Infections from oral cavity can arise from odontogenic source (common in adults), from tonsil and lymphoid sources (common in children). The microbiological profile of infections arising from either of these sources are different calling for a difference in the treatment modality followed.
Odontogenic infections arise as a result of dental caries (advanced) or from periodontal disease. The evolution of infections from teeth occurs as follows: Dental diseases gives rise to pulpitis which could progress to periapical abscess which could ultimately spread through bone and soft tissues to involve deeper structures.
Other potential non odontogenic causes of oral cavity infections are:
Salivary gland infections – common in patients with dehydration
Lymph node abscess
Post operative infections
Dangers of oral cavity infections include:
Involvement of orbit & brain
Endocarditis in patients with cardiac prosthesis (valves)
Spread of infections to retropharyngeal space
Anatomical aspects of oral cavity infection:
Infections involving oral cavity usually spread via pathways of least resistance. These pathways of spread are decided by various spaces present in the neck. The neck spaces are anatomically created by superficial, middle and deep cervical facia and their attachements. These various neck spaces are interconnected and hence infections from one space can freely transgress to other spaces too.
Three posterior pharyngeal spaces are present. They include:
Retropharyngeal space – Extends from the skull base to the upper mediastinum. It contains the node of Rouviere which is a lymph node which involutes at the age of 6. Abscess involving this space can rupture into the Danger space which lies posteriorly
Danger space – Lies just behind the retropharyngeal space and extends up to the inferior mediastinum
Prevertebral space – Lies posterior to the Danger space. It extends up to the coccyx. Its posterior boundary is formed by the vertebral body and its covering prevertebral fascia.
Lateral pharyngeal space
Visceral vascular space – This space extends from the skull base to the mediastinum. It contains all the three layers of deep cervical fascia. Important components of this space include:
Parapharyngeal space on either side of pharynx:
This space is also known as pterygomaxillary space. It is divided into anterior and posterior portions. The anterior component of this space contains parapharyngeal fat and tonsillar fossa. It does'nt have any boundaries and can access other spaces also. The posterior component of parapharyngeal space is a neurovascular space.
In all patients with oral cavity infections the threat of mediastinitis should always be considered. X-ray soft tissue neck is a useful screening tool. All these patients should under go CT scan imaging.
Bacteriology of odontogenic infections:
The type of bacteria found in odontogenic infections are normal commensals of the oral cavity. Odontogenic infections are commonly polymicorbial and the invasiveness of the infecting organism is determined by various factors. These normal commensals reside within biofilms present in the oral cavity. These biofilms are composed of polysaccharides and it provides the microbes protective environment to reside and proliferate. Antibiotics have not known to penetrate these biofilms.
Majority of normal bacterial flora of oral cavity are anaerobes. The following normal commensal organisms have been cultured from the oral cavity mucosa:
In addition to the above mentioned organism there are certain specific bacteria colonizing specific areas of the oral cavity.
Streptococcus salivarius and Veillonella colonizes the tongue, buccal mucosa and saliva.
Streptococcus sanguinis, mutans, mitis, Actinomyces viscosus have been found to colonize surface of dentition.
Anaerobes like Fusobacterium, porphyromonas, provotella and spirochetes have been known to colonize the gingival crevises.
Alterations in these bacterial flora can occur in the following scenario:
Use of tobacco
Decidious teeth eruption
Plaque formation predisoposes to odontoenic infections. Plaque is nothing by supragingival biofilm. It can predispose to dental caries due to the presence of bacterial byproducts present within it. These plaques contain mainly gram negative anaerobic organism. Bacteriologically dental caries and periodontitis differ. Streptococcus mutans has been clearly implicated in dental caries. In gingivitis the following organims are common i.e. Provetella intermedia, peptostreptococcus and capnocytophaga.
Patients with deblitating diseases have Methicillin resistant staphylococcus aureus and facultative gram negative bacilli. This aspect should be taken into consideration for the purpose of prescribing antibiotics to these patients.
Non odontogenic oral infections:
The pathogens involved in this category are different from that of odontogenic oral infections. They include:
Herpes simplex virus
Fungal infections with Candida, Aspergillus are common in patients with HIV infections.
Rapid eradication of infection in order to decrease the degree of tissue destruction
Decrease / avoiding the inappropriate antibiotic usage. This needs to be evaluated with relevant antibiotic intake history from the patient. Drug resistance is common in these patients.
While selecting the appropriate antibiotic depending on culture and sensitivity report the drug with the narrowest spectrum should be choosen.
Role of Beta lactam antibiotics:
Drugs belonging to this group inhibits bacterial cell wall synthesis by preferentially binding to cell wall synthesising protein. This binding irreversibly destroys cell wall by the production of Hydroxyl radicals. Bacterial resistance to this group of drugs is due to the production of beta lactamase enzymes.
Penicillins belong to the primary beta lactam group. It can be divided into 5 groups.
Natural penicillins – Penicillin G and Penicillin V
First generation penicillin – Nafcillin, oxacillin, cloxacillin and dicloxacillin resistant to penicillinase
Second generation penicillin – Ampicillin and amoxycillin
Third generation penicillin – Ticarcillin also effective against gram negative bacteria
Fourth generation penicillin – Pipercillin
Beta lactamase inhibitors:
Bacteria circumvent the deleterious effects of beta lactum antibiotics by secreting betalactamase enzymes. Co administration of beta lactam antibiotics along with clavulenate and sulbactum which are inhibitors of beta lactamase enzyme will potentiate the effects of the drug.
Cephalosporins are commonly used beta lactam antibiotic. They are active against a broad spectrum of organim and are easy to administer. Drugs belonging to this group are active against gram positive bacteria and are divided into various generations depending on their spectrum of action and gram negative bactericidal activity.
First generation cephalosporin- Cefazoline intravenous drug commonly used. Its antimicrobial spectrum does not cover bacteroids and hence should not be used when bacteroids are suspected to be the cause for infection. It is also inactive against gram negative organism like pseudomonas, proteus and enterobacter. First generation oral cephalosporin include cephalexin, cefadroxyl and cephadrine.
Second generation cephalosporin – Cefaclor, cefprozil, cefuroxime and cefoxitin. This group has broader gram negative coverage with less gram positive activity. Cefuroxime is the only drug beloning to this group capable of penetrating the blood brain barrier and is hence considered to be the choice in patients with threatened intracranial complications due to oral infections.
Third generation cephalosporin – Ceftriaxone, cefotaxime are classic examples of drugs belonging to this group. Drugs belonging to this group demonstrate broad coverage, high potency and low toxicity. Drugs belonging to this group are very active against penumococci. Its activity against gram positive organism is less than that of first generation cephalosporin. Drugs belonging to this group are resistant to common beta lactamases produced by gram negative pathogens and hence is very useful in patients with mixed infections. Drugs belonging to this group have been subdivided into two groups depending on their action on pseudomonas organism. The first group which include ceftaxine and ceftriaxone are virtually ineffective against pseudomonas organism while drugs belonging to the next group ceftazidime is active against pseudomonas organism.
Fourth generation cephalosporin – Cefepime is the classic example of drug beloning to this group. Drugs belonging to this group show enhanced penetration of gram negative cell wall and resistance to beta lactamase produced by gram negative bacteria. Majority of enterobacteria are susceptible to cefepime.
Fifth generation cephalosporin – Cetobiprole belongs to this group. It is not freely available at present. The major advantage of this drug is its enhanced activity against gram negative bacteria.
Carbapenems – Have the widest bacterial spectral coverage. Drugs belonging to this group are highly resistant to beta lactamases produced by gram negative organism. Drugs belonging to this group are Ertapenem, imipenem – cilastatin, meropenem and doripenem. Drugs belonging to this group are highly active against gram positive organisms, gram negative organims including enterococci.
Aminoglycosides- Are broad spectrum antibiotics which have effects against both gram positive and gram negative organism. Drugs belonging to this group include gentamycin, amikacin, stroptomycin etc. Drugs belonging to this group are extermely toxic and must be used with caution.
Clindamycin – is very useful in infections involving bacteriods. Since bacteroids play a vital role in oral cavity infections this drug could of use in this scenario. It is also very effective against anaerobes.
Metronidazole- Is very useful in treating oral cavity infections because of its effect on anerobes. It is very useful in patients with vincent's angina.