Bacterial plasmids in the oral and endodontic microflora

Autor: Don B. Clewell, Christine M. Sedgley
Rok vydání: 2004
Předmět:
Zdroj: Endodontic Topics. 9:37-51
ISSN: 1601-1546
1601-1538
Popis: Bacterial plasmids typically represent covalently closed circular, double-stranded, supercoiled DNA molecules that replicate independently of chromosomal DNA. Plasmids are frequently not essential to the bacterial host, but can confer traits facilitating survival under atypical conditions e.g. resistance to antibiotics and heavy metals. Plasmids have been identified in clinical and environmental bacteria from all over the world, and range in size from ∼1 to >200 kb. Their copy number in the cell can range from one or two copies per chromosome, to well over 30; the number is usually characteristic for the particular plasmid. Clinical strains of Enterococcus faecalis, a species commonly associated with root canal infections, can carry as many as six co-resident plasmids with different sizes and copy numbers. In part because of their ability to replicate autonomously, plasmids are used as tools or shuttle vectors in basic molecular biological research. Many plasmids can transfer copies of themselves from one bacterial cell to another by a process called conjugation. In some cases, small peptides called pheromones act as mating signals in this process. Conjugative plasmids that make use of pheromones have been identified previously in E. faecalis and the related plasmids tend to exhibit a narrow host range. Conjugative plasmids in E. faecalis that do not make use of pheromones usually have a much broader host range. Pheromone-responding plasmids in E. faecalis can carry genes relating to antibiotic resistance as well as virulence traits. In general, plasmids are capable of adaptability and stable maintenance in a wide spectrum of bacterial hosts. The potential role of plasmids in oral and endodontic microbiology is discussed.
Databáze: OpenAIRE
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