Acinetobacter baumannii is involved in life-threatening nosocomial infections, mainly in the intensive care units (ICUs), and often colistin may represent the last therapeutic opportunity. The susceptibility to colistin of 51 epidemiologically typed A. baumannii strains isolated in 2017 from clinical samples of patients hospitalized in the ICU of a tertiary care academic hospital was investigated. All isolates were carbapenem-resistant due to the presence of the bla_OXA-23 gene in sequence group 1 (international clonal lineage II) and sequence group 4 (related to international clonal lineage II) isolates, and to the bla_OXA-24/40 gene in sequence group 2 (international clonal lineage I) isolates. Vitek^®2, agar diffusion, and broth microdilution tests showed major discordancy (≥2 dilution factors) in the minimum inhibitory concentration (MIC) values for colistin in 24 out of 51 isolates, resulting in erroneous reporting of qualitative susceptibility data for eight isolates. In growth kinetics experiments in the presence of colistin, five isolates grew with drug concentrations above the susceptibility breakpoint when incubated for >12 h, and three isolates showed the presence of heteroresistant subpopulations. This study highlights that the high frequency of isolation of carbapenem-resistant A. baumannii strains in high-risk infectious wards requires an accurate application of methods for detecting susceptibility to antibiotics, in particular to colistin, so as to ensure a correct therapeutic approach.

中文翻译：

---

Colistin对鲍曼不动杆菌的药敏试验：我们离真相还有多远？

鲍曼不动杆菌涉及威胁生命的医院感染，主要在重症监护病房（ICU）中发生，通常粘菌素可能代表了最后的治疗机会。调查了2017年从三级医疗学术医院ICU住院患者的临床样本中分离出的51种流行病学类型鲍曼不动杆菌对大肠菌素的敏感性。由于在序列组1（国际克隆谱系II）和序列组4（与国际克隆谱系II相关）分离物中以及bla _{OXA-24 / 40中}存在bla _OXA-23基因，因此所有分离株均对碳青霉烯耐药。序列组2（国际克隆谱系I）中的BacA基因分离。维特克^®如图2所示，琼脂扩散和肉汤微稀释测试显示51种分离物中的24种中大肠菌素的最低抑菌浓度（MIC）值存在重大不一致性（≥2个稀释因子），导致错误报告了8种分离物的定性敏感性数据。在粘菌素存在下的生长动力学实验中，当培养> 12 h时，有五种分离株生长，药物浓度高于敏感性断裂点，并且三株分离株显示存在异抗性亚群。这项研究强调，在高风险感染病房中对耐碳青霉烯类鲍曼不动杆菌的菌株的高频率分离需要准确应用检测抗生素（尤其是粘菌素）敏感性的方法，以确保正确的治疗方法。