the oral microflora - ecourse

M.R.Milward School of Dentistry

The Oral Microflora

1. Definitions

2. Microbial habitats

3. Factors affecting growth

4. Identification

5. Important oral bacteria

6. Clinical examples

7. Flora in dental plaque

8. Changes in the oral flora with age

9. Bacterial endocarditis

Contents

• Aetiology: The cause of phenomena (eg. disease)

• Pathology: Structural & functional changes caused by disease

• Pathogen(ic): Producing disease

• Pathogenesis: The mode of development of a disease

• Pathological: Relating to pathology or disease

• Commensal: An organism living in/on an organism of another species without injuring the host

• Parasite: An organism living in/on and at the expense of another organism (the host). Equivalent to a pathogen

• Opportunist Pathogen: A commensal organism that can cause disease in certain circumstances

• Symbiosis: The mutally beneficial association between two organisms

• Aerobic Organism: requiring oxygen for growth and replication

• Anaerobe: Organism that grows and replicates in the absence of oxygen; not necessarily killed by oxygen

• Strict anaerobe: Anaerobe killed by oxygen

• Facultative anaerobe: Organism capable of growth and replication in the presence or absence of oxygen

DEFINITIONS:

Oral Microbiology: PD Marsh & MV Martin

Microbial habitats Habitat Comment

Lips, cheek, palate •Biomass limited by desquamation •Some surfaces have specialised host cell types

Tongue •Highly papillated surface •Acts as a reservoir for obligate anaerobes

Teeth Non-shedding surface enabling large masses of microbes to accumulate (dental plaque biofilm) Teeth have distinct surfaces for microbial colonisation (e.g. Smooth surfaces, pits & fissures etc) will support distinct micro flora due to their biological properties

Gingival crevice / pocket

Health (aerobic), disease (anaerobic)

Oral Microbiology: PD Marsh & MV Martin

Oral Microbiology: PD Marsh & MV Martin

Factors Affecting Growth of Microorganisms in the oral cavity

1. Temperature

2. REDOX Potential / Anaerobiosis

3. pH

4. Nutrients (endogenous & exogenous (diet))

5. Host Defences (Innate & Acquired immunity)

6. Host genetics (changes in immune response etc)

7. Antimicrobial agents & inhibitors

Oral Microbiology: PD Marsh & MV Martin

Identification / classification

Characteristic Examples

Cellular morphology Shape, Gram staining, size, associations

Colonial appearance Pigmentation, haemolysis, shape, size

Carbohydrate fermentation Acid or gas production

Amino acid hydrolysis Ammonia production

Pattern of fermentation products

e.g. Lactate, acetate

Preformed enzymes e.g. glycosidases

Antigen Monoclonal/polyclonal antibodies to surface proteins

DNA Base composition

Pearson education

jlindquist.net

Bmb.leeds.ac.uk

GRAM POSITIVE = BLUE e.g. Streptococci, Staphylococci

GRAM NEGATIVE = RED/PURPLE e.g. E. coli, Fusobacterium, Porphyromonas

Complexity of Micro flora

Oral Microbiology: PD Marsh & MV Martin

Important Oral Bacteria

1. Gram Positive organisms: • Bulk of oral bacteria • Rods (bacilli), cocci or irregular shape (pleomorphic) • Oxygen tolerance varies from aerobes to strict anaerobes • Most are fermentative • Cell wall has thick peptidoglycan layer (penicillin has effect by interfering production of this layer) Three important genera: • Actinomyces, facultative anaerobe • Lactobacillus, produce lactic acid, facultative anaerobe, role in dentine caries rather than enamel caries • Streptococcus facultative anaerobic cocci, produce lactic acid some implicated in caries

Streptococci: • Isolated from all sights of the mouth • Large proportion of resident microflora • Majority α-haemolytic Strep mutans: • Associated with caries • Associated with bacterial endocarditis Strep salivarius: • Colonise mucosal surfaces especially the tongue

Strep angiosus: • Isolated dental plaque & mucosal surfaces • Seen in maxillofacial infections, brain, liver etc Strep mitis: • Opportunistic pathogens e.g. endocarditis

Important of Streptococci in the oral and their properties

Important

Oral Species

Growth on

hard

surfaces

Production of

Cariogenic Endocarditis

isolates

Insol.

Extracellular

polysaccharide

Acid

S mutans + + + +++ +

S sanguis + + + ++ ++

S mitior + + + + +++

S milleri + - + + +

S salivarius - - + - -

Distribution of Streptococci in the oral cavity

Species Cheek Tongue Saliva Tooth

S.mutans - - +/- ++

S. mitior +++ +++ +++ +++

S. salivarius - ++ ++ -

Actinomyces: • Short pleomorphic rods with branching • Major proportion of plaque • Increase in gingivitis • Associated with root caries

2. Gram Negative organisms Many Gram-negative bacteria found in the mouth, especially in established/subgingival plaque Cocci, rods, filamantous rods, spindle shaped or spiral shaped Range of oxygen tolerance but most important strict or facultative anaerobes Some fermentative, produce acids which other organisms use acids as an energy source, others produce enzymes which break down tissue Cell wall different to Gram positive with a thin peptidoglycan layer, has B-lactamase which breaks down penicillin, also has LPS/endotoxin

Important Oral Bacteria

Most important Gram negative bacteria:

• Porphyromonas: P. gingivalis major periodontal pathogen • Prevotella: P. intermedia a periodontal pathogen • Fusobacterium: F. nucleatum periodontal pathogen • Actinobacillus/Aggregatibacter: A.actinomycetemcomitans associated with aggressive periodontitis •Treponema: group important in acute periodontal conditions i.e ANUG • Neisseria • Veillonella

Clinical examples

Flora of normal, healthy dentate mouth

% (approx) Bacteria

85%

Streptococci

Veillonella

Gram positive Diptheroids

Gram negative anaerobic rods

5-7% Neissaeria

2% Lactobacilli

1% Staphylococci & Micrococci

2% Filamentous bacteria

Remainder Other bacteria, fungi, protozoa & viruses

Difference between mature supra & sub-gingival plaque

Characteristic Supra gingival Sub gingival

Grams stain Gram + or -ve Mainly Gram –ve

Morphotypes

Cocci, branching

rods, filaments &

spirochaetes

Mainly rods &

spirochaetes

Energy Metabolism Facultative, some

anaerobic Mainly anaerobic

Energy source Mainly ferment

carbohydrate

Many proteolytic

forms

Motility Few Many

Pathology Caries & gingivitis Gingivitis &

periodontitis

Distribution of bacteria in smooth surface dental plaque over 3 week

period

Bacteria Distribution (%)

6 hrs 1 day 2 days 7 days 3 wks

Gram +ve cocci 79 81 71 60 31

Gram +ve rods 8 7 10 20 56

Gram –ve cocci 5 5 11 12 9

Gram –ve rods 8 7 8 8 4

Oral flora changes with age

Time during a lifetime MAJOR COMPONENTS & CHANGES IN ORAL FLORA

Newborn Oral cavity sterile. Soon colonised by facultative and

aerobic organisms; esp S. salivarius

6 months Flora becomes more complex & includes anaerobic

orgs eg. Veillonella sp. & Fusobacteria

Tooth eruption

Increase in complexity. S sanguis, S mutans and A

viscosus appear. New habitats include hard surfaces

and gingival crevice.

Child to adult

Various anaerobes frequently found inc. Members

of the Bacteroidaceae. Spirochaetes isolated more

frequently

Loss of teeth Disappearance of S mutan, S sanguis, spirochaetes

and many anaerobes

Dentures etc Reappearance of bacteria able to grow on hard

surfaces

Bacterial endocarditis

Infective endocarditis (IE) is a rare condition with significant morbidity

and mortality. It may arise following bacteraemia in a patient with a

predisposing cardiac lesion. In an attempt to prevent this disease, over

the past 50 years, at-risk patients have been given antibiotic prophylaxis

before dental and certain non-dental interventional procedures.

Bacterial endocarditis is an infection in the lining of the heart or heart

valves, that could damage or destroy these valves. According to the

American Heart Association, bacterial endocarditis happens when

bacteria in the bloodstream, called bacteraemia, lodge on heart tissue

that has been damaged or on abnormal heart valves.

Bacterial endocarditis

escardio.org

Causative organisms in infective endocarditis:

Micro organism Cases (%)

TOTAL STREPTOCOCCI 60

Strep. viridans 35

Strep. faecalis 13

Microaerophilic Streptococci 3

Anaerobic Streptococci 2

Others 7

TOTAL STAPHYLOCOCCI 25

Staph. aureus 20

Staph. epidermidis 5

MISCELLANEOUS 5

CULTURE NEGATIVE 10

Adults and children with structural cardiac conditions: Regard people with the following cardiac conditions as being at risk of developing infective endocarditis: • acquired valvular heart disease with stenosis or regurgitation • valve replacement • structural congenital heart disease, including surgically corrected or palliated structural conditions, but excluding isolated atrial septal defect, fully repaired ventricular septal defect or fully repaired patent ductus arteriosus, and closure devices that are judged to be endothelialised • hypertrophic cardiomyopathy • previous infective endocarditis.

Advice Offer people at risk of infective endocarditis clear and consistent information about prevention, including: • the benefits and risks of antibiotic prophylaxis, and an explanation of why antibiotic prophylaxis is no longer routinely recommended • the importance of maintaining good oral health • symptoms that may indicate infective endocarditis and when to seek expert advice • the risks of undergoing invasive procedures, including non-medical procedures such as body piercing or tattooing.

When to offer prophylaxis Do not offer antibiotic prophylaxis against infective endocarditis: – to people undergoing dental procedures – to people undergoing non-dental procedures at the following sites1: upper and lower gastrointestinal tract genitourinary tract; this includes urological, gynaecological and obstetric procedures,and childbirth upper and lower respiratory tract; this includes ear, nose and throat proceduresand bronchoscopy. Do not offer chlorhexidine mouthwash as prophylaxis against infective endocarditis to people at risk undergoing dental procedures.

Managing infection Investigate and treat promptly any episodes of infection in people at risk of infective endocarditis to reduce the risk of endocarditis developing. Offer an antibiotic that covers organisms that cause infective endocarditis if a person at risk of infective endocarditis is receiving antimicrobial therapy because they are undergoing a gastrointestinal or genitourinary procedure at a site where there is a suspected infection.

Further Reading