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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
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