Topic 45-Oral Microflora and Dental Plaque

What guides the transition from planktonic to biofilm state?

changes in gene expression and EPS production

protein of whole adult tooth is primarily

collagen

Gingiva (gums) form a

collar around each tooth and includes gingival sulcus (sub gingival crevice) junctional epithelium

streptococci viridian's groups

colonize in mouth gram positive cocci facultative anaerobes (prefer aerobic) can ferment anerobically

Saccharomycetales

commensal yeast species proposed to be antagonists of opportunistic fungal pathogens

Human oral bacterial microbiome (salivary)

compromised of over 600 prevalent taxa at the species level, with distinct subsets predominating at different habitats 1. Streptococcus 2. Prevotella 3. Haemophilus/Neisseria/Veillonella

Fungi are generally not

considered to be beneficial contributors of the normal oral flora of a healthy mouth

dental plaque

dense bacterial mass (biofilm) tightly adherent to the tooth surface

The oral cavity has unique physiological features that play a role in

development and site specific characteristics of oral plaque aka ecology of biofilm communities

In 1965, Jensen and Loe provided

didactic experimental proof of casual relationship between dental plaque and gingivitis

dental plaque/biofilm formation involves

direct cell to cell adhesion via specific surface determinants

S. sanguinis

dominant colonizer of the tooth and supragingival plaque in health, coincide with eruption of teeth

three layers of the tooth

enamel dentine cementum

demineralization

erosion and release of calcium phosphate ions under acid conditions (low pH)

Colonization with pathogen S. mutant coincide with

eruption of teeth

gingival sulcus

formed by the free gingiva, V-shaped shallow space around the tooth in the healthy periodontium

planktonic bacteria

free-living, single cell bacteria before they attach

microbial biofilm formation/growth (after cleaning)

generally shows species succession mediated by microbial metabolic needs and site-specific nutritional availability early colonizers in supragingival plaque late colonizers in subgingival plaque coaggreation is present

What increases numbers on malodorous (overgrowth) tongues?

gram-negative anaerobes

Teeth

hard tissue exposed to environment only mineralized enamel surfaces of teeth are exposed in healthy person

Below the gumline (sub gingival)

host tissue is main food source asaccharolytic; highly proteolytic; hemolytic bacteria tend to be: facultative anaerobes obligate anaerobes commonly colonized by G- anaerobic bacilli and spirochetes, but at very low numbers in healthy person

S. salivarius

largest proportion of the total oral microflora due to being dominate colonizer of the mucosa in health

secondary colonizers

mostly gram negative bacilli (Capnocytophaga ochracea) bind to primary colonizers cared for mouth has sparse plaque

mucosal primary colonizers

mother to infant transmission before teeth eruption Ex: S. mitis/S. salivarius

Subgingiva is also typically colonized by very low numbers of

obligate anaerobes Ex: Porphyromonas, Prevotella, Fusobacterium, Veillonella species

species specific required nutrients

often provided through the waste/by-products of other microbial species in the biofilm (plaque) community use each other for sources and are usually closer together

AEP is

overall negatively charged due to immediate deposition of soluble salivary organic components (glycoproteins) that repel bacterial adhesion to clean teeth under optimal oral pH conditions

Above the gumline (supragingival)

oxygen availability higher nutrients from host diet higher nutrients from host tissue lower bacteria tend to be: aerobic, facultative anaerobes, capnophilic (CO2 growth dependent bacteria) saccharolytic bacteria

what occurs after tooth eruption?

permanent colonization of streptococci climax communities

biofilm

permanently attached (non-motile) polymicrobial communities (dental plaque) embedded in the extracellular polymeric substances (EPS)

endogenous (commensal) microorganisms found in the oral cavity are

predominantly members of the Streptococci genus in a healthy mouth

In 1972, Loe provided

proof of the casual relationship between presence of dental plaque and dental caries via demonstrating the efficacy of oral antiseptics (chlorhexidine)

Chronic human viral infections is a

risk factor for bacterial infections

Acquired enamel pellicle (AEP)

salivary coating on the tooth surface made up of organic molecules (glycoproteins) 1. provides lubrication 2. provides a barrier to tooth erosion caused by acidic molecules generated from fermenting oral bacteria

EPS

self-secreted microbial biofilm matrix consisting of polysaccharides and other polymeric macromolecules that primarily function to protect and architecturally organize the microbial community

Calcium ions in AEP

soluble inorganic component of whole saliva that binds to salivary proteins can facilitate bacterial adhesion to the pellicle by forming a positively charged bridge (low pH)

what are key determinants for dental plaque?

species composition and accumulation

Specific bacterial species have

specific bacterial cell surface adhesion molecules that bind to specific protein receptors (ligands) found in the tooth pellicle and overcome that negative charge

junctional epithelium

starting from the base of the sulcus, is directly attached to the tooth surface

Oral streptococci are historically referred to as

streptococci viridians (group name) and include a wide variety of species commonly classified into taxonomic groups

Example of coaggreagation

streptococcus sanguinis cells (cocci) form "corn cobs" surrounding Corynebacterium matruchotii cells (bacilli)

What do oral bacteria need from host to grow? (diet and tissue)

sugars or protein

Saliva is

supersaturated with soluble calcium phosphate (1.5mM) at neutral pH that precipitates when pH increases

primary colonizers

supra gingival plaque population on tooth surfaces in a cared for mouth gram positive cocci (S. sanguinis, S. oralis, S. gordonii, S. mitis)

dentine

bone-like tissue (70% inorganic) covered by enamel at crown and cementum at root

What will help determine the preferred distribution of certain species within the oral cavity and their site specific metabolism?

1. relative amounts of oxygen available 2. microbial oxygen tolerance and/or requirements

mycobiome

101 genera identified (w/9-23 genera in any single person) Candida species were isolated from 75% of all study participants

Site specific microbial metabolism also depends on

amount of plaque build up

when does increased diverse colonization of the oral cavity occur around?

9 months to 1 year

periodontal pockets contain ____ O2

About 0.6-4%

posterior surface of the tongue contains ____ O2

About 12%

Normal air contains ____ O2

About 20%

6 taxonomic groups of streptococci viridians (SSMMAB)

anginosus group minis group sanguinis group mutans group salivarius group bovis group (gut microbes rarely in the oral cavity/endocarditis/colon cancer)

remineralization

calcium phosphate deposition and assimilation (high pH >7)

A bacterial factor that influences microbial adherence and persistence in the oral cavity is

EPS

anginosus group

S. anginosus S. constellatus S. intermedius (oral disease)

Bovis group

S. gallolyticus S. infantarius S. pasteurianus

Sanguinis group

S. gordonii S. sanguinis (typically found in mouth) S. parasanguinis S. oligofermentans

Mutans group

S. mutans (oral disease) S. sobrinus (oral disease)

mitis group

S. oralis S. mitis (typically found in mouth) S. cristus S. infantis

salivarius group

S. vestibular is S. salivarius (typically found in mouth)

calculus

accumulation of saliva and gingival fluid materials (calcium salts) that become mineralized on plaque/desquamated epithelial cells and adhere to tooth surfaces.

enamel

acellular, avascular, hard, brittle hardest tissue in the human body 96% inorganic matter 4% organic matter primarily made up of hydroxyapatite (crystalline calcium phosphate) Also, other ions from endogenous/exogenous sources like magnesium or fluoride

coaggreagation

between bacterial organisms of different species

autoaggregation

between bacterial organisms of same species

Viruses are

NOT considered beneficial contributors of the normal oral flora of the health mouth most viruses identified are bacteriophage

most associated with odor

Neisseria Veillonella Fusobacterium Porphyromonas Parvimonas Prevotella-produce volatile sulfur waste

tongue is predominantly colonized by

Streptococcus spp. S. salivarius other commensal isolates seen include porphyromas, prevotella, actinomyces, and veillonella species

late colonizers

bind to secondary colonizers gram negative obligate anaerobic bacilli and spirochetes reside in subgingiva prominent in periodontal disease development

cementum

thin bone-like tissue (55% inorganic) that fixes teeth to the alveolar (jaw) bone

oral colonization after birth is

transient aka NOT PERMANENT population will change

AEP initially repels, but

ultimately promotes bacterial adhesion

oral Mucosa

variety of soft tissue sites with unique characteristics

oral cavity of fetus is

virtually sterile (low load)

Bacteriophage in patients with periodontitis

were proposed to likely kill their bacterial hosts this contributing to good oral health

In an uncared for mouth, plaque accumulates

when certain secondary colonizers accumulate and dominate in the population teeth at higher risk for caries (S. mutant, lactobacillus fermented) or periodontal (gum) disease (prevotella and actinomyces)

materia alba

white or cream-colored cheesy mass that can collect over dental biofilm on unclean, neglected teeth; it is composed of food debris, mucin, and bacteria loose "white" accumulation of food, desquamated epithelial cells and other debris around teeth