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Oral Microbial Ecology. Ecology. Ecology (from Greek) is the scientific study of interactions among organisms and their environment, such as the interactions organisms have with each other and with their abiotic environment;
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Ecology Ecology (from Greek) is the scientific study of interactions among organisms and their environment, such as the interactions organisms have with each other and with their abiotic environment; The ecosystem is composed of microbial communities living on specific sites surrounded by a different physical and chemical elements.
Ecosystems Ecosystems are composed of dynamically interacting parts including organisms, the communities they make up, and the non-living components of their environment; Ecosystem processes, such as primary production, nutrient cycling, and various niche construction activities, regulate the flux of energy and matter through an environment.
Econiche Definitions of Hutchinson: “The set of biotic and abiotic conditions in which a species is able to persist and maintain stable population sizes."
Niche In ecology, a niche is a term describing the way of life of a species; Each species have a separate, unique niche; The ecological niche describes how an organism responds to the distribution of resources and competitors (e.g., by growing when resources are abundant, and when predators, parasites and pathogens are scarce) and how it in turn alters those same factors (e.g., limiting access to resources by other organisms, acting as a food source for predators and a consumer of prey).
Termite Termite mounds with varied heights of chimneys regulate gas exchange, temperature and other environmental parameters that are needed to sustain the internal physiology of the entire colony.
Microflora Living microorganisms that are so small that they can be seen only with a microscope and that maintain a more or less constant presence in a particular area; Includes bacteria, viruses, protozoa, fungi.
Oral microflora Oral microflora refers to the community of microorganisms coexisting in the oral cavity as its primary habitat; These strains of bacteria colonize the various different surfaces present in the oral cavity, and communicate between each other through complex cell signaling processes; The body’s own defenses also play a role in maintaining a balance and ensuring a healthy oral environment.
Normal - resident flora In a healthy body, the internal tissues - blood, brain, muscle, etc., are normally free of microorganisms; However, the surface tissues - skin and mucous membranes, are constantly in contact with environmental organisms and become readily colonized by various microbial species; The mixture of organisms regularly found at any anatomical site is referred to as the normal flora or resident flora, some researchers prefer the term "indigenous microbiota".
Resident microflora • Typical microflora of a econiche; • Microorganisms are separated and grouped according to the different conditions of life; • Resident microflora has an important function in host: • Digestive and nutritional; • Competition with pathogenic microflora.
Transient Microbiota • Transient microbes are just passing through; • Although they may attempt to colonize the same areas of the body as do resident microbiota, transients are unable to remain in the body for extended periods of time due to: • Competition from resident microbes; • Elimination by the body’s immune system; • Physical or chemical changes within the body that discourage the growth of transient microbes.
Opportunistic microbes Under normal conditions, resident and transient microbes cause the host no harm; However, if the opportunity arises, some of these microbes are able to cause disease and become opportunistic pathogens.
This can happen due to a number of different conditions: When the immune system isn’t working properly, normal flora can overpopulate or move into areas of the body where they do not normally occur; When the balance of normal microbes is disrupted, for example when a person takes broad spectrum antibiotics, microbes that are normally crowded out by resident microbes have an opportunity to take over; Disease can result when normal flora are traumatically introduced to an area of the body that they do not normally occur in.
Endogenous microflora That is microflora already present in the body, but has previously been inapparent or dormant. Bacterial flora is endogenous bacteria, which is defined as bacteria that naturally reside in a closed system.
Exogenous microflora Exogenous bacteria are microorganisms introduced to closed biological systems from the external world; They exist in aquatic and terrestrial environments, as well as the atmosphere; Microorganisms in the external environment have existed on Earth for 3.5 billion years; Exogenous bacteria can be either benign or pathogenic.
The origin of Oral Microflora The microflora present in our mouths is acquired from birth, as newborn babies have no bacteria in their mouths; Over time, the oral cavity becomes colonized by the strains of bacteria that eventually form the resident microflora, which establish a permanent population in the mouth; Over time as the individual is further exposed to external sources of bacteria, the biodiversity of the oral cavity increases, to a point where stability is reached. This is termed the climax community.
The source of microorganisms The source of these microorganisms mainly comes from saliva, although it also includes the food and water consumed by the individual; This process takes place within the first few hours of life; Majority of children obtain their resident microflora from their mothers, as they often possess identical strains of bacteria; This is known as vertical transmission; Horizontal transmission also takes place as children interact with their peers, and later in life between spouses and partners.
Formation of the ecosystem The development of microbial community comprises an alternation of populations; The process starts with the colonization of the environment of the first microbial population; It fills the new space, modify it and makes it convenient for resettlement of new microbial population.
This process continues Growing microbial community was enriched with different species living in complex; The process of alternation of populations and enrichment of the community stops only when no available niches for colonization of new microbial species.
Climax community The settlement of all econiches occurs relative stability of the system by the microorganisms – called climax community; The stability of the community is based on the homeostasis, including compensatory mechanisms against the effects of various factors.
Bacteria during the life cycle • Oral colonization begins in the birth canal: • Populations on the tongue and mucosa; • Established during infancy - include anaerobes; • Tooth eruption provides non-shedding surfaces: • The “window of infectivity” concept; • Colonization from source sites and caregiver saliva; • Hormonal shifts - puberty and pregnancy: • Can alter proportions of Gm- anerobes; • Complete loss of teeth shifts flora towards infant state: • Dentures restore supragingival non-shedding sites; • Implants restore supra- and subgingival sites.
Microflora at birth At birth, the oral cavity is composed only of the soft tissues of the lips, cheeks, tongue and palate, which are kept moist by the secretions of the salivary glands. At birth the oral cavity is sterile but rapidly becomes colonized from the environment, particularly from the mother in the first feeding. Streptococcus salivariusis dominant and may make up 98% of the total oral flora until the appearance of the teeth (6 - 9 months in humans).
Periods of formation of the oral ecosystem • The neonatal period: • Mostly aerobes; • Candida albicans - 54%; • Obtained from the mother and the surrounding area; • Period before eruption: • Facultative anaerobes and anaerobes; • Streptococcus - 90%; • Actinomyces; • Candida albicans.
After eruption The eruption of the teeth during the first year leads to colonization by S. mutansand S. sanguis; These bacteria require a nondesquamating (nonepithelial) surface in order to colonize; They will persist as long as teeth remain; Other strains of streptococci adhere strongly to the gums and cheeks but not to the teeth.
Period after eruption • Anaerobes: • Actinomyces; • Lactobacillus; • Veillonella; • Fusiformis; • Spirochetes; • Candida albicans.
Oral surfaces The oral cavity contains various different forms of tissue which have different properties; The microflora in the mouth is distributed according to the different types of surfaces present, which provide each particular species with its optimal growing environment; Certain breeds of bacteria are dependent on specific surfaces to adhere to.
Diverse ecological niches in the oral cavity The heterogeneity of tissue types in the oral cavity, such as teeth, tongue and mucosa, means that a variety of sites are available for colonization by oral microorganisms; Each site has unique characteristics and allows those microorganisms best suited to the environment to inhabit the site; The role of microorganisms in a habitat is referred as an ecological niche and a number of ecological niches exist in the oral cavity, including supragingival plaque, subgingival plaque and tongue coating. These ecological niches can be characterized by the environmental factors and the metabolic characteristics of the microbial flora occupying these sites.
Mucosal Surfaces: • These include the palate, cheek and tongue, which have cells which are constantly replaced due to the normal wear-and-tear of the mouth; • The different mucosal surfaces also have different properties which contribute to the presence of different types of bacteria: • Areas such as the palate contain keratinized squamous epithelium and the softer non-keratinized areas such as the cheeks; • The tongue is a unique surface with papillary structures, which provides ample crevices for a wide variety of different strains of bacteria to reside; • The presence of these crypts allows for bacteria to be protected from the normal shedding and removal by saliva flow, and hence species not found elsewhere, such as obligate anaerobes, can be found on the dorsum of the tongue.
Mucosal reservoir sites • Smooth exfoliating surfaces: • How do bacteria keep from being swept away? • Some oral species can invade epithelial cells: • Requires communication between bacteria and cells; • Bacteria “subvert” the cell to take them in: • Take control of the cytoskeleton; • Can live and grow inside; • Can direct the cell to export them to other cells; • Multi-species intracellular flora resembles mixed biofilm.
Oral econiches • Hard structures – teeth, providing various locations for colonization: • Subgingival; • Supragingival; • Soft structures – mucosa: • Cheeks, lips, tongue, gingiva, palate; • Keratinized and nonkeratinized mucosa; • Epithelium of the gingival sulcus.
Mucosa of the gingiva, palate, cheek, floor of the mouth • Streptococcus: • S. oralis, S. sanguis; • Neisseria; • Haemophilus; • Veillonella.
Surface of the tongue Streptococcus salivarius, S. mitis; Veillonella spp.; Peptostreptococcus spp. Gram + rods - Actinomyces spp.; Gram - rods - Bacteroides spp.; Obligate anaerobes black - rods and spirochetes associated with periodontal diseases.
Dental econiches • Supragingival plaque: • On approximal surfaces; • On occlusal surfaces - fissures, pits and grooves; • Cervical; • Gram positive MO; • Facultative anaerobes: • Streptococcus; • Actinomyces; • Gram negative: • Veillonella, Haemophilus, Bacteroides
Subgingival plaque • From healthy gingival sulcus isolate: • Gram negative rods: • Porphyromonasgingivalis; • Porphyromonasendodontalis; • Prevotellamalaninogenica; • Prevotellaintermedia; • Prevotellaloesheii; • Prevotelladenticola.
Subgingival tooth surfaces Narrow crevice between gingival epithelium and cementum Low oxygen tension favorable for Gm- anaerobes; Major site for interaction between bacteria and host tissues; Species mix varies between each side and the center- distinct microenvironments.
Microorganisms in saliva Depend on the microorganisms of all ecological niches; Microbial composition of saliva is the most similar to the tongue.
Oral fluids • Oral surfaces washes of two liquids: • Saliva; • Gingival fluid; • They are the basis for maintaining oral ecosystem: • Provide water; • Nutrients; • Adhesion; • Antimicrobial factors.
Pathogenicity of microflora Microflora usually is non-pathogenic and form an integral part of the host; The presence of friendly resident microorganisms on oral surfaces contributes to the body’s defense against foreign pathogens, which are generally transient and can give rise to harmful infections. This is known as colonization resistance;
Function of Microflora Colonization resistance is firstly achieved through the saturation of oral surfaces with preexisting resident bacteria, which reduces the available sites left for the attachment of exogenous organisms; Essential nutrients derived from the saliva and various proteins in the oral cavity are also more effectively utilized by the resident microflora, which inhibits infections via competition for resources;
Resident microflora modified the conditions of the mouth It maintains unfavorable conditions for invading microbes; Producing substances such as hydrogen peroxide that actively inhibits pathogen growth; As a result, the harmony between the oral microflora and the body’s natural defenses acts as an effective deterrent to infections, and thus maintains the health of the host.
Variations in Microflora Everyone has microflora, but it varies between people depending on the condition of their oral cavity; Not all individuals would have the same microflora profile; Not all bacteria are ubiquitous in all individuals.
Gingival crevicular fluid: At the gingival margin, serum flows from the inside the gingiva into the mouth; The flow of this fluid removes foreign microbes which do not adhere to these surfaces; For the resident population, the flow of crevicular fluid provides these organisms with a source of nutrition; They have specialised enzymes which can break down these proteins to provide them with the nutrients necessary for growth.
Teeth and artificial hard surfaces: Microbes can accumulate on teeth; This generally forms a dense layer of bioflim known as dental plaque; Fissures and deep grooves in the teeth provide ideal conditions for the formation and build-up of dental plaque; Most of the bacteria found in dental plaque is absent in individuals without teeth, such as babies.
The role of salivain the maintenance of a healthy oral environment By acting as a buffer, saliva maintains the pH of the mouth, ensuring the optimal growth of the resident colonies; Most of the microbes present in the mouth utilize the glycoproteins and proteins in the saliva as their main source of nutrition; Proteins and glycoproteins of saliva are responsible for the formation of the pellicle, a film on the surface of the tooth enamel where the microorganisms of the microflora can adhere to.
Salivary flow It is responsible for the removal of non-endogenous bacteria which is unable to adhere to specific sites in the mouth; Saliva acts a collector of these cells and facilitates their removal; Areas which receive markedly less saliva flow, such as deep gingival crevices, proximal spaces and occlusal fissures, tend to have significantly higher levels of bacterial buildup; Saliva is carrying bacteria - the main source of microbial transmission between individuals; Saliva also circulates bacteria within the oral cavity, resulting in re-colonization of oral surfaces where the microflora might be removed via mechanical forces such as cleaning.
The normal bacterial flora of the oral cavity Benefit from the host who provides nutrients and habitat; Occupy available colonization sites which makes it more difficult for other microorganisms to become established; Contribute to host nutrition through the synthesis of vitamins, and they contribute to immunity by inducing low levels of circulating and secretory antibodies that may cross react with pathogens; Exert microbial antagonism against exogenous species by production of inhibitory substances such as fatty acids, peroxides and bacteriocins.
The oral flora are the usual cause of various oral diseases Abscesses, dental caries, gingivitis, and periodontal disease; If oral bacteria can gain entrance into deeper tissues, they may cause abscesses of alveolar bone, lung, brain, or the extremities; Such infections usually contain mixtures of bacteria with Bacteroidesmelaninogenicus often playing a dominant role; If oral streptococci are introduced into wounds created by dental manipulation or treatment, they may adhere to heart valves and initiate subacute bacterial endocarditis.
DEFINITIONS: • 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; Opportunistic Pathogen: A commensal organism that can cause disease in certain circumstances ; Symbiosis: The mutually 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;
Members of Human Resident oral microflora Gram-positive bacteria
