Infectious Diseases

 

As has been discussed, most members of the indigenous flora are anaerobes. Anaerobes are likely to penetrate epithelium and given the relatively large surface area of combined periodontal pockets, more anaerobes are likely to enter the underlying connective tissue than facultative organisms. It has been previously claimed by Loesche and others. (1997) that because of the high pC>2 and Eh1 of these tissues, anaerobes are contained and rarely appear in the blood stream. Indeed, these organisms find the highly aerobic host cells so unfavourable that they rarely survive to enter the bloodstream. However, because most of these anaerobes are Gram-negative, their lipopolysaccharide can initiate events that may increase the circulating levels of cytokines, with possible adverse effects for the host (Beck and others 1998).

Despite it being generally regarded that blood is a highly oxygenated medium in which oral anaerobes cannot survive for any length of time (Loesche and others 1995), it should be realised however that organisms reaching the blood from an oral site will have been transported in the bloodstream to peripheral sites of the body within 1 minute (Roberts and others 1992). Furthermore, some of the strictest anaerobes e.g. Clostridium haemolyticum are not killed when exposed to atmospheric oxygen on the laboratory bench top until after 10 minutes or longer. Moderate obligate anaerobes tolerate oxygen for much longer times. Anaerobes such as Bacteroides fragilis also have enzyme such as catalase and superoxide dismutase that are protective against toxic oxygen reaction products. Therefore anaerobes are probably better able to survive in the bloodstream than previously thought. Scattered among the anaerobic species among the indigenous flora are various facultative species (Loesche and others 1995).

These lack the overt virulence factors of the classic pathogens. More of these facultative species, such as the Streptococci and Actinomyces are found in the oral cavity and in dental plaque (where air can pass) than anywhere else in the body. Many of the  facultative species in supragingival plaque, when they breach the physical barrier of the epithelium, are not susceptible to the electrical barrier created by the high tissue oxidation-reduction potentials and if they were not quickly scavenged by tissue monocytes would survive in the bloodstream eventually gaining access to the peripheral circulation. Thus facultative species such as S.sangius and S.faecalis are more likely to survive within the tissue.