STREPTOCOCCUS MUTANS

Dr. Ali YaldrumFaculty of Dentistry, SEGi University.

LEARNING OBJECTIVES

At the end of this session, the student should be able to:

1.Describe what are Streptococci Organisms

2.Classification of Streptococci Organisms

3.Describe role played by Streptococcus mutans in health and disease

1. GENERAL PROPERTIES

• Catalase negative

• Gram +ve

• Spherical or Oval Cocci

• Appears in pairs or chains

• 0.7 to 0.9 um in diameter

• causes a wide variety of diseases (fig. 1)

2. PATHOGENICITY

Pathogenic Streptococcus produces several extra cellular substances that contribute to their pathogenicity

2. PATHOGENICITY

1. products that destroy the phagocytic cells & ingest them

2. produces enzymes that digest the connective tissue resulting in extensive tissue destruction

3. can also lyse “Fibrin”

caries

pneumonia endocarditis

necrotizing fasciitismeningitis(see f ig 2&3)

(f ig 1)

facial cel lulitis which progressed relentlessly with necrosis(fig 2)

(f ig 3)

4. CULTURE

• Grow well on blood agar

• There are 3 types of hemolytic reactions produced on blood agar (fig 4 & 5)

1.α -hemolysis

2.β-hemolysis

3.γ-hemolysis

T YP ES OF HEMOLY T IC REAC T IONS(F IG 4)

β-hemolysiswide clear translucent zone

of complete hemolysis around the colony

α -hemolysisnarrow zone of partial

hemolysis

γ-hemolysis: no hemolysis occurs

T YP ES OF HEMOLY T IC REAC T IONS(F IG 5)

shorter arrow: α hemolysis longer arrow: β-hemolysis

3. SEROLOGY

• Surface Carbohydrate antigens are related to their virulence

• Hence serogrouping termed Lancefield grouping is useful in identification of the more virulent β-hemolytic species

• 20 Lancefield groups are recognized

MUTANS GROUP

• originally isolated from human teeth by Clark in 1924

• in 1960 caries were induced experimentally in animals, artificially infected with strains resembling S.mutans

• cells can loose their coccal morphology and appear as cocco-bacilli

• 9 serotypes have been identified (a-h & k)

• Human isolates are : c,e f and k

• S.mutans have been implicated as the primary pathogen in :

1.enamel caries in children & young adults

2.root surface caries in elderly

• occupy hard non-shedding surfaces i.e teeth or dentures

• Regularly isolated from dental plaque at carious site, but low prevalence on sound enamel

• opportunistic pathogens (isolated from cases of infective endocarditis)

• communicate with other mutans

• cell wall carbohydrate antigen (I/II)

• lipoteichoic acid

• lipoproteins

• cell wall associated protein

Streptococcus mutans

Extracel lular Polysaccharides (glucan, mutan, fructan)

Intracel lular Polysaccharides (glucan, mutan, fructan)

excess sugar

glucosyl and fructosyltransferase

contribute to characteristic colonial morphology

act as carbohydrate reserve, used to produceacid in absence of available sugar

Salivarius group

This group consists of two bacterias

1. S. salivarius

2. S. vestibularis

• salivarius prefer mucosal surface especially the tongue

• produce unusual quantity of extracellular fructan

• rarely isolated from diseased sites

• S. vestibularis prefers the vestibular mucosa

• no extracellular polysaccharide production

• produces ‘urease’ leading to rise in local pH and hydrogen peroxide

Anginosus group

The group is differentiated into

• S. constellatus

• S. intermedius

• S. anginosus

• readily isolated from dental plaque & from mucosal surface

• cause serious, purulent diseases

• commonly found in abscess of internal organs

• no strain produces polysaccharide from sucrose

Mitis group

This group consists of

• S. sanguinis

• S. gordonii

• S. mitis

• S. oralis

• Early colonizers of tooth

• produce soluble and insoluble glucans from sucrose

• contribute to plaque formation

• ammonia generation from arginine

• S. sanguinis produces a protease that can cleave sIgA

• S. gordonii can bind with salivary amylase enabling the breakdown of starch

1. Philip D. Marsh, Michael V Martin, “The Resident Oral Microflora” in Oral Microbiology, 5th Edition, Churchil Livingstone, 2009, pp 25-35

References