Department of Clinical Laboratory, Renji Hospital, School of Medicine, Shanghai, China.
Chemotherapy. 2011;57(1):77-84. doi: 10.1159/000323620. Epub 2011 Feb 23.
To investigate the role of outer membrane proteins in Acinetobacter baumannii resistant to imipenem, 2 strains were procured from the same patient.
The imipenem-resistant strain was obtained following a period of imipenem treatment in vivo. The multilocus sequence typing and repetitive extragenic palindromic PCR results indicated that the imipenem-resistant strain originated from the sensitive one.
Isoelectric focusing detected no carbapenemases, with neither OXA carbapenemases nor metallo-β-lactamases found. Mass spectrophotometric analysis revealed that 3 outer membrane proteins were expressed differentially in the 2 strains: 2 downregulated proteins (OprD and CarO) and 1 upregulated the 34-kDa efflux pump protein in the resistant strain. A 32-fold decrease in the MIC for imipenem in the presence of Phe-Arg-β-naphthylamide in the same strain indicated a possible involvement of the efflux pump mechanism in its resistance, which was consistent with the findings that the mRNA expression of the 34-kDa efflux pump gene was almost fivefold upregulated in the imipenem-resistant strain compared with that in the imipenem-sensitive strain. Such a significant difference, however, was not found in the expression of AdeB and AdeJ between the 2 strains, and AdeE was not detected.
Our results suggested that downregulation of outer membrane proteins in conjunction with efflux pump overexpression might contribute to imipenem resistance induced in vivo in A. baumannii.
为了研究外膜蛋白在耐亚胺培南鲍曼不动杆菌中的作用，从同一患者中分离出 2 株菌。
耐亚胺培南菌株是在体内亚胺培南治疗后获得的。多位点序列分型和重复基因外回文 PCR 结果表明，耐亚胺培南菌株来源于敏感菌株。
等电聚焦未检测到碳青霉烯酶，既没有 OXA 碳青霉烯酶，也没有金属β-内酰胺酶。质谱分析显示，2 株菌中有 3 种外膜蛋白表达存在差异：2 种下调蛋白（OprD 和 CarO）和 1 种上调 34 kDa 外排泵蛋白在耐药株中表达。在同一菌株中加入苯丙氨酸-精氨酸-β-萘基酰胺后，亚胺培南的 MIC 值降低了 32 倍，这表明外排泵机制可能参与了其耐药性，这与 34 kDa 外排泵基因的 mRNA 表达在耐亚胺培南菌株中几乎上调了 5 倍的结果一致，而在 2 株菌之间未发现 AdeB 和 AdeJ 的表达有显著差异，也未检测到 AdeE。
我们的结果表明，外膜蛋白下调与外排泵过度表达可能导致鲍曼不动杆菌体内诱导的亚胺培南耐药。
