Horizontal gene transfer, mediated by conjugative plasmids, is a major driver of the global rise of antibiotic resistance. However, the relative contributions of factors that underlie the spread of plasmids and their roles in conjugation in vivo are unclear. To address this, we investigated the spread of clinical Extended Spectrum Beta-Lactamase (ESBL)-producing plasmids in the absence of antibiotics in vitro and in the mouse intestine. We hypothesised that plasmid properties would be the primary determinants of plasmid spread and that bacterial strain identity would also contribute. We found clinical Escherichia coli strains natively associated with ESBL-plasmids conjugated to three distinct E. coli strains and one Salmonella enterica serovar Typhimurium strain. Final transconjugant frequencies varied across plasmid, donor, and recipient combinations, with qualitative consistency when comparing transfer in vitro and in vivo in mice. In both environments, transconjugant frequencies for these natural strains and plasmids covaried with the presence/absence of transfer genes on ESBL-plasmids and were affected by plasmid incompatibility. By moving ESBL-plasmids out of their native hosts, we showed that donor and recipient strains also modulated transconjugant frequencies. This suggests that plasmid spread in the complex gut environment of animals and humans can be predicted based on in vitro testing and genetic data.

由接合质粒介导的水平基因转移是全球抗生素耐药性上升的主要驱动力。然而，构成质粒传播基础的因素的相对贡献及其在体内结合中的作用尚不清楚。为了解决这个问题，我们在体外和小鼠肠道中调查了在没有抗生素的情况下产生临床超广谱 β-内酰胺酶 (ESBL) 的质粒的传播。我们假设质粒特性将是质粒传播的主要决定因素，并且细菌菌株特性也会有所贡献。我们发现临床大肠杆菌菌株天然与 ESBL 质粒结合，结合三种不同的大肠杆菌菌株和一种沙门氏菌enterica serovar Typhimurium 菌株。最终的转接合子频率因质粒、供体和受体组合而异，在比较小鼠体外和体内转移时具有定性一致性。在这两种环境中，这些天然菌株和质粒的转导结合频率与 ESBL 质粒上转移基因的存在/不存在共变，并受到质粒不相容性的影响。通过将 ESBL 质粒从它们的原生宿主中移出，我们发现供体和受体菌株也调节了转接合频率。这表明可以根据体外测试和遗传数据预测质粒在动物和人类复杂肠道环境中的传播。