title: Ecological and genetic determinants of plasmid distribution in Escherichia coli.
abstract: Bacterial plasmids are important carriers of virulence and antibiotic resistance genes. Nevertheless, little is known of the determinants of plasmid distribution in bacterial populations. Here the factors affecting the diversity and distribution of the large plasmids of Escherichia coli were explored in cattle grazing on semi-natural grassland, a set of populations with low frequencies of antibiotic resistance genes. Critically, the population genetic structure of bacterial hosts was chararacterized. This revealed structured E. coli populations with high diversity between sites and individuals but low diversity within cattle hosts. Plasmid profiles, however, varied considerably within the same E. coli genotype. Both ecological and genetic factors affected plasmid distribution: plasmid profiles were affected by site, E. coli diversity, E. coli genotype and the presence of other large plasmids. Notably 3/26 E. coli serotypes accounted for half the observed plasmid-free isolates indicating that within species variation can substantially affect carriage of the major conjugative plasmids. The observed population structure suggest that most of the opportunities for within species plasmid transfer occur between different individuals of the same genotype and support recent experimental work indicating that plasmid-host coevolution, and epistatic interactions on fitness costs are likely to be important in determining occupancy.
authors.affiliation: School of Biological Science, Royal Holloway University of London, Egham, Surrey, TW20 0EX, UK.
authors.forename: Frances
authors.initials: F
authors.lastname: Medaney
authors.affiliation: Specialist Scientific Support Department, Animal and Plant Health Agency, APHA Weybridge, Addlestone, Surrey, KT15 3NB, UK.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Ellis
authors.affiliation: School of Biological Science, Royal Holloway University of London, Egham, Surrey, TW20 0EX, UK.|University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, UK.
authors.forename: Ben
authors.initials: B
authors.lastname: Raymond
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002417:Cattle; D002418:Cattle Diseases / Q000382:microbiology*; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000145:classification / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity; D004927:Escherichia coli Infections / Q000382:microbiology / Q000662:veterinary*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D005838:Genotype; D010957:Plasmids / Q000235:genetics* / Q000378:metabolism; D014774:Virulence
chemical_list: D000900:Anti-Bacterial Agents; D029968:Escherichia coli Proteins