Yu Yang, Cui Chao-Yue, Kuang Xu, Chen Chong, Wang Min-Ge, Liao Xiao-Ping, Sun Jian, Liu Ya-Hong
Guangdong Provincial Key Laboratory of Veterinary Pharmaceutics Development and Safety Evaluation, South China Agricultural University, Guangzhou, China.
National Risk Assessment Laboratory for Antimicrobial Resistance of Animal Original Bacteria, South China Agricultural University, Guangzhou, China.
Front Microbiol. 2021 Aug 23;12:716393. doi: 10.3389/fmicb.2021.716393. eCollection 2021.
Carbapenems, colistin, and tigecycline are critically important antibiotics in clinics. After the global appearance of and mediating the resistance to carbapenems and colistin, respectively, tigecycline becomes the last-resort drug against severe human infections caused by multidrug-resistant bacteria. Recently, a mobile tigecycline resistance gene (X4) has been identified in , , and that causes high resistance to tigecycline and other tetracyclines. In this study, the prevalence of (X4) in isolates from duck and goose farms in Southeast China was identified and characterized.
Feces, soil, sewage, and dust samples were collected from duck and goose farms along with the southeast coast provinces of China. Antimicrobial susceptibility testing and polymerase chain reaction screening were performed to investigate the phenotype and genotype of tigecycline resistance. Conjugation, S1 pulsed-field gel electrophoresis (PFGE), and whole-genome sequencing were used to determine the transferability, genetic location, and the genomic characteristics of (X4).
In total, 1,716 samples were collected, and 16 isolates (0.9%) recovered from Guangdong, Shandong, and Jiangsu were positive for (X4) gene with tigecycline minimum inhibitory concentrations ≥16 mg/L. Notably, among these (X4)-positive isolates, seven of them were from the environment samples (soil and sewage). PFGE and multilocus sequence typing demonstrated that ST3997 was the most prevalent sequence type (eight isolates, 50%) in Jiangsu province. By conjugation assays, 11 isolates were able to transfer (X4) plasmid to C600 recipient, and these plasmids belonged to IncHI1 and IncX1 detected by sequence analysis. (X4) was found adjacent to an insertion sequence IS downstream and a D gene upstream for all isolates. In addition, multiple-drug resistance to tigecycline, chlortetracycline, ampicillin, florfenicol, ciprofloxacin, gentamicin, trimethoprim/sulfamethoxazole, and fosfomycin was profiled in most of the (X4)-positive isolates.
The identification of (X4) harboring strains in duck farms and their surrounding environment enlarges our knowledge of the variety and prevalence of tigecycline resistance. The prevalence of (X4) raises concern for the use of tetracyclines in animal farming, and the (X4) gene should be listed as primary gene for resistance surveillance.
碳青霉烯类、黏菌素和替加环素是临床中至关重要的抗生素。在分别介导对碳青霉烯类和黏菌素耐药性的全球出现后，替加环素成为对抗由多重耐药菌引起的严重人类感染的最后手段药物。最近，在、和中鉴定出一种可移动的替加环素耐药基因（X4），该基因对替加环素和其他四环素类药物具有高度耐药性。在本研究中，对中国东南部鸭场和鹅场分离株中（X4）的流行情况进行了鉴定和特征分析。
从中国东南沿海省份的鸭场和鹅场采集粪便、土壤、污水和灰尘样本。进行药敏试验和聚合酶链反应筛选以研究替加环素耐药性的表型和基因型。采用接合试验、S1脉冲场凝胶电泳（PFGE）和全基因组测序来确定（X4）的可转移性、基因定位和基因组特征。
共采集1716份样本，从广东、山东和江苏分离出16株（0.9%）对（X4）基因呈阳性且替加环素最低抑菌浓度≥16mg/L的菌株。值得注意的是，在这些（X4）阳性菌株中，有7株来自环境样本（土壤和污水）。PFGE和多位点序列分型表明，ST3997是江苏省最常见的序列类型（8株，50%）。通过接合试验，11株菌株能够将（X4）质粒转移至受体菌C600，经序列分析检测这些质粒属于IncHI1和IncX1。在所有分离株中，发现（X4）位于下游的插入序列IS和上游的D基因附近。此外，大多数（X4）阳性分离株对替加环素、金霉素、氨苄西林、氟苯尼考、环丙沙星、庆大霉素、甲氧苄啶/磺胺甲恶唑和磷霉素呈现多重耐药。
在鸭场及其周边环境中鉴定出携带（X4）的菌株，扩大了我们对替加环素耐药性种类和流行情况的认识。（X4）的流行引发了对四环素类药物在动物养殖中使用情况的关注，（X4）基因应列为耐药监测的主要基因。
