Normal oral flora

Chapter 2

Normal oral flora

Since the human mouth contains a wide range of sites with different environmental characteristics, it is not surprising that the oral flora consists of a complex mixture of microbial species which include bacteria, mycoplasma, fungi and protozoa. It is not possible in this short book to discuss individual microbial species in detail and, therefore, only the relevant features of the more important members of the oral microflora (selected on the basis of numerical dominance and/or relation to disease) are given. Other microbial characteristics, e.g. factors related to pathogenicity, will be presented in later chapters when specific diseases are discussed. The information is presented in a tabular format (Table 2.1) so that students can refer easily to the appropriate section when they encounter a species with which they are unfamiliar.

Table 2.1

Characteristics of the main microorganisms present in the oral commensal microflora

Genus and main characteristics Main species Cultural characteristics Main intraoral sites/Related infections
Streptococcus      
Gram-positive cocci in chains, non-motile, usually possess surface fibrils, occasionally capsulate. (Note: The term Strep. viridans has been loosely applied as a collective name for α-haemolytic oral streptococci)   Facultative anaerobes, variable haemolysis, but α most common. Selective medium, mitis salivarius agar (MSA)  
  Strep. sanguis Small rubbery colonies on MSA, firmly attached to agar surface Mainly dental plaque/Infective endocarditis, dental caries? and aphthous ulceration?
  Strep. oralis Variable colonial morphology similar to Strep. sanguis or small, soft and non-adherent Tongue, cheek, plaque and saliva/Infective endocarditis
  Strep. mitis Small non-adherent colonies on MSA Dental plaque/None
  Strep. mutans High convex, opaque colonies; extracellular polysaccharide from sucrose. Selective medium MSA + bacitracin; genetically heterogeneous with six species Tooth surface/Dental caries
  Strep. salivarius Large mucoid colonies on MSA Dorsum of tongue and saliva/None
  Strep. milleri CO2dependent; small non-adherent colonies on MSA. Selective medium contains sulphonamide Gingival crevice/Dentoalveolar and endodontic infections
Anaerobic streptococcus      
Small Gram-positive cocci in chains

Strict anaerobes, slowly growing, usually non-haemolytic Sub-gingival plaque/Dentoalveolar infections Lactobacillus       Gram-positive bacilli, catalase negative Microaerophilic; complex nutritional requirements; aciduric; optimal pH 5.5–5.8. Selective medium, Rogosa agar, with low pH due to acetic acid Dental plaque usually in small numbers/Extension of dental caries especially into dentine Actinomyces       Gram-positive bacilli and filaments. Non-motile A. israelii Microaerophilic strict anaerobe, ‘molar’ tooth colony on blood agar Dental plaque and tonsillar crypts/Actinomycosis and dental calculus formation   A. naeslundii Facultative anaerobe     A. viscosus Facultative anaerobe with requirement for CO2 Dental plaque/Root surface caries and calculus formation   A. odontolyticus Facultative anaerobe; reddish-brown centre to colonies Dental plaque/Extension of caries into dentine Arachnia       Gram-positive pleomorphic bacilli A. propionica Strict anaerobe with similar colonial morphology to A. israelii Dental plaque/Carious dentine, necrotic dental pulp, and chronic periodontitis? Eubacterium       Pleomorphic Gram-positive rods or filaments Strict anaerobes, characterization ill defined Dental plaque/Calculus, carious dentine, necrotic pulp and chronic periodontitis? Bacterionema       Gram-positive pleomorphic filaments attached to a rectangular rod shaped body; ‘whip handle’ appearance B. matruchotii Usually facultative anaerobe; some strains strictly anaerobic Dental plaque/Dental calculus formation Propionibacteria       Gram-positive bacilli P. acnes Strict anaerobe, with white colonies surrounded with dark zone on blood agar Dental plaque/Dentoalveolar infections? Rothia Gram-positive branching filaments R. dentocariosa Usually strict aerobe, with white pigmented colonies Saliva and dental plaque/None Bifidobacterium       Gram-positive bacilli B. dentium Strict anaerobe Dental plaque/None Micrococcus + Staphylococcus       Gram-positive cocci, catalase positive M. mucilagenosus Staph. aureus
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Mar 12, 2016 | Posted by in General Dentistry | Comments Off on Normal oral flora
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