Oral biofilms and transferable antibiotic resistance

Introduction: The oral cavity 23 Dental plaque 24 Diseases caused by dental biofilms 25 The use of antibiotics to treat periodontal disease 26 Intrinsic biofilm-mediated antibiotic resistance 27 Mechanisms of bacterial-mediated resistance in oral biofilms 28 Resistance found in oral biofilms 30 Mechanisms of gene transfer among oral bacteria 32 Mobile elements involved in the transfer of antibiotic resistance 33 Evidence for horizontal gene transfer of antibiotic resistance in the oral cavity 34 Transformation in the oral cavity 34 Transduction in the oral cavity 36 Conjugation in the oral cavity 36 The effects of antibiotics on horizontal gene transfer within the oral cavity 37 Concluding remarks 38 Acknowledgments 39 References 39 Introduction: The oral cavity The oral cavity is one of the most extensively colonized environments in the human body. This is due to the fact that the oral cavity contains many distinct ecological habitats, such as the tooth surface, both above and below the gingival margin; saliva; and the various mucosal surfaces, such as the surface of the tongue. Also, the oral cavity often comes into contact with a wide variety of growth substrates through the ingestion of different foods. The number of species of bacteria contained in this environment is thought to be between five and six hundred [1,2]. Not all of these species are currently able to be cultivated under laboratory conditions. Researchers have estimated that approximately 10 to 50% of these different species of bacteria are culturable [1,3]. In a recent study, approximately 40% of the bacteria identified by amplification and sequencing of the 16S rRNA gene were novel, and probably represent the species that cannot yet be grown under laboratory conditions [1]. More recent estimates, again based on extensive cloning and sequencing of the 16S rRNA genes, have put this figure at approximately one thousand species [4]. In any one oral cavity, however, the typical amount of bacterial species that will be able to be cultured from a single plaque sample is between twenty and thirty. Therefore, the total number of species present in the sample is likely to be between forty and sixty. Additionally, the species profile is likely to be different for different samples investigated [5]. The majority of bacteria in the oral cavity grow on the surface of the tooth as part of a complex, multispecies biofilm commonly known as dental plaque.