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MICROBES IN ORAL DISEASE

Pathogenic Microorganism – Microorganism which is capable of causing disease.

Opportunistic Microorganism– Microorganism which is only to cause disease in compromised individuals when their defenses are weak, as the microbes will take opportunity by the reduced host defense.– These opportunists are frequently members of the body’s normal flora.

Virulence– Is a quantitative measure of pathogenicity.– Is related to an organism’s toxigenic potential & invasiveness.

Bacterial Virulence Factors – what the bacteria has to cause it to be pathogenic.

Bacterial Pathogenic Properties – how the bacteria use virulence factors to cause disease.

Bacterial Virulence Factors Bacterial Pathogenic Properties

1. Pili / Frimbriae 1. Adherence2. Glycocalyx (Slim Layer/Extracellular Polysaccharide)

2. Antiphagocyte Factor

3. Capsules 3. Tissue Damage4. Enzymes5. Toxins6. Haemolysins

BACTERIAL VIRULENCE FACTORS

1. Pili / Frimbriae Pili/ Frimbriae are fine, hair like filaments, extended from the cell surface. Pili, found mainly on G/-ve bacteria.

2. Glycocalyx (Slim Layer/Extracellular Polysaccharide) Surrounds and covers the outer surfaces of many bacteria. Allows the bacteria to adhere firmly to various structures,

eg. Oral mucosa, teeth. Made up of glycoprotein, water. Protect from dehydration and loss of nutrients.

3. Capsules

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A gelatinous layer. Surrounds the entire bacterial cell wall. Importance:

Protect the cell from the hazards of the environment. Hinders & inhibits phagocytosis (anti-phagocytic factor). Can be used an antigens in certain vaccines because they elicit protective antibodies. Mediates the adhesion of bacteria to human tissues.

(a prerequisite for colonization & infection).

4. Enzymes Several enzymes are produced by various bacteria that extracellularly & are associated with

invasiveness. 3 types:

i. Collagenase An enzyme that hydrolyses collagen & destroys collages fibres, thus allowing

bacteria to spread through the tissue more easily. Is produced by bacteria associated with periodontal disease ( Porphyromonas

gingivalis, Actinobacillus actinomycetemcomitans)ii. Hyaluronidase

Act as a ‘spreading factor’ by breaking down hyaluronic acid, a polysaccharide in the ground substance of connective tissue.

Is formed by many organisms including Streptococci.iii. Streptokinase

Causes the breakdown of the fibrin clots and thus aid the bacteria in the spread of infection.

Is formed by Streptococci.

5. Toxinsi. Endotoxin (only produced by G/-ve bacteria)

Stable at high temperature. Is responsible for many features of disease. Eg. Porphynumonas gingivalis – produces endotoxin that could cause tissue

destruction.ii. Exotoxin (produced by both G/+ve & G/-ve bacteria)

Toxins released extracellularly as the organism grows are called exotoxin. These toxins may travel from a focus of infection to distant parts of the body.

Hence, it causes damage in region far away from the site of microbial growth.

* G/-ve bacteria – Lipopolysaccharide is embedded in the outer membrane. – Lipopolysaccharide detaches from outer membrane and become endotoxin.*G/+ve bacteria – no outer membrane.

6. Haemolysins

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Proteins that are able to act on the animal / host cell membrane, causing cell lysis.i Lecithinases or Phospholipases:

Attack the membrane phospholipids of the host cell membrane and thus destroy the cell membrane.

ii Streptolysin O: Produced by Streptococci. Affects the sterols of the host cell membrane.

iii Leukocidins: Produced by A. actinomycetemcomitans (periodontopathic bacterium) and various

G/-ve bacteria. Lyse white blood cells, hence decrease host resistance.

Bacterial Pathogenic Properties

1. Adherence The initial adherence is specific, involving adhesion on the bacterial surfaces having

matching receptors on the host tissue. The major adherence contributing factors:

a) Pili/Fimbriaeb) Glycocalyx ( slim layer)c) Capsules

2. Antiphagocyte Factor In bacteria the major antiphagocytic factor is the bacterial capsule. Bacterial capsule can prevent in some ways the adherence of the phagocytes to the bacterial

cell surface. The major antiphagocytic contributing factors:

a) Capsuleb) Pili/Fimbriae

3. Tissue Damage The major tissue damage contributing factors:

a) Enzymesb) Bacterial toxinsc) Haemolysins

* For essay question, each factor should be elaborated.*

Microorganisms in Oral Disease

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1. Dental caries The main cariogenic bacteria : Streptococcus mutans ( Acidogenic & Aciduric )

* Acidogenic – able to produce acid ** Aciduric – able to live in acidic environment *

2. Periodontal disease The main periodontopathic (periodontopathogenic) bacteria :

Porphyromonas gingivalis ( Asaccharolytic)