Zhao Jing-Yi, Zhao Shu-Mei, Mu Xiao-Dong, Xiao Zijun
FEMS Microbiol Lett. 2017 Apr 1;364(8). doi: 10.1093/femsle/fnw295.
Three qnrS2-containing isolates of Pseudoalteromonas and Shewanella were collected from the seawater samples of Qingdao in China during 2014. They displayed resistance to ampicillin, ciprofloxacin, kanamycin, nalidixic acid and sulfamethoxazole. The qnrS2 genes were identified in the chromosomes of Pseudoalteromonas strains E8 and S16, and in a 140-kb plasmid in Shewanella strain S14, respectively. In addition, two copies of qnrS2 were identified in the strain E8. Sequence analyses revealed that there was an identical DNA segment located in the downstream of qnrS2 in strain S14 and E8, coding for a TetR transcriptional regulator, two putative integrases and a hypothetical protein. However, different genetic structures were identified in the upstream sequences: the terB gene associated with tellurite resistance in the strain S14, and a putative integron with dfrA6 and aadA13 gene cassettes or the Tn7-related gene complex tnsABC in the strain E8. In Pseudoalteromonas strain S16, qnrS2 was bracketed by the endonuclease I and III genes, and the electron transport complex rsxCDGE was located in the upstream sequences. This is the first report of two copies of the qnrS2 gene existing in one bacterial chromosome, and also the first identification of qnrS2 in Shewanella.
2014年期间，从中国青岛海水样本中收集到3株含有qnrS2的假交替单胞菌属和希瓦氏菌属菌株。它们对氨苄西林、环丙沙星、卡那霉素、萘啶酸和磺胺甲恶唑具有抗性。qnrS2基因分别在假交替单胞菌属菌株E8和S16的染色体中以及希瓦氏菌属菌株S14的一个140 kb质粒中被鉴定出来。此外，在菌株E8中鉴定出两个qnrS2拷贝。序列分析表明，菌株S14和E8中qnrS2下游存在一个相同的DNA片段，编码一个TetR转录调节因子、两个假定的整合酶和一个假定蛋白。然而，在上游序列中鉴定出不同的基因结构：菌株S14中与亚碲酸盐抗性相关的terB基因，以及菌株E8中带有dfrA6和aadA13基因盒的假定整合子或Tn7相关基因复合体tnsABC。在假交替单胞菌属菌株S16中，qnrS2被内切酶I和III基因包围，电子传递复合体rsxCDGE位于上游序列中。这是首次报道在一个细菌染色体中存在两个qnrS2基因拷贝，也是首次在希瓦氏菌属中鉴定出qnrS2。
