Barin Juliana, Martins Andreza Francisco, Heineck Bianca Lucia, Barth Afonso Luis, Zavascki Alexandre Prehn
Ann Clin Microbiol Antimicrob. 2013 Jul 2;12:15. doi: 10.1186/1476-0711-12-15.
Resistance rates to polymyxin B in surveillance studies have been very low despite its increasing use worldwide as the last resort therapy for multidrug-resistant Gram-negative bacilli. However, two other resistance phenotypes, hetero- and adaptive resistance, have been reported to polymyxin. We aimed to investigate the presence of polymyxin B hetero- and adaptive resistance and evaluate its stability in carbapenem-resistant Acinetobacter baumannii (CRAB) clinical isolates.
CRAB isolates were recovered from hospitalized patients at three Brazilian hospitals. Hetero-resistance was determined by population analysis profile (PAP). Adaptive resistance was evaluated after serial daily passages of isolates in Luria-Bertani broth containing increasing polymyxin B concentrations. MICs of polymyxin B of colonies growing at the highest polymyxin B concentration were further determined after daily sub-cultured in antibiotic-free medium and after storage at -80°C, in some selected isolates.
Eighty OXA-23-producing CRAB isolates were typed resulting in 15 distinct clones. Twenty-nine randomly selected isolates (at least one from each clone) were selected for hetero- resistance evaluation: 26 (90%) presented growth of subpopulations with higher polymyxin B MIC than the original one in PAP. No isolate has grown at polymyxin B concentrations higher than 2 mg/L. Polymyxin B MICs of subpopulations remained higher than the original population after daily passages on antibiotic-free medium but returned to the same or similar levels after storage. Twenty-two of the 29 isolates (at least one from each clone) were evaluated for adaptive resistance: 12 (55%) presented growth in plates containing 64 mg/L of polymyxin B. Polymyxin B MICs decreased after daily passages on antibiotic-free medium and returned to the same levels after storage.
The presence of subpopulations with higher polymyxin B MIC was extremely common and high-level adaptive resistance was very frequent in CRAB isolates.
尽管多粘菌素B在全球范围内作为耐多药革兰氏阴性杆菌的最后一线治疗药物使用日益增加，但监测研究中的耐药率一直很低。然而，多粘菌素还存在另外两种耐药表型，即异质性耐药和适应性耐药。我们旨在调查耐碳青霉烯鲍曼不动杆菌（CRAB）临床分离株中多粘菌素B异质性耐药和适应性耐药的存在情况，并评估其稳定性。
从巴西三家医院的住院患者中分离出CRAB菌株。通过群体分析谱（PAP）确定异质性耐药。在含有递增浓度多粘菌素B的Luria-Bertani肉汤中对菌株进行连续每日传代后，评估适应性耐药。在一些选定的分离株中，将在最高多粘菌素B浓度下生长的菌落的多粘菌素B最低抑菌浓度（MIC）在无抗生素培养基中每日传代培养后以及在-80°C保存后进一步测定。
对80株产OXA-23的CRAB菌株进行分型，得到15个不同的克隆。随机选择29株分离株（每个克隆至少一株）进行异质性耐药评估：26株（90%）在PAP中呈现出多粘菌素B MIC高于原始菌株的亚群生长。没有分离株能在高于2mg/L的多粘菌素B浓度下生长。在无抗生素培养基中每日传代后，亚群的多粘菌素B MIC仍高于原始群体，但保存后恢复到相同或相似水平。对29株分离株中的22株（每个克隆至少一株）进行适应性耐药评估：12株（55%）在含有64mg/L多粘菌素B的平板上生长。在无抗生素培养基中每日传代后，多粘菌素B MIC降低，保存后恢复到相同水平。
多粘菌素B MIC较高的亚群在CRAB分离株中极为常见，高水平适应性耐药也很频繁。
