Spirillum. 7. Spirochete. 3.Depending upon influence of oxygen on growth and viability. 1.Aerobes: Required O2 for growth. 2.Anaerobes: Obligate: Grows in ...
FLORA OF ORAL CAVITY
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Table of Contents Prologue Chapter 1: Classification Chapter 2: Acquisition of normal oral flora Chapter 3: Gram positive cocci Chapter 4: Gram positive rods & filaments Chapter 5: Gram negative cocci Chapter 6: Gram negative rods-facultative anaerobs Chapter 7: Gram negative rods-obligate anaerobs Chapter 8: Fungi Chapter 9: Mycoplasma Chapter 10: Viruses Chapter 11: Protozoa Chapter 12: The oral ecosystem Chapter 13: Host-bacteria interrelationship Chapter 14: Microbiology of dental caries Chapter 15: Microbiology of periodontal diseases Conclusion About author
Prologue The oral flora comprises a diverse group of organisms and includes bacteria, fungi, mycoplasmas, protozoa and possibly a virus flora.Bacteria are by far the predominant group of organisms.The diversity of oral flora is due to the fact that the mouth is composed of varied habitats supplied with a range of different nutrients. A plethora of research had been done in oral microbiology,which showed variety of facts and results.The microorganisms found in different areas of the oral cavity differs in their characteristics regarding the nutritional requirement, oxygen dependence,metabolic activity and so on. Hence the same species of microorganism isolated from different part of the oral cavity may show different characteristics with respect to their growth, nutritional requirement and metabolic activity.
Chapter 1: Classification of microbial flora 1.Depending upon staining Gram positive – Resist decolourisation and retain the primary stain appearing violet.They have thicker cell wall that prevents the decolorisation by organic acid. Gram Negative – Decolorized by organic solvents and take up the counter stain appearing red.
2.Depending upon morphology: 1. Coccus 2. Bacillus 3. Coccobacilli 4. Fusiformbacilli 5. Vibrio
6. Spirillum 7. Spirochete 3.Depending upon influence of oxygen on growth and viability. 1.Aerobes: Required O2 for growth. 2.Anaerobes: Obligate: Grows in the absence of O2. Facultative: Grow in the presence or absence of O2. 3.Microaerophilic
Chapter 2: Acquisition of the normal oral flora Infants mouth is sterile at birth.A few hours later the organisms from the mother’s mouth and possibly a few from the environment are established in the mouth.These pioneer species are usually Streptococci,which binds to mucosal epithelium(Strept.salivarius). The metabolic activity of the pioneering community then alters the oral environment to facilitate colonization by other bacterial genera and species. When the composition of this complex ecosystem reaches equilibrium, a climax community is said to exist.Oral flora on the child’s first birthday usually consists of Streptococci , Staphylococci , Neisseria , Lactobacilli, Veillonella, Fusobacteria. Less frequently isolated are Actinomyces, Prevotella, Porphyromonas species.
The next evolutionary change in this community occurs during and after tooth eruption when two further niches are provided for bacterial colonization: the hard tissue surface of enamel and the gingival crevice
Organisms that prefer hard tissue colonization,such as S.mutans, S.sanguis and Actinomyces sp. then selectively colonize enamel. Organisms that prefer anaerobic environment such as Prevotella, Porphyromonas and spirochaetes colonize the crevicular tissues. However, the anaerobs do not appear in significant numbers until adolescence. A second phase of bacterial colonization is reached if all teeth are lost as a result of senility. Bacteria that colonize the mouth at this stage are very similar to those in a child before tooth eruption.Introduction of a prosthetic appliance at this stage changes the microbial composition once again. Growth of Candida sp. is particularly increased after the introduction of acrylic dentures.
Chapter 3: Gram-positive cocci Streptococcus: They are gram positive cocci in chains,non-motile,usually possessing surface fibrils.Occasionally capsulated,facultative anaerobs.Variable hemolysis but alpha -hemolysis most common.
They also grow well on most of the non-specific culture medias,as they are not exacting in their nutritional requirements.They commonly appear in culture plates as diffuse spreading colonies without any pigment formation.On gram staining they appear as chains of cocci. They are classified according to different criteria and characteristics. One classification is based on the carbohydrate content of the cell wall,another classification is based on the presence or absence of a cell wall protein known as m-protein.
Mutans group: Cultural characteristics:high,convex,opaque colonies;produce profuse extracellular polysaccharide in sucrose containing media. The main intraoral site is tooth surface and produces dental caries. Salivarius group: Cultural characteristics:large,mucoid colonies on MSA due to production of extracellular fructans. S.vestibularis do not produce extracellular polysaccharide from sucrose;they produce urease and H2O2,which lowers the pH and contributes to salivary peroxidase system. Main intraoral sites are dorsum of tongue and saliva. Anginosus group They are CO2-dependent;form small non-adherent colonies on MSA. Main intraoral site is gingival crevice.They may cause dentoalveolar and endodontic infections.
Mitis group: Cultural characteristics:small,rubbery or non-adherent colonies on MSA. Main intraoral sites are dental plaque,tongue and cheek.They causes dental caries and infective endocarditis.
Anaerobic Streptococci Main species: Peptostreptococcus anaerobius;P.micros;P.magnus. Cultural characteristics:strict anaerobs,slow-growing,usually nonhemolytic. Main intraoral site is teeth,especially carious dentin.They causes periodontal and dentoalveolar abscesses .
Enterococcus Little information is available on the presence of Enterococci in the healthy mouth.They can be isolated from the mouth of immuno- and medically- compromised patients.The most frequently isolated species is E.faecalis , from infected root canals and from periodontal pockets.
Stomatococcus Main species is Stomatococcus mucilagenosus. Cultural characteristics:coagulase-negative,forms large colonies adherent to blood agar surface,facultative anaerobes. It produces an extraoral slime which plays an important role in association of this species with that site. Main intraoral site is tongue,gingival crevice.
Staphylococci They are not isolated in large numbers from oral cavity. They may be associated with plaque samples from subjects with dentures,as well as in immunocompromised patients and individuals suffering from a variety of oral infections.
Chapter 4: Gram positive rods and filaments Actinomyces Main species:A.israelii ,A.gerencseriae, A.odontolyticus, A.naeslundii, A.myeri, A.georgiae. The most important human pathogen is A.israelii They produce sulphur granules.
Cultural characteristics:ferments glucose to give characteristic patterns of short-chain carboxylic acids useful for speciating. They are either strict or facultative anaerob.Main intraoral sites and infections:A.odontolyticus in earliest stages of enamel demineralization and the progression of small carious lesions. A.naeslundi implicated in root surface caries and gingivitis.A.israelii is an opportunistic pathogen causing cervicofacial and ileocaecal actinomycosis.
Granules of Actinomyces
Lactobacillus Main species:L.casei, L.fermentum, L.acidophilus, L.salivarius, L.rhamnosus. Cultural characteristics:catalase negative,microaerophilic;complex nutritional requirements;aciduric;optimum pH 5.5-5.8 Selective medium: Rogosa agar.
Common oral inhabitants,but comprise less than 1% of the oral flora. They are usually associated with dental plaque and advancing front of dental caries. As levels of salivary lactobacilli correlate well with intake of dietary carbohydrates,they are used to detect the cariogenic potential of the diet.
Eubacterium Main species:E.brachy, E.timidum ,E.nodatum, E.saphenum. Cultural characteristics:obligatory anaerobs,characterization is illdefined. Main intraoral sites are dental plaque and calculus;implicated in caries and periodontal disease .
Propionibacterium Cultural characteristics:strict anaerob;produces propionic acid from glucose.
They are associated with dental plaque.They are implicated in root surface caries and dentoalveolar infections, deep layers of infected root canal dentin.
Chapter 5: Gram-negative cocci Neisseria Main species:N.subflava, N.mucosa, N.sicca. Cultural characteristics:asaccharolytic and non-polysaccharide producing,facultative anaerob. Isolated in low numbers from tongue,saliva,oral mucosa and early plaque;rarely associated with disease.
veilonella Main species:V.parvula, V.dispar, V.atypica. Cultural characteristics:strict anaerob,selective medium is Rogosa vancomycin agar. They use lactate produced by other bacteria and raise the pH of plaque,and are thus considered to be beneficial in relation to dental caries.Isolated from most surfaces including tongue,saliva and dental plaque.No association with disease.
Chapter 6: Gram negative rods – facultative anaerobic Haemophilus They are coccobacilli,having a club shaped appearance. Main species:H.parainfluenzae, H.segnis, H.aphrophilus, H.haemolyticus, H.parahaemolyticus. Cultural characteristics:facultative anaerobs,growth enhanced on heated blood agar,requires haemin and NAD for growth.
Main intraoral sites are dental plaque,saliva and mucosa.They are associated with dentoalveolar infections,acute sialadenitis,infective endocarditis.
Actinobacillus Gram negative coccobacilli,microaerophilic or capnophilic. Main species:A.actinomycetemcomitans(serotypes a-e) Cultural characteristics:freshly isolated strains contain fimbriae that are lost on subculture.Produces many virulence factors like leucotoxin,collagenase, protease . Mostly isolated from periodontal pockets and implicated in localized and generalized aggressive periodontitis.
Eikenella Main species:E.corrodens Cultural characteristics:they are dependent on haemin, microaerophilic, produces corroding colonies on blood agar. Main intraoral site is dental plaque.Commonly associated with dentoalveolar abscesses,infective endocarditis,some form of chronic periodontitis.
Capnocytophaga They are CO2 –dependent,gram negative fusiform rods with ‘gliding motility ‘. Main species : C.gingivalis, C.sputigena, C.ochracea, C.granulosa, C.haemolytica .
Cultural characteristics:capnophilic,medium sized colonies with an irregular spreading edge. Mostly isolated from plaque,mucosal surfaces,saliva.Associated with infections in immunocompromised,destructive periodontal disease.
Chapter 7:gram negative rods-obligate anaerobs Porphyromonas They are gram negative pleomorphic rods,non-motile,six serotypes based on capsular polysaccharide(K-antigen),asaccharolytic. Main species:P.gingivalis ,P.endodontalis, P.catoniae.
Cultural characteristics:strict anaerob,require Vit.K and haemin for growth. Isolated intraorally from gingival crevice and subgingival plaque.Associated with chronic periodontitis and dentoalveolar abscess. P.gingivalis is highly virulent producing proteases,a haemolysin,collagendegrading enzymes and cytotoxic metabolites;its capsule is an important virulent attribute,fimbriae helps adhesion.P.endodontalis is mainly recovered from infected root canals.
Prevotella Gram negative pleomorphic rods,non-motile;moderately asaccharolytic, producing acetic,succinic and other acids from glucose. Main species:pigmented species include P.intermedia, P.nigrescens, P.loeshii, P.corporis, P.melaninogenica. Non-pigmented species include:P.buccae, P.oralis, P.oris, P.oulora, P.veroralis, P.dentalis. Cultural characteristics:strict anaerob,usually require Vit.K and haemin for growth. Mostly isolated from periodontal pockets,dental plaque.Implicated in chronic periodontitis and dentoalveolar abscess.
Fusobacterium They are slender,cigar shaped,gram negative rods with rounded ends. Main species:F.nucleatum, F.alocis, F.sulci, F.periodonticum. Cultural characteristics:require rich media for growth and are often asaccharolytic,strict anaerob,usually non-haemolytic.
F.nucleatum can produce ammonia and hydrogen sulphide from cysteine and methionine and is implicated as an odorigenic organism in halitosis. Most commonly isolated from gingival crevice,tonsils.Implicated in periodontal infections,acute ulcerative gingivitis,dentoalveolar abscess.
Leptotrichia They are gram negative filaments with atleast one pointed end. L.buccalis is the main species. Cultural characteristics:strict anaerob,with colonies resembling fusobacteria. Main intraoral site is dental plaque. There is no known disease association.
Wolinella They are gram negative curved bacilli,motile ,flagellated.W.succinogenes is the main species.They are strict anaerob.Mostly isolated from gingival crevice and possible involvement in destructive periodontal disease.
Selenomonas Gram negative curved cells with tufts of flagella. Main species: S.sputigena; S.noxia;S.flueggei;S.inflexi;S.diane.They are strict anaerob.Main intraoral site is gingival crevice.
Treponema Main species:T.denticola, T.macrodentium, T.skoliodontium, T.socranskii, T.maltophilum, T.amylovarum, T.vincentii. Cultural characteristics:strict anaerobs and difficult to culture.Require enriched media with serum. T.denticola is more proteolytic than others and possesses proline aminopeptidase and arginine-specific protease.It also degrades collagen and gelatin.Usually found in gingival crevice.They are closely associated with acute ulcerative gingivitis,destructive periodontal diseases.
Chapter 8: Fungi They form a small part of the oral microflora.
The perfect fungi divide by sexual reproduction and are rarely isolated from the oral cavity but are ocassionally found infecting patients with advanced AIDS.The main perfect fungi causing oral infections are Aspergillus, Geotrichium and Mucor species. The imperfect yeasts divide by asexual reproduction and are commonly found in the mouth.The largest proportion of the fungal microflora is made up of Candida species. Main species:C.albicans, C.glabrata, C.tropicalis, C.krusei, C.parapsilosis, C.guillermondi Candida sp. are distributed evenly throughout the mouth.The most common site of isolation is the dorsum of tongue,dental plaque, intraoral devices such as orthodontic appliances,acrylic dentures etc..Other fungi includes Rhodotorula and Saccharomyces sp.
Chapter 9: Mycoplasma They are pleomorphic microorganisms which possess an outer membrane that is not rigid.They can be grown either on media that are highly enriched with proteins and in presence of CO2 or in tissue culture.
Main species: M.salivarium, M.pneumoniae, M.hominis, M.buccale, M.orale. Isolated from saliva,mucosa,dental plaque and has possible association with salivary gland hypofunction.
Chapter 10: VIRUSES Commonest virus detected in the oral cavity is Herpes simplex.It causes cold sores.It can also remain latent ;it migrates rapidly long the trigeminal nerve to the ganglion where it remains latent until reactivated.
Cytomegalovirus is present in most individuals. Coxsackie virus A have been detected in saliva and oral epithelium.A variety of papilloma viruses have been isolated from the oral cavity associated with small warts.These warts have been implicated with oral cancer, and are common in AIDS patients. Hepatitis and HIV viruses can be found in the oral cavity, especially in saliva,where there presence poses a significant cross-infection threat. Other viruses found in the oral cavity are orthomyxo and paramyxo viruses but usually in association with oral lesions.
Chapter 11: PROTOZOA Entamoeba gingivalis is the most common protozoan,and has been isolated from periodontal tissues,particularly in patients who have received radiotherapy and are taking metronidazole. Trichomonas tenax,a flagellated protozoan, has been isolated from the oral cavity of healthy patients;it may cause salivary gland swellings,particularly in parotid gland. Giardia lamblia has been seen in the oral cavity,but its role and incidence is not known.
Chapter 12: The Oral Ecosystem Ecology is the study of the relationships between living organisms and their environment.The term environment means the total of the physical, chemical and biological characteristics of the surroundings that are potentially available for habitation. Niche is defined as the specific combinations of physical, chemical and biological parameters that are necessary for the survival of a particular organism. The process by which organisms sequentially inhabit an altered environment is known as ecological succession. To deal with the taxonomic diversity bacterial species can be divided on the basis of prevalence into:
Indigenous flora: It comprises those species that are almost always present in high numbers in a particular site.They are compatible with the host and have entered into a stable relationship with the host.They do not compromise the host’s survival.Streptococcus,Actinomyces, Neisseria are examples of the indigenous flora. Supplemental flora: It comprises species that are nearly always present, but in low numbers (
