Periodontal Microbiology PDF

Biofilm and Periodontal Microbiology NEWMAN AND CARRANZA’S CLINICAL PERIODONTOLOGY 1 3 TH E D. C H A PTE R 8 , B I O F I L M A N D P E R I O D O N T A L MICROBIOLOGY - PAGE 1 12 -150. ASSOC. PROF. REHAM AGGOUR Objectives Understanding microbial etiology and pathogenesis...

Biofilm and Periodontal Microbiology NEWMAN AND CARRANZA’S CLINICAL PERIODONTOLOGY 1 3 TH E D. C H A PTE R 8 , B I O F I L M A N D P E R I O D O N T A L MICROBIOLOGY - PAGE 1 12 -150. ASSOC. PROF. REHAM AGGOUR Objectives Understanding microbial etiology and pathogenesis  Biofilm  Plaque formation  Pathogenicity (virulence) of pathogens ◼ Virulence factors Our body contains 1.3 to 10 times more bacteria than human cells Most oral bacteria are harmless commensals under normal circumstances. This means that this microbiota lives in harmony with its host but under specific conditions (i.e., increased mass and/or pathogenicity, suppression of commensal or beneficial bacteria, and/ or reduced host response), disease can occur. The Oral Cavity From a Microbe’s Perspective NEWMAN AND CARRANZA’S CLINICAL PERIODONTOLOGY – CHAPTER 8 – PAGE 112 - Streptococcus salivarius and Streptococcus mitis Veillonella spp., Neisseria spp., Actinomyces spp. → First colonizers of the oral cavity - Oral bacterial microbiome of adults → approximately 700 species - The periodontal microbiota is extremely complex. Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 114 Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 115 Most organisms can survive in the oropharynx only when they adhere to either the soft tissues or the hard surfaces. Otherwise removed by: Swallowing, mastication, or blowing the nose Tongue and oral hygiene implements The wash-out effect of the salivary, nasal, and crevicular fluid outflows The active motion of the cilia of the nasal and sinus walls Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 113  - The ability of a bacterium to adhere to its host is crucial for the induction of gingivitis and periodontitis. - A positive correlation exists between the adhesion rate of pathogenic bacteria to different epithelia and the susceptibility of the affected patient to certain infections Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 113 Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 118 The oral cavity can be divided into six major ecosystems (niches) 1. The intraoral and supragingival hard surfaces (teeth, implants, restorations, and prostheses) 2. Subgingival regions adjacent to a hard surface, including the periodontal/peri-implant pocket (crevicular fluid, the root cementum or implant surface, and the pocket epithelium) 3. The buccal palatal epithelium and the epithelium of the floor of the mouth 4. The dorsum of the tongue 5. The tonsils 6. The saliva Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 113 The soft tissue surfaces use a variety of mechanisms to prevent the adhesion of pathogenic organisms: ❑ Shedding. The epithelial cells are shed twice a day in a process known as desquamation Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 115-116  Microbiologically, teeth and implants are unique for two reasons: (1) they provide a hard, no shedding surface that allows for the development of extensive structured bacterial deposits; (2) they form a unique ectodermal interruption. A special seal of epithelium and connective tissue is present between the external environment and the internal parts of the body. The accumulation and metabolism of bacteria on these hard surfaces are the primary causes of caries, gingivitis, periodontitis, peri-implantitis, and, sometimes, bad breath. Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 116  Bacteria and Their Biofilm Mode of Living- Interface - Biofilms are composed Microbial cells encased within a matrix of extracellular polymeric substances, such as polysaccharides, proteins, and nucleic acids. - 1000 times more resistant to antimicrobial agents than their planktonic counterparts because The matrix functions as a barrier. Substances produced by bacteria within the biofilm are retained and concentrated, which fosters metabolic interactions among the different bacteria. - Multispecies beneficial interactions - Compete with their neighbors (antibacterial molecules such as inhibitory peptides (bacteriocins) or hydrogen peroxide (H2O2) - Cell–cell signaling and (DNA) exchange between bacteria Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 117 The nature of biofilms ◼ Provides advantages for colonizing species  Protection from ◼ Competing microorganisms ◼ Environmental factors, host defense ◼ Toxic substances, such as lethal chemicals, antibiotics  Facilitate processing and uptake of nutrients, cross-feeding, removal of harmful metabolic products  Development of an appropriate physico-chemical environment Common structural features of biofilms - Microcolonies of bacterial cells - Water channels; primitive circulatory system - Distribution heterogeneity ; microenvironments [oxygen , pH,….] Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 119  Bacteria are also found within the host tissues, such as in the soft tissues, and within epithelial cells, as well as in the dentinal tubules Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 118 Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 123 Structure of the intercellular matrix - Constituents are derived from saliva, gingival crevicular fluid, and bacterial products Organic constituents (Glycoproteins from the saliva, Polysaccharides produced from bacteria, lipid from the membranes of disrupted bacterial and host cells and food debris…….) - The inorganic components (predominantly calcium and phosphorus) ❑The source of inorganic constituents of supragingival plaque is primarily saliva. As the mineral content increases, the plaque mass becomes calcified to form calculus ❑The inorganic components of subgingival plaque are derived from crevicular fluid (a serum transudate) Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 119 Structure of a Mature Dental Plaque Biofilm A structured, resilient, yellow-grayish substance that adheres tenaciously to the intraoral hard surfaces, including removable and fixed restorations composed primarily of microorganisms(more than 750 distinct microbial phylotypes) NOT: Materia Alba OR Calculus Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 119 Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 122 Dental plaque Based on its position on the tooth surface toward the gingival margin: - Supragingival : stratified organization of a multilayered accumulation of bacterial morphotypes: Gram-positive cocci and short rods predominate at the tooth surface, gram-negative rods, filaments, and spirochetes predominate in the outer surface of the mature plaque mass. - When in direct contact with the gingival margin, it is referred to as marginal plaque - Subgingival - Between the tooth and the gingival pocket epithelium. - Differs in composition from the supragingival plaque, primarily because of the local availability of blood products and a low reduction–oxidation (redox) potential, which characterizes the anaerobic environment. Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 122 Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 121.e1 Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 121  Subgingival plaque: - tooth-associated - soft tissue–associated Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 120 - The composition of the subgingival plaque depends on the pocket depth. The apical part is more dominated by spirochetes, cocci, and rods, whereas in the coronal part more filaments are observed. - The apical border of the plaque mass is separated from the junctional epithelium by a layer of host leukocytes, and the bacterial population of this apical-tooth–associated region shows an increased concentration of gram-negative rods(periodontopathogens) Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 121.e2 Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 121.e3  Many strains of Actinomyces coaggregate with oral streptococci, and therefore the spatial organization of these organisms within dental plaque may be influenced by adhesin–receptor interactions Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 121.e4 Site specificity of plaque ❑Marginal plaque, is of prime importance during the initiation and development of gingivitis. ❑ Supragingival plaque and tooth-associated critical in calculus formation and root caries ❑tissue-associated subgingival plaque is important in the tissue destruction that characterizes different forms of periodontitis. Accumulation of a Dental Plaque Biofilm Divided into several phases: (1) the formation of the pellicle on the tooth surface (2) the initial adhesion/attachment of bacteria (3) colonization/plaque maturation. Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 122 1. Formation of the Pellicle ❑The salivary pellicle can be detected on clean enamel surfaces within 1 minute after their introduction into the mouths of volunteers. ❑ By 2 hours, the pellicle is essentially in equilibrium between adsorption and detachment, although further pellicle maturation can be observed for several hours. ❑The pellicle is composed of two layers: a thin basal layer that is very difficult to remove, even with harsh chemical and mechanical treatments, and a thicker globular layer, up to 1 µm or more, that is easier to detach. Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 123-124 1. Formation of the Pellicle ❑Bacteria that adhere to tooth surfaces do not contact the enamel directly but interact with the acquired enamel pellicle. ❑ The pellicle is not merely a passive adhesion matrix. Many proteins retain enzymatic activity when they are incorporated into the pellicle, and some of these, such as peroxidases, lysozyme, and α-amylase, may affect the physiology and metabolism of adhering bacterial cells. Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 123-124 2. Initial Adhesion/Attachment of Bacteria ❑Colonizing bacteria detected within 3m after the introduction of sterile enamel into the mouth. ❑The interactions between microbial cell surface “adhesin” and receptors in the pellicle determine whether a bacterial cell will remain associated with the surface. Only a small proportion of oral bacteria possess adhesins that interact with receptors in the host pellicle. ❑Over the first 4 to 8 hours, Streptococcus dominate, usually. Other bacteria present at this time include species that cannot survive without oxygen (obligate aerobes), such as Haemophilus spp. and Neisseria spp., as well as organisms that can grow in the presence or absence of oxygen (facultative anaerobes), including Actinomyces spp. and Veillonella spp. ❑ These species are considered the “primary colonizers” of tooth surfaces. ❑The primary colonizers provide new binding sites for adhesion by other oral bacteria. The metabolic activity of the primary colonizers modifies the local microenvironment. For example, by removing oxygen, the primary colonizers provide conditions of low oxygen tension that permit the survival and growth of obligate anaerobes. Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 124 3. Colonization and Plaque Maturation ❑The primary colonizing bacteria provide new receptors for attachment by other bacteria as part of a process known as coadhesion (coaggregation). Together with the growth of adherent microorganisms, coadhesion leads to the development of microcolonies and eventually to a mature biofilm. ❑Different species—or even different strains of a single species— have distinct sets of coaggregation partners. Adhesion is mediated by lectin-like adhesins. ❑The transition from early dental plaque to mature plaque growing below the gingival margin involves a shift in the microbial population from primarily gram- positive organisms to high numbers of gram-negative bacteria. ❑During the later stages of plaque formation, coaggregation among different gram-negative species is likely to predominate. Examples: coaggregation of F. nucleatum with P. gingivalis or Treponema denticola Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 124 Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 124 Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 124.e2 Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 125 Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 125 Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 126.e1 Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 126.e2 Metabolism of Dental Plaque Bacteria 1. The transition from gram-positive to gram-negative microorganisms observed in the structural development of dental plaque is paralleled by a physiologic transition in the developing plaque 2. The early colonizers (e.g., Streptococcus and Actinomyces spp.) use oxygen and lower the redox potential of the environment, which then favors the growth of anaerobic species. 3. Gram-positive early colonizers use sugars as an energy source. The bacteria that predominate in mature plaque are anaerobic and asaccharolytic (i.e., they do not break down sugars), and they use amino acids and small peptides as energy sources. 4. Many metabolic interactions occur among the different bacteria found in dental plaque Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 129 Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 130 Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 131 Factors That Affect Supragingival Dental Plaque Formation Topography of Supragingival Plaque Early plaque formation on teeth follows a typical topographic pattern (Fig. 8.18), with initial growth along the gingival margin and from the interdental spaces (i.e., the areas protected from shear forces). Later, a further extension in the coronal direction can be observed. This pattern may change when the tooth surface contains irregularities that offer a favorable growth path Newman and Carranza’s Clinical Periodontology – Chapter 8 – Page 126