Zhao Wei-Hua, Hu Zhi-Qing, Chen Gelin, Ito Ribu, Shimamura Tadakatsu
Department of Microbiology and Immunology, Showa University Hospital, Showa University School of Medicine, Tokyo, Japan.
Chemotherapy. 2008;54(1):31-7. doi: 10.1159/000112315. Epub 2007 Dec 7.
Some clinical isolates of Serratia marcescens showed high-level resistance to expanded-spectrum cephalosporins alone and in combination with beta-lactamase inhibitor, but the beta-lactamase extracted from these strains was sensitive to the inhibitors. This study examines the possible mechanisms responsible for the discrepancy.
Three clinical isolates of S. marcescens bore the bla(TEM) gene coded on a plasmid. This was confirmed by detection of the bla gene using PCR analysis and by transferring resistance determinants to Escherichia coli via conjugation and transformation. All of the E. coli transconjugants and transformants acquired a similar level of resistance to penicillins and narrow-spectrum cephalosporins, and showed the reduced susceptibility to expanded-spectrum cephalosporins alone and in combination with clavulanate. As a result of the highly constitutive expression of the TEM gene, up to 247-690 U of beta-lactamase were produced by 10(10) cells of wild-type S. marcescens and the transconjugants and transformants. In the presence of 0.24 U/ml of TEM enzyme, the minimum inhibition concentrations of cefotaxime against E. coli ATCC 25922 increased from 0.125 to 512 microg/ml. The TEM-type beta-lactamase extracted from these strains was sensitive to clavulanate, and 62.2-92.1% of its activity was inhibited after preincubation with 0.1 mM clavulanate.
The TEM-type beta-lactamase plays a critical role in the resistance of S. marcescens to beta-lactams, and the hyperproduction of inhibitor-susceptible TEM beta-lactamase is responsible for the resistance to beta-lactam-beta-lactamase inhibitor combinations.
一些粘质沙雷氏菌临床分离株对广谱头孢菌素单独使用以及与β-内酰胺酶抑制剂联合使用均表现出高水平耐药，但从这些菌株中提取的β-内酰胺酶对抑制剂敏感。本研究探讨了造成这种差异的可能机制。
三株粘质沙雷氏菌临床分离株携带位于质粒上的bla(TEM)基因。通过PCR分析检测bla基因以及通过接合和转化将耐药决定簇转移至大肠杆菌，证实了这一点。所有大肠杆菌转接合子和转化子对青霉素和窄谱头孢菌素获得了相似水平的耐药性，并且对单独使用的广谱头孢菌素以及与克拉维酸联合使用时均表现出敏感性降低。由于TEM基因的高度组成型表达，野生型粘质沙雷氏菌以及转接合子和转化子的10(10)个细胞可产生高达247 - 690 U的β-内酰胺酶。在存在0.24 U/ml TEM酶的情况下，头孢噻肟对大肠杆菌ATCC 25922的最低抑菌浓度从0.125 μg/ml增加至512 μg/ml。从这些菌株中提取的TEM型β-内酰胺酶对克拉维酸敏感，在与0.1 mM克拉维酸预孵育后，其活性的62.2 - 92.1%被抑制。
TEM型β-内酰胺酶在粘质沙雷氏菌对β-内酰胺类药物的耐药性中起关键作用，对抑制剂敏感的TEMβ-内酰胺酶的过量产生是对β-内酰胺-β-内酰胺酶抑制剂联合用药耐药的原因。
