Shenzhen Institute of Respiratory Diseases, Second Clinical Medical College (Shenzhen People's Hospital), Jinan University; the First Affiliated Hospital (Shenzhen People's Hospital), Southern University of Science and Technology, Shenzhen, China.
Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China.
J Glob Antimicrob Resist. 2021 Jun;25:132-136. doi: 10.1016/j.jgar.2021.03.004. Epub 2021 Mar 21.
The aim of this study was to characterise a novel tet(X6)-carrying plasmid detected in a livestock-associated Acinetobacter towneri isolate.
PCR screening was performed to detect tet(X) variants in livestock-associated Acinetobacter spp. isolates. The tet(X6)-positive isolate was analysed by whole-genome sequencing. Functional cloning was performed to detect the activity of Tet(X6). Antibiotic susceptibility was determined by broth dilution and microbiological degradation assays. Site-directed mutagenesis was performed to identify the role of 23-Ala residue of Tet(X6) in tigecycline resistance.
The tet(X6) gene was detected on a 159-kb plasmid (pAT205) carried by a tigecycline-susceptible A. towneri isolate recovered from a swine faecal sample. The genetic context of tet(X6) [ΔISVsa3-tet(X6)-abh-guaA-ISVsa3] is highly similar to that of the reported plasmid-borne tet(X) variants, suggesting that it may represent a common structure mediating the dissemination of plasmid-borne tet(X) genes. Additional resistance genes detected on pAT205 were carried by a Tn6205-like region and a disrupted class 2 integron. Gene expression and microbiological degradation assays consistently suggested that the activity of tet(X6) is weaker than that of tet(X3) and tet(X4). The 23-Ala residue of the first FAD-binding site conferred higher activity to Tet(X6) than the Gly reside conserved in the other plasmid-borne tet(X) variants, indicating that the site might be under selection.
This study alerts to the silent dissemination possibility of tigecycline resistance mediated by a novel plasmid. Continuous monitoring of plasmid-borne tet(X) is imperative for tackling its dissemination.
本研究旨在对从动物源鲍曼不动杆菌分离株中检测到的新型 tet(X6) 携带质粒进行特征描述。
采用 PCR 筛选方法检测与动物源不动杆菌相关的 tet(X) 变体。对 tet(X6) 阳性分离株进行全基因组测序分析。采用功能克隆方法检测 Tet(X6) 的活性。通过肉汤稀释法和微生物降解试验测定抗生素敏感性。通过定点突变确定 Tet(X6) 中的 23-丙氨酸残基在替加环素耐药性中的作用。
从猪粪便样本中分离出的一株对替加环素敏感的鲍曼不动杆菌中，发现了 tet(X6) 基因位于一个 159kb 的质粒 (pAT205) 上。tet(X6) [ΔISVsa3-tet(X6)-abh-guaA-ISVsa3] 的基因结构与报道的质粒携带 tet(X) 变体非常相似，表明它可能代表了介导质粒携带 tet(X) 基因传播的常见结构。pAT205 上还检测到其他耐药基因，位于 Tn6205 样区域和一个破坏的 class 2 整合子上。基因表达和微生物降解试验一致表明，tet(X6) 的活性弱于 tet(X3) 和 tet(X4)。第一个 FAD 结合位点的 23-丙氨酸残基赋予 Tet(X6) 比其他质粒携带的 tet(X) 变体中保守的甘氨酸残基更高的活性，表明该位点可能受到选择。
本研究提醒人们注意新型质粒介导的替加环素耐药性的沉默传播可能性。持续监测质粒携带的 tet(X) 对于遏制其传播至关重要。
