Colistin is the last resort for the treatment of infections with carbapenem-resistant (CR) Gram-negative bacteria particularly Acinetobacter baumannii (CRAB). Currently, both colistin-resistant and -heteroresistant A. baumannii isolates have been reported globally. We therefore investigated the colistin heteroresistance rate in 75 non-duplicate colistin-susceptible CRAB clinical isolates from a Thai university collected in 2016. Minimum inhibitory concentrations (MICs) of colistin for all isolates were determined by broth microdilution method and carbapenemase genes were detected by PCR methods. All isolates were genotyped by ERIC-PCR method and screened for colistin heteroresistance by modified population analysis profile (PAP) method. The colistin MIC range for the 75 isolates was 0.5–2 µg/mL, with MIC50 and MIC90 of 1 and 2 µg/mL, respectively. Thirty-three isolates (44%) were considered colistin-heteroresistant with subpopulations growing at 3–8 μg/mL of colistin. After three daily passages of the subpopulations on antibiotic-free medium, their colistin MICs ranged from 4 to > 32 µg/mL, with MIC50 and MIC90 of 32 and > 32 µg/mL, respectively. Eight different ERIC-PCR profiles were obtained among the 33 isolates and all carried blaOXA-23-like. The high rate of colistin heteroresistance in the CRAB isolates highlights the possibility of treatment failure of CRAB infections by colistin due to the selection of colistin-resistant subpopulations.

中文翻译：

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来自泰国大学医院的耐碳青霉烯类鲍曼不动杆菌临床分离株的粘菌素异抗性

粘菌素是治疗耐碳青霉烯类 (CR) 革兰氏阴性菌尤其是鲍曼不动杆菌 (CRAB) 感染的最后手段。目前，全球已报道了多粘菌素耐药和异种耐药鲍曼不动杆菌分离株。因此，我们研究了 2016 年从泰国大学收集的 75 个非重复的多粘菌素敏感 CRAB 临床分离株的多粘菌素异抗率。所有分离株的粘菌素最低抑制浓度 (MIC) 采用肉汤微量稀释法测定，碳青霉烯酶基因通过 PCR 检测方法。所有分离株均通过 ERIC-PCR 方法进行基因分型，并通过改良种群分析谱 (PAP) 方法筛选粘菌素异源抗性。75 个分离株的粘菌素 MIC 范围为 0.5–2 µg/mL，MIC50 和 MIC90 分别为 1 和 2 µg/mL。33 个分离株 (44%) 被认为对多粘菌素具有异质性，其中亚群以 3-8 μg/mL 的多粘菌素生长。亚群在无抗生素培养基上每天传代 3 次后，其粘菌素 MIC 范围为 4 至 > 32 µg/mL，MIC50 和 MIC90 分别为 32 和 > 32 µg/mL。在 33 个分离株中获得了 8 个不同的 ERIC-PCR 谱，并且都携带 blaOXA-23 样。CRAB 分离株中多粘菌素异抗性的高发生率凸显了由于选择多粘菌素耐药亚群，多粘菌素治疗 CRAB 感染失败的可能性。32 µg/mL，MIC50 和 MIC90 分别为 32 和 > 32 µg/mL。在 33 个分离株中获得了 8 个不同的 ERIC-PCR 谱，并且都携带 blaOXA-23 样。CRAB 分离株中多粘菌素异抗性的高发生率凸显了由于选择多粘菌素耐药亚群，多粘菌素治疗 CRAB 感染失败的可能性。32 µg/mL，MIC50 和 MIC90 分别为 32 和 > 32 µg/mL。在 33 个分离株中获得了 8 个不同的 ERIC-PCR 谱，并且都携带 blaOXA-23 样。CRAB 分离株中多粘菌素异抗性的高发生率凸显了由于选择多粘菌素耐药亚群，多粘菌素治疗 CRAB 感染失败的可能性。