Genetic relatedness of serial rectal isolates of <i>Acinetobacter baumannii</i> in an adult intensive care unit of a tertiary hospital in Kuwait

Acinetobacter baumannii is an opportunistic pathogen of intensive care unit (ICU) patients. A. baumannii colonizes many parts of the body including the gastrointestinal tract. Endemic and epidemic strains are polyclonal. There is no clarity on the origin of polyclonality of A. baumannii. The objective of the study was to define the genetic relatedness of serial isolates and the origin of polyclonality. Serial rectal isolates from ICU patients whose rectum was colonized on ≥5 sampling occasions were selected. From a total of 32 eligible colonized patients, isolates from a subgroup of 13 patients (a total of 108 isolates) showing different patterns of colonization as revealed by pulsed-field gel electrophoresis (PFGE) were studied. The isolates were analyzed by PFGE pulsotypes, sequence types (STs) by multi-locus sequence typing (MLST) and clonal complex (CC) by eBURST analysis. Serial isolates constituted a mixture of identical, related and unrelated pulsotypes. Analysis by STs and CCs were less discriminatory. The data suggest a combination of an initial colonizing isolate undergoing mutation as well as colonization by independent isolates. Further clarity on the origin of diversity should be better obtained by whole-genome sequencing.鲍曼不动杆菌（Acinetobacter baumannii）是一种可感染重症监护病房（intensive care unit, ICU）患者的机会致病菌。该菌可定植于人体多个部位，其中包括胃肠道。地方性流行与暴发流行菌株均呈多克隆性，目前学界对鲍曼不动杆菌多克隆性的起源尚不清楚。本研究旨在明确系列分离株的遗传相关性，以及该菌多克隆性的起源。本研究选取了重症监护病房中经≥5次采样均检出直肠定植的患者的系列直肠分离株。在共计32例符合入组标准的定植患者中，针对其中13例患者的分离株展开研究，共计获得108株分离株；经脉冲场凝胶电泳（pulsed-field gel electrophoresis, PFGE）检测，这些患者的定植模式存在差异。研究人员通过PFGE脉冲型对分离株进行分型，借助多位点序列分型（multi-locus sequence typing, MLST）确定序列型（sequence types, STs），并通过eBURST分析推导克隆复合体（clonal complex, CC）。系列分离株包含完全一致、亲缘相关以及无关联的脉冲型。序列型与克隆复合体分型的分辨能力相对较弱。研究数据表明，初始定植分离株发生突变与独立定植菌株侵入这两种机制共同存在。未来可通过全基因组测序进一步明确该菌多样性的起源。