Yi Mei-ying, Wang Peng-yuan, Huang Han-ju, Liu Yu-cun
Department of Microbiology, School of Basic Medical Sciences, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China.
Zhonghua Yi Xue Za Zhi. 2006 Feb 21;86(7):457-62.
To investigate the mechanisms of carbapenem resistance in Pseudomonas aeruginosa (PA).
Forty-nine strains of PA were isolated from surgical intensive care unit during a period of 3 years. The levels of outer membrane protein OprD and OprN were measured by Western blotting. RT-PCR was used to measure the transcription levels of mexA gene. The metallo-beta-lactamase genes IMP and VIM and the negative regulator gene mexR for mexAB-OprM operon were amplified. The DNA fragments were sequenced by automated ABI PRISM 3700 sequencer.
42 of the 49 strains were resistant to carbapenem. 23 of the 42 strains showed loss of OprD and were all resistant to imipenem, but only one strain was resistant to meropenem. 18 of the 42 strains had a decreased OprD expression, 17 of which were resistant to Imipenem, and 3 were resistant to meropenem as well. 7 strains expressed OprD, all of which were sensitive to carbapenem. 27 strains overexpressed the mexAB-OprM. The resistant rate to imipenem of the mexAB-OprM overexpression group was 86.4%, not significantly different from that of the mexAB-OprM low expression group (81.5%, chi(2) = 0.005, P = 0.943). But the resistant rate to meropenem of the mexAB-OprM overexpression group was 44.4%, statistically higher than that of mexAB-OprM low expression group (13.6%, chi(2) = 5.417, P = 0.020). Nucleotide sequences and deduced amino acid sequences analysis revealed that eight strains overexpressed mexAB-OprM carried mutations in mexR gene, 7 of which had amino acid substitutions in MexR protein, and one of which had terminal code at the position of amino acid 32. 14 strains were found expressing OprN. Neither IMP gene nor VIM gene was found in the isolates.
In the clinical strains from SICU, the imipenem resistance is mainly mediated by OprD deficiency or loss. Overexpression of MexAB-OprM is the primary mechanism of meropenem resistance, which is upregulated by mutations in mexR gene. Metallo-beta-lactamases IMP and VIM are rarely seen.
探讨铜绿假单胞菌（PA）对碳青霉烯类耐药的机制。
在3年期间从外科重症监护病房分离出49株PA。通过蛋白质免疫印迹法检测外膜蛋白OprD和OprN的水平。采用逆转录聚合酶链反应（RT-PCR）检测mexA基因的转录水平。扩增金属β-内酰胺酶基因IMP和VIM以及mexAB-OprM操纵子的负调控基因mexR。DNA片段通过自动ABI PRISM 3700测序仪进行测序。
49株菌株中有42株对碳青霉烯类耐药。42株中的23株显示OprD缺失，且均对亚胺培南耐药，但仅1株对美罗培南耐药。42株中的18株OprD表达降低，其中17株对亚胺培南耐药，3株也对美罗培南耐药。7株表达OprD，均对碳青霉烯类敏感。27株mexAB-OprM过表达。mexAB-OprM过表达组对亚胺培南的耐药率为86.4%，与mexAB-OprM低表达组（81.5%）无显著差异（χ² = 0.005，P = 0.943）。但mexAB-OprM过表达组对美罗培南的耐药率为44.4%，统计学上高于mexAB-OprM低表达组（13.6%）（χ² = 5.417，P = 0.020）。核苷酸序列和推导的氨基酸序列分析显示，8株mexAB-OprM过表达的菌株mexR基因发生突变，其中7株MexR蛋白有氨基酸替换，1株在氨基酸32位有终止密码。发现14株表达OprN。分离株中未发现IMP基因和VIM基因。
在外科重症监护病房的临床菌株中，亚胺培南耐药主要由OprD缺陷或缺失介导。MexAB-OprM过表达是美罗培南耐药的主要机制，其由mexR基因的突变上调。金属β-内酰胺酶IMP和VIM很少见。
