Normal oral flora
Publisher Summary
Human mouth contains a wide range of sites with different environmental characteristics; the oral flora consists of a complex mixture of microbial species, which include bacteria, mycoplasma, fungi, and protozoa. The mouth consists of a number of ecological niches that are colonized by a characteristic mixture of microorganisms. The main ecological areas of the mouth are: (1) the mucosa of the lips, cheeks, and palate; (2) the tongue; (3) the tooth surfaces—above and below the gingival margin; (4) saliva; (5) the tonsillar area; and (6) dentures, if present. Saliva, although widely used as the main sample in studying the oral microbial flora, does not give an accurate qualitative or quantitative assessment of any particular part of the mouth, and is best regarded as representing the overflow of microorganisms from the other oral sites. This chapter discusses the problems that are associated with qualitative and quantitative investigations of the oral microbial 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 |
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