Lecture 10: The oral cavity as a microbial habitat

Mucosal Surfaces (soft tissue)

lips, cheek, palate, tongue

Hard surfaces/ non-shedding surfaces (hard tissue)

teeth

Enamel

outer layer, hardest living tissue in the body

The structure is solid, but one crack makes it weak

pulp

supplies blood to the tooth

gum (gingiva)

help hold tooth

supra-gingival plaque

plaque above the gum

sub-gingival plaque

plaque below the gums

pits and fissures

hard to reach areas that house microbes

GCF (gingival crevicular fluid)

fluid that comes from gingival crevices derived from serum (blood)

whole saliva parts

resting saliva and stimulated saliva

resting saliva

saliva in the mouth normally

stimulated saliva

• gum, food, etc. makes you generate more saliva

• more liquid (more volume)

• more liquid = dilution

act as a buffer in saliva

sodium, potassium, calcium, magnesium, phosphate, bicarbonate

How temperature affects microbial growth

• 35-36°C

• Can increase to 39°C in periodontal pockets with inflammation

• changes can regulate gene expression in bacteria for genes encoding enzymes and fimbriae

• changes can make bacteria more virulent

how redox potential / anaerobiosis affects microbial growth

• oxygen tension on tongue varies from 12-16% and in buccal folds 0.3-0.4%

• oxygen content varies by location

• more oral organisms are facultative or obligate anaerobes

• early colonizers are more aerotolerant, late ones are more anaerobic

why early colonizers are more aaerotolerant

the first microbes come in and start using up the oxygen, therefore decreases oxygen in the environment and allows for anaerobic microbes to come in

how pH affects microbial growth in the oral cavity

• 6.75-7.25 variation between locations

  • palate 7.34, buccal mucosa 6.3

• regulated by saliva, due to the buffer created by the salts present in saliva

• varies in disease

  • healthy: 6.9, disease: 7.4+

basic environments (gums)

P. gingivalis likes to live here

consumption of sugar

lowers the pH because sugars ferment into acids, and acids lower pH

S. mutans love acidic pH and cause caries

endogenous

already present in the mouth

endogenous nutrients in the mouth

saliva: amino acids, peptides, proteins

GCF: albumin, protein

Bacterial products: carbohydrates, proteins, sugar, and fats)

exogenous (outside) nutrients in the mouth

food we eat: fermentable carbohydrates (lowers pH), metals

host defense

immune systems ability to fight infection

affects microbial growth in the mouth

host genetics

some people are more genetically prone to oral disease

affects microbial growth in the mouth

antimicrobial agents and inhibitors

antibiotics, toothpaste, and mouthwash kills good and bad bacteria as they are non specific

affects microbial growth in the mouth

neutropenic

less neutrophils, more prone to fungal infections

saliva flow

physically removes microorganisms everytime you swallow

mucin / agglutinins

physically removes microorganisms

Lysozyme-protease-anion

causes cell lysis

lactoferrin

iron sequestration-keeps iron low for bacteria (bacteria love iron)

apo-lactoferrin

causes cell killing

sialoperoxidase system

hypothiocyanite production (neutral pH)

hypocyanous acid production (low pH)

histatins (most antifungal protein)

anti fungal with some antibacterial activity

Defensins (a & b)

anti microbial & immonomodulatory activity

Cystatins, SLPI, & TIMP

cysteine, serine & metallo-protease inhibitors

Chitinase & chromogranin

anti fungal

Calthelicidin & Calprotectin

antimicrobial (AMPs- antimicrobial peptides)

intra-epithelial lymphocytes & langerhans cells

cellular barrier to penetrating bacteria and/or antigens

sIgA

prevents microbial adhesion and metabolism by neutralizes microorganism

IgG, IgA, IgM

prevent microbial adhesion; opsonins; complement activators

Complement

activates neutrophils

Neutrophils / macrophages

phagocytosis

how bacteria colonize the oral cavity

• adherence properties

• synergistic bacteria (bacteria that get along with existing bacteria)

• nutritional substrates (find nutrition)

• temperature and moisture

how bacteria are killed or expelled from the oral cavity

• swallow them right away

• agglutination

• antimicrobial properties of saliva

• mechanical shearing

• antagonistic bacteria (bacteria kills other bacteria)

antimicrobial agents

fluoride, chlorohexidine, antibiotics

biofilms

matrix-enclosed microbial accumulation that adhere to biological or non-biological surfaces

surface attachment

• first step in biofilm development

• free floating bacteria adhere to abiotic/biotic surface and become sessile

• reversible initially and becomes irreversible

microcolonies

• second step of biofilm development

• bacteria secrete extra polysaccharides (EPS)

• cell proliferation and coaggregation of the bacteria happens inside the EPS

macrocolonies

• third (final) step of biofilm development

• mushroom and tower like structures hold the bacteria inside

• at a certain point the biofilm cannot sustain all the bacteria, some bacteria leave to start a biofilm somewhere else

population growth dynamics in biofilm

as population grows, there is more transport limitation (limitation of nutrients, oxygen)

higher mass = higher limitations

cell fate of individuals dynamic in biofilm

the population increases, but individual cells start dying because of the nutrient limitations

cells in the core dynamic of biofilms

as the population grows, there comes a time where only the first layer are in contact with the base

quorum sensing

intercellular (between 2 cells) signaling as a regulatory mechanism that plays a significant role in coordinating various stages of biofilm formation

quorum sensing functions

• respond to population density (bacteria die and send signals for others to die)

• controls gene expression

• capable of auto-induction

• self-recognized secreted molecules called auto-inducers (mediators)

Peptide as a auto-inducer

Streptococcus mutans

fungal QS molecule as a autoinducer

famesol (candida produces)

plaque

dental biofilm - a complex microbial community on the surface of teeth

association

first step of dental plaque formation

bacteria associates with the teeth via van der waal forces and attaches to the pellicle in a reversible process

adhesion

second (final) step of dental plaque formation

when there is receptor mediated interaction, the adhesion becomes irreversible

salivary proteins and glycoproteins in acquired enamel pellicle

• sialic acid

• proline-rich proteins

• mucins

• agglutinin

• amylase

bacterial components of the acquired enamel pellicle

• glucan

• glucosyltransferases

bacteria and the tooth

bacteria rarely come in direct contact with the tooth enamel, they damage the surface by producing acids and sit on the pellicle

pellicle formation

initiates within seconds of any clean surface being introduced in the oral cavity, spontaneous and cannot be permanently removed

association

the least intimate form of surface interaction, weak and reversible attachment

adhesion

• a more intimate form of attachment than association

• stable, irreversible attachment

• surface components (adhesins) interacting with complementary molecules on the host surfaces

• interaction between bacterial adhesin and pellicle or cell receptor

invasion

penetration of the mucosal barrier by bacteria

coaggregation / coadhesion

• interbacterial interaction - initial layer of bacteria forms and other bacteria come and interact with it

• when 2 bacteria bind to eachother, they agglutinate and precipitate out of a solution

biofilm maturation

• metabolic interactions of one bacteria affect the other bacteria

• environment modifications

• gradients of oxygen and nutrients

• matrix

enzyme complementation (synergistic)

bacteria breaks a part of the something and another breaks a different part, they work together until it is fully broken down

food chains (synergistic)

bacteria produces food for other bacteria

coadhesion (synergistic)

bacteria binds to other bacteria

cell-cell signaling (synergistic)

sends signals to each other

gene tranfer (synergistic)

gene transfer

bacteriocins (antagonistic)

bacteria produce bacteriocins peptide antibodies to kill other bacteria

hydrogen peroxide (antagonistic)

bacteria produce it to kill other bacteria with oxidative stress

organic acids (antagonistic)

lower the pH, if other bacteria don’t like acidic environments they die

nutrient competition (antagonistic)

everybody needs to eat

microbial interaction in plaque

as dental plaque biofilm develops, local environment changes = microbial succession

synergistic and antagonistic effects