Sumrall Eric T, Gallo Elizabeth B, Aboderin Aaron Oladipo, Lamikanra Adebayo, Okeke Iruka N
Department of Biology, Haverford College, Haverford, Pennsylvania, United States of America.
Department of Medical Microbiology and Parasitology, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria.
PLoS One. 2014 Oct 23;9(10):e110279. doi: 10.1371/journal.pone.0110279. eCollection 2014.
The plasmid-encoded quinolone resistance gene qnrS1 was recently found to be commonly associated with ciprofloxacin resistance in Nigeria. We mapped the qnrS1 gene from an Escherichia coli isolate obtained in Nigeria to a 43.5 Kb IncX2 plasmid. The plasmid, pEBG1, was sufficient to confer ciprofloxacin non-susceptibility, as well as tetracycline and trimethoprim resistance, on E. coli K-12. Deletion analysis confirmed that qnrS1 accounted for all the ciprofloxacin non-suceptibility conferred by pEBG1 and tetracycline and trimethoprim resistance could be attributed to tetAR and dfrA14 genes respectively. While it contained a complete IncX conjugation system, pEBG1 was not self-transmissible likely due to an IS3 element inserted between the pilX5 and pilX6 genes. The plasmid was however efficiently mobilizable. pEBG1 was most similar to another qnrS1-bearing IncX2 plasmid from Nigeria, but both plasmids acquired qnrS1 independently and differ in their content of other resistance genes. Screening qnrS1-positive isolates from other individuals in Nigeria revealed that they carried neither pEBG1 nor pNGX2-QnrS1 but that IncX plasmids were prevalent. This study demonstrates that the IncX backbone is a flexible platform that has contributed to qnrS1 dissemination in Nigeria.
质粒编码的喹诺酮抗性基因qnrS1最近被发现与尼日利亚的环丙沙星抗性普遍相关。我们将从尼日利亚获得的一株大肠杆菌分离株中的qnrS1基因定位到一个43.5 Kb的IncX2质粒上。该质粒pEBG1足以使大肠杆菌K-12对环丙沙星不敏感，同时对四环素和甲氧苄啶产生抗性。缺失分析证实，qnrS1导致了pEBG1赋予的所有环丙沙星不敏感性，而四环素和甲氧苄啶抗性分别可归因于tetAR和dfrA14基因。虽然pEBG1包含一个完整的IncX接合系统，但由于在pilX5和pilX6基因之间插入了一个IS3元件，它不能自我传递。然而，该质粒可以高效地被转移。pEBG1与来自尼日利亚的另一个携带qnrS1的IncX2质粒最为相似，但这两个质粒独立获得了qnrS1且它们的其他抗性基因含量不同。对尼日利亚其他个体的qnrS1阳性分离株进行筛选发现，它们既不携带pEBG1也不携带pNGX2-QnrS1，但IncX质粒很普遍。这项研究表明，IncX主干是一个灵活的平台，它促进了qnrS1在尼日利亚的传播。
