College of Veterinary Medicine, China Agricultural University, Beijing 100193, China.
Department of Gastroenterology, the fourth Medical Center of PLA General Hospital, 100048, China.
Sci Total Environ. 2022 Jun 20;826:154010. doi: 10.1016/j.scitotenv.2022.154010. Epub 2022 Feb 23.
Mobile tigecycline-resistance gene tet(X) variants have emerged as diverse pathogens from animal, human as well as their associated environments, which could potentially threaten public health. The insertion sequence, ISCR2, carries tet(X4) for horizontal transfer by rolling-cycle (RC) transposition. However, the diversity of ISCR2 and tet(X4) isolated from different sources is largely unknown.
The tet(X4)-carrying isolates were collected from human and livestock in several multiple regions of China. The whole genomic sequences of these isolates were either obtained from NCBI GenBank or determined by Illumina Hiseq 2500 and the MinION platform. The intact transposon region, ISCR2-tet(X4)-ISCR2, observed in a small number of isolates as the reference sequence to construct the transposon phylogeny. The diversity of the genetic environments of all ISCR2-tet(X4) elements were analyzed.
A 2760-bp element encompassing the tet(X4)-hydrolase-encoding gene, catD, located between two ISCR2 elements was highly conserved in all isolates and could form an RC transposable unit (RC-TU). ISCR2 could also capture more resistance genes and formed a larger RC-TU base on RC transposition. However, the ISCR2-mediated RC-TUs were constantly truncated and inserted by other IS elements, indicating frequent recombination events. Of these elements, IS26 disrupted both the upstream and downstream ISCR2-mediated RC-TUs, indicating that IS26 captured tet(X4), thus leading to a wider spread of tet(X4).
These results confirmed the critical role of ISCR2 for dissemination and co-transmission of tet(X4) and other resistance genes. More effort is needed to monitor the variation tendencies of tet(X4)-carrying mobile elements and determine the driving factors for disseminating transferable tigecycline resistance.
移动替加环素耐药基因 tet(X) 变体已从动物、人类及其相关环境中出现，成为多种病原体，这可能对公共健康构成威胁。插入序列 ISCR2 通过滚环（RC）转位携带 tet(X4) 进行水平转移。然而，不同来源的 ISCR2 和 tet(X4) 的多样性在很大程度上尚不清楚。
从中国多个地区的人和牲畜中收集携带 tet(X4)的分离株。这些分离株的全基因组序列要么从 NCBI GenBank 获得，要么通过 Illumina Hiseq 2500 和 MinION 平台确定。在少数分离株中观察到的完整转座子区域 ISCR2-tet(X4)-ISCR2 作为参考序列构建转座子系统发育。分析了所有 ISCR2-tet(X4) 元件的遗传环境多样性。
一个包含 tet(X4) 水解酶编码基因 catD 的 2760-bp 元件位于两个 ISCR2 元件之间，在所有分离株中高度保守，可形成 RC 可移动单元（RC-TU）。ISCR2 还可以捕获更多的耐药基因，并基于 RC 转位形成更大的 RC-TU。然而，ISCR2 介导的 RC-TUs 不断被其他 IS 元件截断和插入，表明频繁发生重组事件。在这些元件中，IS26 破坏了上下游 ISCR2 介导的 RC-TUs，表明 IS26 捕获了 tet(X4)，从而导致 tet(X4) 的广泛传播。
这些结果证实了 ISCR2 在传播和共同转移 tet(X4) 和其他耐药基因方面的关键作用。需要进一步努力监测携带 tet(X4)的可移动元件的变异趋势，并确定传播可转移替加环素耐药性的驱动因素。
