Dejun Liu1, Tao Wang2, Dongyan Shao1, Huangwei Song1, Weishuai Zhai1, Chengtao Sun1, Ying Zhang3, Muchen Zhang1, Yulin Fu1, Rong Zhang4, Tao He5, Ziquan Lv6, Li Bai7, Congming Wu1, Yuebin Ke6, Yang Wang1, Zhangqi Shen8. 1. College of Veterinary Medicine, China Agricultural University, Beijing 100193, China. 2. Department of Gastroenterology, the fourth Medical Center of PLA General Hospital, 100048, China. 3. Department of Microbiology, The General Hospital of PLA, Beijing 100853, China. 4. The Second Affiliated Hospital of Zhejiang University, Zhejiang University, Hangzhou, Zhejiang 310009, China. 5. Jiangsu Key Laboratory for Food Quality and Safety-State Key Laboratory Cultivation Base of Ministry of Science and Technology, Institute of Food Safety and Nutrition, Jiangsu Academy of Agricultural Sciences, Nanjing, Jiangsu 210014, China. 6. Key Laboratory of Genetics & Molecular, Medicine of Shenzhen, Shenzhen Center for Disease Control and Prevention, Shenzhen 518000, China. 7. Key Laboratory of Food Safety Risk Assessment, National Health Commission of the People's Republic of China, China National Center for Food Safety Risk Assessment, Beijing 100022, China. 8. College of Veterinary Medicine, China Agricultural University, Beijing 100193, China. Electronic address: szq@cau.edu.cn.
Abstract
BACKGROUND: 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. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.
BACKGROUND: 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. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.