Conjugative transposons are able to move from one bacterial cell to another by a process requiring cell-to-cell contact. Such elements have been found in many bacterial genera but are particularly common among the Gram-positive streptococci and enterococci. They move via an excision/insertion process that involves a non-replicative circular DNA intermediate possessing plasmid-like conjugative properties. Some exhibit a relatively low level of target-site specificity, whereas others can be very specific. The transposons commonly carry antibiotic resistance determinants and, at least in some species (e.g. Streptococcus pneumoniae and Streptococcus pyogenes), are probably more responsible for the dissemination of these genes than plasmids. Anaerobic, Gram-negative Bacteroides strains are also known to carry non-plasmid resistance elements, and certain tetracycline-resistance transposons in this group exhibit drug-inducible transfer. Some strains of lactococci carry conjugative transposons with determinants for nisin production and sucrose metabolism. For recent reviews of these elements see Clewell and Flannagan (1993), Clewell, Flannagan, and Jaworski (1995), Scott and Churchward (1995), and Salyers et al. (1995).
KeywordsResistance Determinant Conjugative Transfer Conjugative Plasmid Nisin Production Target Core
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