ABSTRACT
Bacteria can be classified by the type of oxidation-reduction reactions used to generate energy needed for growth and multiplication. Anaerobic bacteria are grouped as facultative, microaerophilic, or obligate anaerobes, depending on their degree of oxygen tolerance. Facultative anaerobes tolerate the presence or absence of oxygen, and microaerophils tolerate only no or low concentrations of oxygen. Obligate anaerobes, however, cannot survive long even when exposed to very low concentrations of oxygen. Indeed, obligate anaerobes tolerate only an environment with an oxidizing capacity (as measured by the redox potential) lower than would occur following total removal of oxygen; these very low redox potentials result from the additional presence of reducing agents, such as devitalized tissue in vivo. Similarly, devitalized tissue (e.g., chopped meat or liver) or reducing agents (cysteine or thioglycollate) are used in culture systems to lower the redox potential sufficiently to permit growth of obligate anaerobes in vitro. Obligate anaerobes are the predominant constituents of the normal microflora of the gingival crevice. The crevicular microflora is a complex ecosystem composed
of several hundred different bacterial species. Its bacterial density approximates that of solid packed bacteria, as are found in colonies growing on an agar plate (i.e., 1012 colony-forming units [CFU]/gram). The crevicular microflora is normally predominantly gram-positive and the predominant anaerobic bacterial species is Actinomyces; but in the presence of periodontitis, the gingival crevice deepens as the epidermal dentine junction recedes toward the tooth apex. The bacterial microflora in the abnormal periodontal pocket becomes predominantly gram-negative, and the predominant anaerobic bacterial species are Porphyromonas, Prevotella, Bacteroides, and Fusobacterium species [1]. Saliva that bathes these surfaces contains gingival crevice microorganisms in addition to organisms that colonize the nasopharynx, tongue, and buccal mucosa, such as viridans streptococci and known aerobic pulmonary pathogens, such as Streptococcus pneumoniae andHemophilus influenzae.
