Oral Microbiology 1 PDF

 Dr. Mona Abd El-Hamid Abd El-Raouf lecturer of Medical Microbiology & Immunology Department of Medical Microbiology & Immunology, Faculty of Medicine, Mansoura University  Introduction  The normal flora of the mouth: ◦ Types of oral microbial flora (bacteria,...

 Dr. Mona Abd El-Hamid Abd El-Raouf lecturer of Medical Microbiology & Immunology Department of Medical Microbiology & Immunology, Faculty of Medicine, Mansoura University  Introduction  The normal flora of the mouth: ◦ Types of oral microbial flora (bacteria, fungi and viruses) ◦ Microbial flora at different parts of the mouth. ◦ Change of oral flora by age  Oral infection: ◦ Sources ◦ Predisposing factors. ◦ Examples  ILOs  By the end of this lecture, students will be able to: ◦ Describe the content and distribution of oral flora. ◦ Explain the relation between oral flora and infection. ◦ Discuss some of important bacterial oral infections.  Introduction Oral microbiology is the study of the microorganism of the oral cavity and their interactions between or with the host. Resident microbes of the mouth adhere to the teeth and gums to resist mechanical flushing from the mouth to stomach where acid- sensitive microbes are destroyed by HCL  Introduction  Saliva contains approximately 108 bacteria per milliliter.  The organisms present in saliva do not represent a resident population but are organisms that have been dislodged from the oral surfaces, especially the tongue.  The presence of oral commensal flora provides protection from overgrowth by pathogens including Streptococcus pyogenes, Streptococcus pneumoniae, and Candida albicans.  Saliva also contains digestive enzymes and a number of anti-microbial compounds including; ◦ Secretory IgA ◦ Lysozyme ◦ lactoferrin.  The normal flora of the mouth  The mouth is colonized by a characteristic commensal microflora, including bacteria, fungi, viruses and occasionally protazoa.  Bacteria are the predominant components of this resident microflora.  The composition of the microbial flora varies considerably from site to site of the mouth and at different times.  The composition of the oral microflora is highly complex and variable.  At least 700 different species are known to be associated with the oral cavity. Gram positive bacilli Gram negative bacilli  Composition of Oral Microbial Flora A) Bacteria I)Gram +ve cocci:  Staphylococci; especially S.epidermidis,  Streptococci:  - haemolytic or viridans streptococci and B- haemolytic streptococci are present in mouth.  Streptococci constitute the major bacterial group in the oral cavity. They are associated with plaque formation and acid production from carbohydrates. Streptococcus viridans are of particular importance in cases of tooth extraction in patients with heart valve disease. II) Gram +ve bacilli: Diphtheroid: aerobe, found normally in mouth. Nocardia: strict aerobes. Actinomyces: anaerobe , found between teeth and in gum grooves, major member in dental plaque. Lactobacilli: produce large amounts of acids from carbohydrates. III) Gram –ve cocci: Moraxella catarhalis: aerobic Neisseria: aerobic or microaerophilic. Veillonella: anaerobe.  IV) Gram- negative bacilli:  Bacteroids: strict anaerobes.  Fusibacterium: strict anaerobes Capnocytophagia certain species which are found in the gum region of molars are believed to be involved in peridontal disease. V) Spirocheates:  Borrelia: strict anaerobes.  Treponema: strict anaerobes.  B) Fungi  Candida: ◦ the most common fungi present in oral cavity. ◦ Present in small percentage of the total oral flora in normal healthy mouth. ◦ Increase in number and may cause infections in diabetic patients, cancer, immune deficiency disorders as AIDS and after heavy doses of antibiotics & in pregnancy.  C) Viruses  Little is known about the role of virus in normal oral flora, but some viruses as herpes simplex, measles, mumps can be found in oral lesions during the course of the disease.  HIV virus and hepatitis viruses may be present in saliva during the disease. Change of oral flora by age: Microbial flora at different parts of the mouth  Many factors affect microbial flora at different sites due to conditions at these sites vary with respect to: Oxygen levels and anaerobiosis. Availability of nutrients Exposure to salivary secretions Mastication forces other variables such as oral hygiene.  Strept salivarius: is the predominant on dorsal surface of the tongue.  Strept Sangius:: is the predominant on the buccal mucosa.  Strept Mitior: colonize the smooth surface of teeth.  Strept.mutans: colonize the occlusal pits and fissures of crowns.  BBacteroides melaninogenicus and oral spirochetes: prefer the gingival crevice.  Content  Oral infections: ◦ Sources ◦ Predisposing factors. ◦ Examples  Oral infections Origin of infection: Oral infection may arise from: a- Endogenous source involving microorganisms normally found in the mouth such as those associated with the plaque, related conditions of caries and periodontal disease. b- Exogenous source  less common than endogenous infections  subdivided into: 1. Primary infections such as herpes simplex or primary syphilis 2. Secondary manifestations of systemic infections, such as oral tuberculosis and secondary syphilis.  Predisposing factors that lead to oral infections:  Normally there is balance between oral microflora and the host.  This balance can be disrupted resulting in disease of the oral structure.  The oral flora together with other oral defense mechanisms plays an important role in protecting the oral cavity from infections by exogenous organisms.  Disturbances to the oral cavity may allow Displacement of Selective certain Introduction of overgrowth of endogenous exogenous certain species, for microorganisms, endogenous example such as Escherichia species as Candida actinomyces israelili coli that can cause albicans, in patients with resulting osteomyelitis after with HIV infection or actinomycosis after radiotherapy AIDS. trauma to the mucosa or jaws.  These predisposing factors are: old age→ cause diminished antibody levels, decrease in salivary flow→ lead to candidosis, Physiological root caries. factor leading to gingivitis Pregnancy Local trauma leading to loss of tissue integrity → opportunistic infection General trauma debilitation, dehydration→ Trauma: leading to candidiasis.  deficiencies of iron, vitamin B12→ leading to Malnutrition: candidiasis. diminished cell mediated immunity→ opportunistic AIDS: infections, candidiasis. disrupts the balance of the oral flora causing selection of resistant microflora→ leading to Chemotherapy: opportunistic infectious, candidiasis and caries. Oral leading to candidiasis & caries. malignancies:  I) Bacterial infections The most common oral infections are: 1. Infected dry socket:  With dry socket, the blood clot that forms following tooth extraction is dislodged and lost from the extraction site thus exposing the bone and nerves allowing infection to occur.  The bony walls of the socket often show signs of tissue death and become infiltrated with bacteria of many types.  A foul odor also occurs. 2. Periodontal disease:  Diseases of the gingival and alveolar bone which supports the teeth (periodontal disease).  Endodontic infections: that involve the pulp of the tooth after trauma or carious exposure.  Periapical infections: resulting from extension of bacteria from infected pulp through the apex of the tooth.  Abscesses: may form from periapical infections or from deep periodontal pockets.  Periodontitis  Periodontitis is an inflammation of the periodontium (gingiva, cementum. alveolar bone and periodontal ligament) that surround and support the teeth→ these disease are the major cause of loss of teeth in adults.  Pathogenesis  Pathogenesis is multi-factorial and results from the interaction of the body and its defense mechanisms with products from bacterial plaque. ▪ When gingivitis is not treated, it turns into periodontitis, which means inflammation around the teeth. ▪ Inflammation causes pockets around the tooth that become infected. ▪ Plaque spreads and grows below the gum line. ▪ Bacterial toxins and the body's natural response to infection start to break down the bone and connective tissue that hold teeth in place. ▪ If not treated, the bones, gums, and tissue that support the teeth are destroyed. ▪ The teeth may eventually become loose and have to be removed. The mechanisms of periodontal destruction include: ◦ Collagenase, ◦ Hyaluronidase, ◦ Protease, ◦ DNAse, and other enzymes ◦ Cytotoxic agents as endotoxins, ◦ Cell wall peptidoglycan. ◦ Cell mediated immunity with lysozyme activation ◦ Complement activation by endotoxin or immune complex→ cell destruction and damage.  Histologic and clinical changes:  After plaque accumulation & within 2 weeks→ gingivitis (gingiva show histologic changes called established lesion with plasma cell infiltrate of sub-epithelial connective tissue) in some persons, the disease remains at this level.  Majority of cases progress with time→ there is resorption of supporting alveolar bone, formation of soft tissue pockets between the teeth and gingiva.  Bacteria represents the main component of normal oral flora.  The disturbance in oral cavity usually leads to oral infection. 11/16/2023 45