In this study, we investigated the colistin heteroresistance patterns in Acinetobacter baumannii isolates. To identify colistin heteroresistance, population analysis profiling was performed for six in vitro colistin-susceptible A. baumannii isolates. Survival rates with and without prior exposure to colistin (at concentrations between 0 and 32 mg/L) were measured in media with and without colistin. Amino acid substitutions were also detected in colonies that survived in media with 4 mg/L colistin without further antibiotic treatment in six A. baumannii isolates. A stability test was also performed to investigate whether colistin resistance is maintained without antibiotic treatment. Although only three isolates showed typical colistin heteroresistance pattern, colistin-resistant populations were identified even without prior exposure to colistin in all A. baumannii isolates. Nearly all colonies of typical colistin-heteroresistant isolates (Type I heteroresistance) that survived after exposure to high colistin concentrations were found to be colistin-resistant, whereas no resistant colonies were identified in the other isolates (Type II heteroresistance). Stability tests showed that most of the surviving populations in media with 4 mg/L colistin without further antibiotic exposure failed to preserve resistance to colistin. Colistin-resistant populations also showed either no change in amino acid sequences, or diverse amino acid substitutions. We identified two types of colistin heteroresistance in A. baumannii isolates. Because Type I colistin-heteroresistant A. baumannii isolates could not be eradicated in vitro by high concentrations of colistin, differentiating two colistin heteroresistance types would be important for the treatment of A. baumannii infections using colistin.

在这项研究中，我们调查了鲍曼不动杆菌分离株中的大肠菌素异抗性模式。为了鉴定大肠菌素的异抗性，对六种体外大肠菌素敏感的鲍曼不动杆菌进行了种群分析。在有和没有粘菌素的培养基中测定有无粘菌素暴露的生存率（浓度在0和32 mg / L之间）。在6例鲍曼不动杆菌中，在没有进一步抗生素处理的情况下，在没有4mg / L大肠菌素的培养基中存活的菌落中也检测到氨基酸取代隔离株。还进行了稳定性测试，以研究未经抗生素治疗是否能保持大肠粘菌素抗性。尽管只有三个分离株显示出典型的大肠菌素异抗性模式，但即使在所有鲍曼不动杆菌中都未暴露于大肠菌素的情况下，仍能鉴定出大肠菌素抗性种群。隔离株。发现在暴露于高粘菌素浓度后存活的典型大肠粘菌素-异抗性分离株（I型异种抗性）几乎所有菌落均对粘菌素具有抗性，而在其他分离株中未鉴定出抗性菌落（II型异种抗性）。稳定性测试表明，在没有进一步暴露于抗生素的情况下，含有4 mg / L大肠菌素的培养基中大多数幸存的种群无法保持对大肠菌素的抗性。抗共利斯汀的种群也没有显示氨基酸序列的变化或多种氨基酸取代。我们在鲍曼不动杆菌菌株中鉴定出两种类型的粘菌素异抗性。因为无法在体外根除I型大肠菌素异抗性鲍曼不动杆菌通过高浓度的粘菌素，区分两种粘菌素异抗性类型对于使用粘菌素治疗鲍曼不动杆菌感染很重要。