Oral Microbiology and Rational Use of Antibiotics

Philippe Hennet France

1. MICROBIOLOGY OF THE ORAL CAVITY

Bacteria are normal inhabitants of the digestive tract, the oral cavity being the first part of it. From the normal flora known as the indigenous or endogenous flora, specific bacteria may develop due to a change in the micro-environmental conditions and set up an opportunistic infection. Oral health is an equilibrium between endogenous bacteria and the oral defense system.

Oral defense is mainly based on physical barriers (keratinized epithelium, mucous production, salivary flush), production of chemical compounds (salivary enzymes and antibacterials, gingival fluid secretions, etc.), and inflammatory reaction. It is estimated that 100 billion bacteria from all oral surfaces are shed daily in the saliva. The total plaque flora constitutes about five percent of the salivary flora. About 300 different species can be isolated from the dental plaque alone. One mg of dental plaque contains about 10 million bacteria. The flora of clinically healthy gingiva is mainly composed of aerobic and facultative anaerobic bacteria. Subgingival flora associated with periodontitis is predominantly anaerobic: Porphyromonas spp. (previously asaccharolytic black-pigmented Bacteroides), Prevotella spp. (previously saccharolytic Bacteroides), Peptostreptococcus spp., Fusobacterium spp. and Spirochetes. High levels of Porphyromonas spp., particularly P. gingivalis, and spirochetes are consistently associated with progressive periodontitis in the dog. Other oral infectious diseases include caries, periapical infection, odontogenic infections, osteomyelitis and stomatitis.

2. RATIONAL USE OF ANTIMICROBIALS

Antiseptics

Antiseptics can be used prior to any oral surgery to reduce the bacterial load. They are also part of the prevention of plaque accumulation on tooth surfaces (plaque retardant agents), combined whenever possible with tooth brushing. The most effective plaque retardant agent to date is chlorhexidine. It is incorporated in various oral solutions, gels, and toothpastes. Because of possible interactions with other chemical compounds, its effectiveness should be assessed in vivo prior to marketing commercial formulations.

Antibiotics and Antimicrobials

Antibiotic Prophylaxis. A specific protocol should apply to animals at risk of developing systemic diseases subsequent to bacteremia. They include immunocompromised animals, animals with organic or metabolic failure, animals with heart disease and possibly animals with a prosthetic joint. Wound contamination may occur when healthy tissue is exposed to the oral flora during dental treatment. This is the case when crown height reduction and partial vital pulpectomy is performed as well as when healthy oral mucosa or bone is exposed during periodontal or oral surgery. An injectable antibiotic such as amoxicillin or ampicillin can be used at a dosage of 20�25 mg/kg IV, IM 30 minutes before the procedure then 10�12.5 mg/kg IV, IM four hours after initial dose.

Antibiotic Therapy. Choice of the antibiotic must be based on knowledge of the predominant bacterial flora associated with the disease process, culture results (if specific anaerobic sampling and culturing techniques can be used), site of infection, and physiologic status of the animal.

Without any doubt, periodontics is the branch of dentistry where antimicrobials are the most widely used and misused. It should be remembered that treatment of periodontal disease is scaling, root planing, polishing, and possibly dental extractions and periodontal surgery. Antibiotics should be use with discrimination because they may have potential side effects (superinfections, bacterial resistance, allergic, and toxic reactions, etc.) and they are unable to cure oral diseases when used alone. Systemic antibiotics may be helpful when dealing with a maxillo-facial cellulitis caused by pulpal infection. If a single-visit treatment is performed in such a case, antibiotic therapy should be used. Replantation of exarticulated and luxated teeth is associated with high risk of inflammatory root resorption. It has been shown in dogs and in monkeys that after systemic antibiotic treatment at the time of replantation, there was no inflammatory root resorption or there were shallower resorptive cavities without inflammatory cells.

Antibiotic therapy might be useful as an adjunct to periodontal therapy. Recently, studies in humans and dogs have focused on the beneficial effect of specific antibiotic therapy on periodontal tissue healing after treatment. Antibiotics studied include metronidazole, tinidazole, spiramycin and spiramycin-metronidazole, Metronidazole-Amoxicillin and Clindamycin. Nitroimidazoles, such are metronidazole and tinidazole have been thoroughly studied in humans and in dogs and seem so far the more promising antibacterial to use as an adjunct to periodontal therapy. More recent development in periodontics is the use of controlled-release localized administration of antibiotics. To date, three commercial products respectively containing metronidazole, doxycycline and minocycline are found. Only the sustained release doxycycline polymer is registered and marketed for veterinary use to date (Doxyrobe, Pharmacia Co.).

Antibiotics Most Commonly Used For Oro-Dental Diseases

 Amoxicillin: 10 mg/kg q12h

 Amoxicillin-Clavulanate: 12.5 mg/kg q12h

 Clindamycin: 5.5 mg/kg q12h or 11 mg/kg q24h

 Doxycycline: 10 mg/kg q24h

 Metronidazole: 15-20 mg /kg q12h

 Metronidazole-Spiramycin: 12.5 �16 mg/kg (Metronidazole) + 75,000-100,000 UI /kg (Spiramycin)