microbiology of perio disease

Question 1

What do gram bacteria look like?

Answer 1

Gram positive- dark purple (retains stain)- fixed cell wall (peptidoglycan) and one membrane, lipoteichoic acids which anchor in membrane
Gram negative- pink, 2 membranes + layer of peptidoglycan inbetween, polysaccharide (O antigens)

Question 2

What is subgingival plaque?

Answer 2

Predominantly gram positive layer
Overlying layers- gram negative anaerobes and motile bacteria
Close, mixed communities

Question 3

What is disease progression like?

Answer 3

Sporadic and often site specific

Question 4

What changes a quiescent site to an active one?

Answer 4

Change in host-immune status, age, environment

Change in microbial challenges
~type/no/virulence of organisms

Question 5

How are microbes established in sub gingival plaque?

Answer 5

1. Culture (til late 90s)
2. Sequencing 16s rRNA PCR clone libraries/hybridisation arrays- well conserved due to essential function, acts as molecular clock and species signature as elvolves slowly over time, PCR amplifies regions, primers contain sequencing adaptors and sample specific barcodes
3. Mass sequencing of 16s RNA amplicons

Question 6

What are red complex pathogens?

Answer 6

Eg. T. forsythia
Anaerobe
Unusual structure
2 membranes, peptidoglycan layer and surface layer, tfsAB, covered in glycans to avoid immune response and responsible for adhesion
Produces enzymes to human matrix cells (fibronectin binding protein, bspA)
Protease/toxin- prtH/cct
Glycosidases/ degrade host glycoproteins (release sugars)

Question 7

What is the role of glycosidases-sialidase?

Answer 7

Gain energy and change immune response
Harvest other bacterial glycans

Sialidase inhibitor, Tamiflu (oseltamivir) reduces plaque formation in lab

Question 8

What is P. gingivalis?

Answer 8

Black pigmented anaerobe
Well studied
Porphyrin on surface
LPS- endotoxin
Peptidoglycan capsule
Produce gingipains, rgp/kgp 
Sticky proteins on surface- fimbriae/pili
Immune evasion
Surface proteins- beta barrel

Question 9

What is the keystone hypothesis?

Answer 9

P. gingivalis shifts the whole population from non pathogenic to pathogenic even though it’s only present in low numbers (0.1%)

One pathogen causes a dysbiosis of a community

Targeted therapy?

Question 10

How does one pathogen cause dysbiosis?

Answer 10

Extracellular proteases- phospolipases and glycodidases

LPS endotoxin evades immune system

S-layer

Pili/fimbriae adhere to matrix proteins- fibronectin

Peptidoglycan capsule

Toxins- subvert phagocytic mechanisms/damage tissue eg. Leukotoxin

By products- putrescine, butyric acid, H2S

Question 11

What is necrotising ulcerative gingivitis?

Answer 11

Tissue invasion
Depression of host defences by smoking/stress
Depression of peripheral blood supply to tips of papillae
Selection of specific bacteria by host derived nutrients

Fuso-spirochaetal complex