Periodontal pathogens

Question 1

What are the evidence that micro- organisms are important in the disease process?

Answer 1

• GCF becomes more prevalent in gingivitis and periodontal disease as it tries to wash away unattached bacteria
• Human studies show that 10-20 days of accumulated plaque induces inflammation
• When germ free animals were infected with bacteria from human periodontal pockets such as Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans, an inflammatory response was induced
• Virulence factors contribute to the pathogenesis of the bacteria implicated in periodontal disease

Question 2

What are the characteristics of pathogens involved in the disease process? What is the “key-stone” pathogen?

Answer 2

• Gingivitis: microflora is more diverse than in health, shifting from Streptococci to actinomyces, capnophilic and obligate anaerobic gram -ve
• Chronic periodontitis: motile, obligate anaerboic, asaccharolytic gram -ve rods. There is high proteolytic activity in GCF. Deeper pockets are filled with P gingivalis, T forsythia, T denticola. However, most bacteria are unculturable
• P gingivalis: the keystone pathogen

Question 3

What are the main organisms implicated in the disease process?

Answer 3

• P gingivalis in small numbers can cause a profound shift in microflra from symbiosis to dysbiosis, with an increase in the total number of bacteria. P gingivalis is an obligate anaerobe, gram -ve, rod that has a black pigment on blood agar
• Aggregatibacter actinomycetemcomitans is responsible for aggressive periodontitis. It is a facultative anaerobe, non motile, gram -ve rod. Its virulence factors include toxins (leukotoxins), LPS, capsule like polysaccharides, collagenases/ proteases

Question 4

What are 5 examples of virulence mechansims employed by periodontal pathogens?

Answer 4

Fimbrae

Gingipains

LPS

Volatile fatty acids

Stealing iron and porphyrin

Question 5

Explain fimbrae as a virulence mechanism

Answer 5

• Hair-like projections from bacterial surface for adherence

2 types:
Major fimbriae: 
• Long fillaments covering whole cell
• Promotes bacteria- host adhesion
• induce macrophages and neutrophils to produce several proinflammatory cytokines to promote 
Inflammation

Minor fimbriae:
• thin, short, secondary fimbrial structure
• responsible for bacteria-bacteria adhesion
also induces pro-inflammatory cytokines

Question 6

Explain gingipains as a virulence mechanism

Answer 6

• They are endoproteases unique to P. gingivalis

* Important for breakdown of protein substrates for food

Question 7

Explain LPS as a virulence mechanism

Answer 7

• Outer leaflet of outer membrane in Gram negative bacteria
• O-antigen or O-polysaccharide is most immunogenic part
• Lipid A is responsible for toxic effects: cell lysis, fever (pyrogen), septic shock

Question 8

Explain volatile fatty acids as a virulence mechanism

Answer 8

• Short organic acids (less than 6 carbons)
• Produced by anaerobic fermentation
• Inhibit T- and B- cell proliferation & production of IL-2, IL-4, IL-5, IL-6, and IL-10 from activated T cells

Question 9

Explain stealing iron and porphyrin as a virulence mechanism

Answer 9

• Iron & porphyrin is essential for growth of P. gingivalis.
• Major source of iron & porphyrin from host is haem in haemoglobin from red blood cells