The Oral Microflora. M.R.Milward School of Dentistry

Transcription

1 The Oral Microflora M.R.Milward School of Dentistry

2 Contents 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

3 Aetiology: The cause of phenomena (eg. disease) Pathology: Structural & functional changes caused by disease Pathogen(ic): Producing disease DEFINITIONS: 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

4 Oral Microbiology: PD Marsh & MV Martin

5 Microbial habitats Habitat Lips, cheek, palate Tongue Teeth Gingival crevice / pocket Comment Biomass limited by desquamation Some surfaces have specialised host cell types Highly papillated surface Acts as a reservoir for obligate anaerobes 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 Health (aerobic), disease (anaerobic)

6 Oral Microbiology: PD Marsh & MV Martin

7 Oral Microbiology: PD Marsh & MV Martin

8 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

9 Oral Microbiology: PD Marsh & MV Martin

10 Identification / classification Characteristic Cellular morphology Colonial appearance Carbohydrate fermentation Amino acid hydrolysis Pattern of fermentation products Preformed enzymes Antigen DNA Examples Shape, Gram staining, size, associations Pigmentation, haemolysis, shape, size Acid or gas production Ammonia production e.g. Lactate, acetate e.g. glycosidases Monoclonal/polyclonal antibodies to surface proteins Base composition

11

12

13

14 Pearson education

15 jlindquist.net

16 Bmb.leeds.ac.uk

17 GRAM POSITIVE = BLUE e.g. Streptococci, Staphylococci GRAM NEGATIVE = RED/PURPLE e.g. E. coli, Fusobacterium, Porphyromonas

18 Complexity of Micro flora Oral Microbiology: PD Marsh & MV Martin

19 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

20 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

21 Important of Streptococci in the oral and their properties Production of Important Oral Species Growth on hard surfaces Insol. Extracellular polysaccharide Acid Cariogenic Endocarditis isolates S mutans S sanguis S mitior S milleri S salivarius

22 Distribution of Streptococci in the oral cavity Species Cheek Tongue Saliva Tooth S.mutans - - +/- ++ S. mitior S. salivarius

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

24 Important Oral Bacteria 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

25 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

26 Clinical examples

27

28

29

30

31

32

33

34

35

36 Flora of normal, healthy dentate mouth % (approx) Bacteria 85% Streptococci Veillonella 5-7% Neissaeria 2% Lactobacilli Gram positive Diptheroids Gram negative anaerobic rods 1% Staphylococci & Micrococci 2% Filamentous bacteria Remainder Other bacteria, fungi, protozoa & viruses

37 Difference between mature supra & sub-gingival plaque Characteristic Supra gingival Sub gingival Grams stain Gram + or -ve Mainly Gram ve Morphotypes Cocci, branching Mainly rods & rods, filaments & spirochaetes spirochaetes Energy Metabolism Facultative, some anaerobic Mainly anaerobic Energy source Mainly ferment Many proteolytic carbohydrate forms Motility Few Many Pathology Caries & gingivitis Gingivitis & periodontitis

38 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 Gram +ve rods Gram ve cocci Gram ve rods

39 Oral flora changes with age Time during a lifetime Newborn 6 months Tooth eruption Child to adult Loss of teeth Dentures etc MAJOR COMPONENTS & CHANGES IN ORAL FLORA Oral cavity sterile. Soon colonised by facultative and aerobic organisms; esp S. salivarius Flora becomes more complex & includes anaerobic orgs eg. Veillonella sp. & Fusobacteria Increase in complexity. S sanguis, S mutans and A viscosus appear. New habitats include hard surfaces and gingival crevice. Various anaerobes frequently found inc. Members of the Bacteroidaceae. Spirochaetes isolated more frequently Disappearance of S mutan, S sanguis, spirochaetes and many anaerobes Reappearance of bacteria able to grow on hard surfaces

40 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.

41 Bacterial endocarditis escardio.org

42 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

43

44 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.

45 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.

46 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.

47 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.

48 Further Reading