Microbiology of Odontogenic Infections: Aerobic and Anaerobic bacteria predominant in infections

Microbiology of Odontogenic Infections; Aerobic and Anaerobic bacteria predominant in infections The bacteria that cause Infection are most commonly part of a indigenous bacteria that normally leave on or in the  host, for example bacteria of plaque, found on mucosal surface, and those found in in in gingival sulcus.

 These bacteria are primarily aerobic gram positive cocci, anaerobic gram positive cocci and anaerobic gram negative rods .

These bacteria gain access to  underlying tissue through a necrotic dental pupl or through  deep periodontal pocket and cause odontogenic infection.

Almost all odontogenic infections are caused by multiple bacteria. 

Infection caused by aerobic bacteria alone account for 6% of all odontogenic infections.

Anaerobic bacteria are found in 44% percent of odontogenic infections.

Infections caused by mixed i.e. both aerobic and anaerobic bacteria comprise 50% of all odontogenic infections.

The predominant aerobic bacteria in odontogenic infections are Streptococcus milleri group(found in 65% of cases),  which consists of three members of Streptococcus viridans group of Bacteria; S. anginosus, S. intermedius, S. constellatus.

The anaerobic bacteria found in odontogenic infection include an even greater variety of species. Two main groups however  predominate.

 The anaerobic gram positive cocci are found in 65% of cases.  These are anaerobic Streptococcus and Peptostreptococcus.

Microbiology of Odontogenic Infections

Gram Negative anaerobic rods are cultured in about three-quarters of infections.  The Prevortella and Porphyromonas species are found in in 75% of these and fusobacterium organisms are present in more than 50%.

 Early infections appearing initially as a cellulitis may be characterized as predominantly aerobic streptococcal infections and late chronic abscess may be characterized as anaerobic infections. 

Mechanism of infection\Pathogenesis of Odontogenic Infections

After initial inoculation into deeper tissue the facultative S. milleri  group organism can synthesise Hyaluronidase which allows the infecting organism to spread through connective tissue initiating the cellulitis stages of infection.

Metabolic byproducts from the Streptococcus create a favourable environment for the growth of anaerobic by :  release of essential nutrients lowered PH in the tissue and consumption of local oxygen supplies so that  anaerobic bacteria are able to grow and as the local oxidation reduction potential is lowered for the anaerobic bacteria predominant and cause liquefaction necrosis of tissue by their synthesis of collagenase.

As collagen is broken down and inviting white blood cell necrose and lyse, microabscess form and may coalesce into a clinically recognisable abscess.

 In the abscess stays in aerobic bacteria predominant and may eventually become the only organism found in culture.

(For comparison of different stages of infection; inoculation, cellulitis and abscess, Click here)

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