A large plasmid, pCERC14, found in an antibiotic resistant commensal Escherichia coli isolate recovered from a healthy adult was sequenced. pCERC14 was 162,926 bp and carried FII-18 and FIB-1 replicons and an F-like transfer region as well as several virulence determinants, some of which are involved in the uptake of iron which would be advantageous for the commensal lifestyle. The plasmid backbone is interrupted in 11 places by complete IS (IS1 (4 copies), IS2 (2), IS629 (2) and single IS100, IS186, ISEc33) and in three places by partial IS copies. The antibiotic resistance genes were found in two IS26-bounded pseudo-compound transposons (PCT). One contained a remnant of a class 1 integron that includes a dfrA5 gene cassette and the sul1 gene conferring resistance to trimethoprim and sulphonamides, respectively. The second, named PTntet(C)-var, contained a 4828 bp DNA segment that includes the tet(C) tetracycline resistance determinant. As tet(C) is relatively rare in E. coli and other Gram-negative bacterial isolates, the structure and evolution of tet(C)-containing PCT in available sequences was examined. The largest identified was PTntet(C), a close relative of PTntet(C)-var, and a potential progenitor for these PCT. Most PCT shared one internal boundary with PTntet(C) but the length of the central tet(C)-containing segment was shorter due to IS26-mediated deletions. The most abundant variant form, previously named Tn6309, was widely distributed and, in a derivative of it, most of the tetA(C) gene has been replaced by the tetA(A) gene presumably by homologous recombination.

在从健康成人回收的抗生素抗性共生大肠杆菌分离物中发现的大质粒 pCERC14被测序。pCERC14 为 162,926 bp，携带 FII-18 和 FIB-1 复制子和 F 样转移区以及几个毒力决定因子，其中一些涉及铁的吸收，这将有利于共生生活方式。质粒骨架在 11 个地方被完整的 IS（IS 1（4 个拷贝）、IS 2（2）、IS 629（2）和单个 IS 100、IS 186、ISEc33）中断，在三个地方被部分 IS 拷贝中断。在两个 IS 26中发现了抗生素抗性基因有界伪复合转座子 (PCT)。其中一个包含 1 类整合子的残余物，其中包括dfrA5基因盒和分别赋予甲氧苄啶和磺胺类药物抗性的sul1基因。第二个称为 PTn tet (C)-var，包含 4828 bp DNA 片段，其中包括tet (C) 四环素抗性决定簇。由于tet (C) 在大肠杆菌和其他革兰氏阴性细菌分离物中相对罕见，因此检查了可用序列中含有tet (C) 的 PCT的结构和进化。确定最大的是PTN TET（C），PTN的近亲TET(C)-var，以及这些 PCT 的潜在祖先。大多数 PCT 与 PTn tet (C)共享一个内部边界，但由于 IS 26介导的缺失，包含中央tet (C) 的片段的长度较短。最丰富的变体形式，以前称为 Tn 6309，分布广泛，在它的一个衍生物中，大部分tetA (C) 基因已被tetA (A) 基因取代，推测是通过同源重组。