L1 Commensal Oral Microflora

Question 1

What are the 5 types of microorganism present in the oral cavity?

Answer 1

• Bacteria: predominant microorganism
• Fungi
• Mycoplasma (prokaryotic cells with no cell wall)
• Protozoa
• Viruses

Question 2

Name some oral sampling methods.

Answer 2

• Collection of saliva
• Concentrated oral rinse: patient rinses mouth with saline and this sample is then sent to lab
• Swab: e.g. charcoal swap
• Imprint cultures: foam sponge placed on lesion, then placed on agar plate
• Biopsy and smears

Question 3

Name some identification methods.

Answer 3

• Biochemical tests
• Staining
• Cell morphology
• Molecular approaches e.g. sequencing nucleic acids
• Selective/differential media on agar plate

Question 4

What is meant by the normal microflora?

Answer 4

The microorganisms which colonise the oral cavity, skin, GI tract, upper respiratory tract and parts of the genitourinary tract.
Colonisation is generally neutral or beneficial.

Question 5

What are the advantages of normal microflora?

Answer 5

• Lactobacilli, streptococci and enteric bacteria synthesise and excrete vitamins
• Prevents colonisation by pathogens
• Stimulates development of lymphatic tissue
• Stimulates production of cross-reactive antibodies

Question 6

What are the disadvantages of normal microflora?

Answer 6

• Nutrient competition with the host
• Low grade toxaemia: bacteria entering bloodstream and affecting immune system
• Endogenous infection e.g. patients on antibiotics susceptible to Candida
• Synergy with pathogens, can promote growth of pathogens

Question 7

What is meant by the term opportunistic pathogens?

Answer 7

Opportunistic pathogens: commensal microorganisms that cause infection under certain conditions e.g. commensal microorganisms moving from one area to another

Question 8

What determines if a pathogen is commensal or opportunistic?

Answer 8

Interplay of microbial and host factors.

E.g. caries development depends on diet, saliva flow and dental plaque microbes

Question 9

Describe the oral microflora at birth.

Answer 9

• Oral cavity is sterile

- Then streptococcus species become present (thought to be due to feeding)

Question 10

Describe the oral microflora at 1 year.

Answer 10

Soft tissue colonisers are present:

• Streptococci
• Staphylococci
• Neisseria
• Viellonella
• Actinomyces
• Lactobacilli

Question 11

Describe the oral microflora after tooth eruption.

Answer 11

Microorganisms favouring hard tissue become present:

• S.mutans
• S.sanguis

Question 12

Describe the oral microflora after teeth are lost.

Answer 12

• A 2nd childhood microflora is present in older people who lose teeth
• They may then get a prosthetic appliance e.g. denture- another type of plaque similar to enamel plaque forms- may harbour large numbers of yeast, particularly on the acrylic of the denture

Question 13

Describe the microflora of crevicular tissues.

Answer 13

• Predominantly anaerobic organisms present e.g. Prevotella spp

Question 14

Describe how microflora differ in different locations of the oral cavity.

Answer 14

• Dorsum of tongue: highly colonised by anaerobic bacteria around papillae
• Buccal mucosa: sparsely colonised, more opportunistic pathogens found here
• Tooth surface: supra and sub gingival plaque colonies differ
• Gingival crevice: anaerobic organisms which can cause periodontal infection
• Prosthodontic/orthodontic appliances: organisms attach to artificial surfaces that may outcompete our own microflora

Question 15

What microbial factors affect the oral ecosystem and species present?

Answer 15

• Competition for adherence sites
• Some species help other species to adhere
• Nutrient competition
• Bacteriocins can be released to inhibit growth of microorganisms

Question 16

Describe gram negative bacteria.

Answer 16

• Thin peptidoglycan layer

- Stain pink/red

Question 17

Describe gram positive bacteria.

Answer 17

• Extremely thick peptidoglycan layer

- Stain purple/blue

Question 18

What percentage of the bacteria in the oral cavity are unculturable and unidentified?

Answer 18

> 40%

Question 19

How many species have been isolated from dental plaque?

Answer 19

> 300 species

Question 20

Describe the microflora of clinically healthy gingiva.

Answer 20

Mostly aerobic and facultative anaerboic bacteria (can grow in presence or absence of oxygen)

Question 21

Where are the following species most commonly found: S.salivarius, S.mutans?

Answer 21

• Streptococcus salivarius: tongue

- Streptococcus mutans: teeth (hard tissues)

Question 22

Name some cariogenic bacteria.

Answer 22

• S.mutans
• S.sanguis
• S.mitior
• S.salivarius
• L.casei
• Actinomyces viscosus

Question 23

Name some bacteria found in periodontal disease.

Answer 23

• P.gingivalis
• P.intermedia
• Eubacterium
• Fusobacterium
• Peptostreps

Question 24

What are mycoplasma?

Answer 24

A genus of bacteria with no cell walls.
Smallest prokaryotes to be grown on bacteriological media.
Form unusual shapes, fluid in growth.

Question 25

Are mycoplasma found in the oral cavity?

Answer 25

• Up to a third of people have mycoplasma in their oral cavity
• E.g. M.orale, M.salivarium, M.buccale

Question 26

Where are mycoplasma relevant?

Answer 26

• M.salivarium is strongly associated with periodontal disease
• M.orale can cause infections in leukemic or immunosuppressed patients
• M.buccale, M.faucium and M.lipophilum are implicated in diseases of the gingival crevices and respiratory tract

Question 27

What are protozoa and where are they found in the oral cavity?

Answer 27

Single celled eukaryotes.

• Entamoeba gingivalis: anaerobe found in gingival crevice, possible association with chronic periodontitis. Also found on teeth and tonsils.
• Trichomonas tenax: anaerobe found in gingival crevice.

They can be parasitic in nature, and ingest bacteria, leukocytes and erythrocytes.

Question 28

What are the 2 kinds of fungi prevalent in the oral cavity?

Answer 28

Molds and yeasts.

Question 29

Describe molds.

Answer 29

• Filamentous fungi
• Multicellular
• Structura units of molds are called hypha
• Hypha are divided at intervals by septa

Question 30

Describe yeasts.

Answer 30

• Unicellular, spherical bodies

- Can also be dimorphic e.g. Candida genus

Question 31

Describe candida.

Answer 31

A genus comprised of 150 species.
8 species recognised as opportunistic pathogens in humans.
E.g. C.albicans, C.tropicalis, C.krusei

Question 32

Describe the main features of microbial interactions.

Answer 32

• Presence of normal microflora affects the environment’s physical characteristics making it less favourable for colonisation by other microorganisms including pathogens
• E.g. lactobacilli lower the pH and produce hydrogen peroxide to inhibit growth of other microorganisms, lactobacilli produce biosurfactants to inhibit adhesion

Question 33

What species is the oral microflora dominated by?

Answer 33

α-haemolytic streptococci