Acquisition of oral microflora

Question 1

What factors influence microbial colonisation of the oral cavity?

Answer 1

• Teeth erupting will cause new organisms to come in

* Species associated with perio disease can be detected in 18- month olds

Question 2

What factors may cause changes in the oral microbial composition over time?

Answer 2

• Pioneer species modifies local environment, provide conditions for colonisation by other species
• Change pH through metabolism
• Reduce O2 levels
• Modify existing receptors or expose new ones. When they bind and metabolise a host cell, the enzymes may degrade host proteins and expose new sites on the host for attachment by other bacteria
• They may make new nutrients when they metabolise. These can become new food sources for other bacteria which couldn’t otherwise survive
• Breakdown products like peptides and heamin which may kill other bacteria
• Shortage of nutrients due to competition

Question 3

What are the types of microbial succession?

Answer 3

Autogenic succession:
Changes within the community influences succession

Allogenic succession:
Changes outside the community influences succession

Question 4

List autogenic changes

Answer 4

• O2 consumption
• pH change
• Food chain
• Receptor exposure
• Inhibitory substances
Nutrient limitation

Question 5

List allogenic changes

Answer 5

• Tooth eruption
• Changes in tooth structure
• Denture wearing
• Antimicrobial agents
• Changes in immune response
Oral hygiene

Question 6

List the advantages & disadvantages of life within a biofilm

Answer 6

Advantages
• Storage of food via extracellular polysaccharides
• Lower O2 to allow anaerobe growth
• Cohesion
• Quorum sensing: way bacteria communicate via chemical release which can stimulate a coordination in morphological changes to survive changes
• Enzyme complementation: sharing of enzymatic function between different species
• Horizontal gene transfer: cell-cell proximity allows for transfer of DNA eg. acquisition of antibiotic resistance genes, virulence genes, etc
• Resistance to antimicrobial substances for example inhibiting diffusion
• Resistance to host immune system eg. cannot be phagocytosed, shielded from antibody recognition, protection from other arms of innate & acquired immunity

Disadvantages
• Bacteriocins: toxins produced by bacteria to kill other bacteria
• Hydrogen peroxide: radicals
• Organic acids 
• Nutrient competition