Fermentable Carbohydrates, Extracellular polysaccharides and Sugar substitutes (Oral microbiology)

Question 1

Describe properties of cariogenic bacteria

Answer 1

• Acidogenic (acid-producing)
• Aciduric (acid-tolerant)
• Attachment mechanism to smooth tooth surface
• Ability to produce plaque polysaccharides (i.e. glucans)

Question 2

Describe sucrose metabolism:

Answer 2

• Streptococcus mutans and lactobacilli metabolize sucrose to glucans
• Glucosyltransferase (Gtf) -> Enzyme for glucan synthesis:
  1) GtfB -> Forms insoluble, structurally rigid matrix for S. mutans colonies
  2) GtfC -> In pellicle and form glucans when exposed to sucrose
  3) GtfD -> Soluble glucans that are primers for GtfB
• Glucans are responsible for bulk of plaque
• Sucrose has high energy glucose-fructose bond: allows glucan synthesis with no energy source

Question 3

Describe sugar uptake:

Answer 3

1) Permease -> Optimal when excess sugar, low pH, and high growth rate
2) Phosphoenol Pyruvate-phosphotransferase system (PEP-PTS) -> Optimal when sugars limited, neutral pH, and slow growth rate
3) Multiple sugar metabolism -> Breakdown of extracellular polysaccharides (biofilm) when monosaccharides are negligible

Question 4

Describe metabolism:

Answer 4

• s. mutans do NOT have the TCA cycle so stay in the anaerobic pathway
• Glycolysis creates lactic acid -> lower pH

Question 5

Describe cariogenicity of S. mutans

Answer 5

S. mutans are present predominately at the beginning of carious lesion formation.

• Metabolize sugars
• Forms insoluble extracellular glucans
• Produce acid
• Acid tolerant themselves

Question 6

Describe metabolic strategies for acid tolerance of S. mutans and lactobacilli:

Answer 6

• Transmembrane pH gradient -> ATPase pumps protons out of cell to maintain optimum intracellular pH
• Arginine deiminase -> produces ammonia (basic)
• Breakdown of urea by urease -> prevent pH lowering in immediate environment (NOT USED BY S. MUTANS)
• Stickland reaction -> Proline ring accepts two protons; profile common AA in plaque

Question 7

Describe properties of lactobacilli

Answer 7

• Only present after caries has developed (Advanced lesion)
• Acidogenic
• Acid tolerant

Question 8

Describe sugar substitutes

Answer 8

• Xylitol -> Competitively inhibits glycolysis to reduce acid production and growth; cooling effect when dissolved (takes energy)
• Arginine -> Metabolized by bacteria to produce ammonia-like substances, leading to increase in pH