Oral Ecology 1 Flashcards
What is oral ecology?
The study of all the relationships between microorganisms and the mouth (their environment)
What is the oral microbiome?
Multi-species community of microbes in the oral cavity
What 2 things can the environment impact in terms of microorganisms?
- Type of microorganism present
2. Number of microorganism present
Name an advantage of using a culture to determine microbial composition of the oral ecosystem
Cultivated bacteria can be used for metabolic studies and antimicrobial sensitivity tests
Name 4 disadvantages of using a culture to determine microbial composition of the oral ecosystem
- Only 50% of bacteria can be grown
- Biased towards predominant organisms
- Slow
- Labour intensive
Name 2 advantages of using a molecular sample to determine microbial composition of the oral ecosystem
- Relatively little bias
2. Rapid
Name 3 disadvantages of using a molecular sample to determine microbial composition of the oral ecosystem
- Properties have to be inferred from sequence data
- Limited data available
- Antimicrobial sensitivity testing not possible
Name 3 types of bacteria present in the mouth
- Indigenous species
- Supplemental species
- Transient flora
What disease is porphyromonas gingivalis associated with?
Periodontal disease
What disease is streptococcus mutans associated with?
Dental caries
What is characteristic of indigenous species of bacteria in the mouth?
Present in stable relationship with host and do not compromise the survival of the host
What is characteristic of supplemental species of bacteria in the mouth?
Present in small numbers but if environment changes their numbers can increase
Give 2 examples of supplemental species
- Streptococcus mutans
2. Porphyromonas gingivalis
What is characteristic of transient flora in the mouth?
Pass through the mouth but do not become established
Give an example of transient flora
E. coli
Name 2 beneficial effects of normal flora
- Colonisation resistance to more virulent bacteria
2. May release some nutrients from food (more important in animals e.g. cattle)
Explain 4 general mechanisms of disruption of the normal flora
- Suppression by antimicrobial agents
- Changes in general health or immunological status
- Hormonal changes e.g. pregnancy
- Local trauma
Explain 5 oral cavtiy specific mechanisms of disruption of the normal flora
- Changes in diet
- Reduction in salivary secretion
- Dental disease
- Dental treatment
- Changes in oral hygiene regime
What are 5 characteristics of the habitat provided for microorganisms by lips, cheeks and palate?
- Biomass restricted by desquamation
- Surfaces may have specialized host cell types
- Saliva has major influence
- Microflora has low diversity
- Facultative anaerobes present
What are 4 characteristics of the habitat provided for microorganisms by tongue?
- Biomass restricted by desquamation
- Highly papillated
- Acts as reservoir for obligate anaerobes
- Diverse microflora
What are 2 characteristics of the habitat provided for microorganisms by teeth?
- Non-shedding surface allows large masses of microbes to accumulate
- Distinct surface support distinct microflora due to intrinsic biological properties e.g. fissure, smooth surfaces, gingival crevice etc
- Host many anaerobes
Where in the oral cavity is the only non-epithelial covered surface in the body?
Junction between teeth and gum
Name the main microorganism found on the lips, cheeks and palate
Streptococcus
Name 5 microorganisms found on the tongue
- Streptococcus
- Actinomyces
- Rothia
- Neisseria
- Some gram negative anaerobes
Name 6 microorganisms found on the teeth
- Streptococcus
- Actinomyces
- Veillonella
- Fusobacterium
- Prevotella
- Treponema
What does the acquisition of resident oral microflora involve?
Interaction between adhesins on microbial cell surface and receptors on the host surface
What is the function of desquamation?
Ensure microbial load is light on mucosal surfaces
What forms an acquired pellicle on the teeth?
A wide range of receptors mainly from salivary proteins are absorbed onto the teeth
What is the function of an acquired pellicle on the teeth?
Increases potential for diversity in terms of microbial colonisation
What are accumulations of microorganisms on the teeth termed?
Dental plaque
What is a biofilm?
The term used to describe communities of microorganisms attached to a surface
What is an important feature of a biofilm?
Microbial cells with different metabolic requirements can exist successfully in these communities
Name 4 key advantages of biofilms to microbes
- Survival and protection
- Assists adhesion
- Extends habitat range
- Increases resistance to antibiotics / antimicrobial agents
Why does a biofilm aid adhesion?
Microorganisms which become attached may express receptors which allow other microorganisms to attach
Why does a biofilm extend habitat range for microorganisms?
Microorganisms tend to work together i.e. aerobes colonize, then facultative anaerobes enter and when oxygen used up, obligative anaerobes enter
How are microorganisms in a biofilm organised?
Spatially organised into a 3D structure, enclosed in a matrix of extracellular polymeric substance (EPS) such as long chain polysaccharides
Name an example of a long chain polysaccharide used in biofilms
Glucan
Name 2 functions of glucan in biofilms, other than being the EPS
- Aids bacterial adhesion
2. Acts as source of carbon when dietary supplies are limited
Why do biofilms have open structures?
Allows them to contain channels which facilitate the passage of nutrients and sometimes oxygen
Name 5 differences between planktonic microorganisms and biofilm organisms
- Freely suspended
- Can be single or multi-species but very large distances between cells
- No spatial organisation, although there can be some co-aggregation
- Limited cell to cell communication
- No protection from antimicrobials so immune system can easily remove cells
(All with respect to planktonic cells)
Name the 5 stages of development of a biofilm
- Initial attachment
- Irreversible attachment
- Maturation I
- Maturation II
- Dispersion
What occurs during stage 5 of biofilm development?
Climax community and optimal size is reached so external organisms become planktonic, leave to colonise elsewhere, become quiescent or die
How is initial attachment achieved during the formation of a biofilm?
Weak attraction and binding by non-specific forces (Van der Waals / Ionic) to the surface
How is irreversible attachment achieved during the formation of a biofilm?
Stronger, ligand-receptor binding to the surface
What 4 things can mediate irreversible attachment of a biofilm?
- Adhesins
- Surface fibrils
- Pili
- Flagellae
How is maturation I achieved during the formation of a biofilm?
Establishment of microcolonies and recruitment of additional microorganisms
How is maturation II achieved during the formation of a biofilm?
Growth of biofilm microcolonies by recruitment of additional microorganisms
In what 3 ways can microorganisms be recruited from during both maturation phases of biofilm development?
- Environment
- Multiplication from within
- Production of EPS (only maturation II)
Name 5 ways biofilms are more resistant to antimicrobial therapy
- Reduce penetration of antimicrobials
- Multi-drug efflux pumps can sequester drugs
- Reduced metabolic activity of microorganisms
- Resistant cells can remain viable so re-establish biofilm post treatment
- Natural resistance e.g. mutations and stress responses
What are the 3 basic steps in dental plaque formation?
- Clean tooth surface
- Salivary glycoprotein coat (pellicle)
- Bacterial colonisation
What disease is supragingival plaque associated with?
Dental caries
What disease is subgingival plaque associated with?
Periodontal disease
What is the main bacteria which predominate the initial formation of plaque?
Gram positive cocci, in particular streptococcus oralis
How is the dental pellicle formed?
Selective absorption of negative charged salivary glycoproteins preventing the continuous deposition of calcium phosphate
What is the main role of the pellicle?
Protect the enamel against abrasion and attrition and also serving as a diffusion barrier
How long does it take for dental plaque to become fully mature?
2 weeks
Once plaque thickens, what microorganism begins to dominate?
Actinomyces
What microorganism tends to increase as the plaque becomes more subgingival?
Veillonella
What occurs when dental plaque becomes calcified?
It becomes calculus
Where are the 2 most common locations in the mouth of calculus to be found?
- Lingual surfaces of lower anterior teeth
2. Buccal surfaces of upper first molars
