Ecological and genetic determinants of plasmid distribution in Escherichia coli

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...细菌质粒（bacterial plasmids）是毒力因子与抗生素耐药基因的重要载体。然而，目前对于细菌种群中质粒分布的决定因素仍知之甚少。本研究以栖息于半天然草原、抗生素耐药基因携带频率较低的牛群为研究对象，探究了影响大肠杆菌（Escherichia coli）大型质粒多样性与分布的相关因素。尤为关键的是，本研究对细菌宿主的种群遗传结构进行了系统表征。分析结果表明，大肠杆菌种群存在明显的结构分化：不同采样位点与个体间的多样性水平较高，但单个牛宿主体内的多样性水平较低。但即便在同一大肠杆菌基因型内，质粒谱（plasmid profiles）仍存在显著差异。生态与遗传因素均可对质粒分布产生影响：质粒谱受采样位点、大肠杆菌多样性、大肠杆菌基因型以及其他大型质粒的存在与否共同调控。值得注意的是，二十六分之三的大肠杆菌血清型（E. coli serotypes）占观测到的全部无质粒分离株的一半，表明……