucrose) Cariogenic bacteria such as strep. mutans Glucans/levans AcidsPlaque formation Demineralization
Dental caries is a bacterial infectious diseaseTransmission • Mother – Child (vertical transmission) -true for most oral bacteria • Persons in close contact to the baby • Horizontal transfer (between spouses) is rare, only observed in some periodontal pathogens (i.e. P.gingivalis) The most common vehicle is saliva
New problem: everybody has S. mutans!• So…….Why not every body who has S. mutans develop dental caries? S. mutans is not present in high portions Acid produced is neutralized by urea or ammonia produced by other bacteria in the plaque S. mutans is away from the tooth surface so acid produced is diffused
The ecologic plaque hypothesis Both pathogenic and commensal (nonharmful) bacteria exist in a natural plaque. At sound site, the pathogenic bacteria may exist in low numbers to cause any clinical effect, or they may exist in higher numbers, but the acid produced is neutralized by the action of other bacteria. Disease is a result of a shift in the balance of the residence microflora driven by a change in the local environment (frequent sugar intake etc).
Human genome project Oral bacteria genome projects Metagenomics of the oral cavity
Human genomeComplex genetic only hasmakeup of man 200,000 genesEach oral bacterium 2000 to 6000 genes.• With over 1000000 bactrial genes in the oral cavity
The dental plaque is a complex multispecies biofilm
Environment al Attachment Modification MicrobialTransmission pH, Eh & Growth of succession Colonization Pioneer Expose new G+, G- species receptors (periodontal Generate pathogens new nutrients Pioneer colonizers: S. oralis Mother to S. mitis Child S. salivarius Increased Climax species S. sanguis community S. anginosus diversity S. gordonii