Department of Laboratory Medicine and Research Institute of Bacterial Resistance, Yonsei University College of Medicine, 120-752, 134 Shinchon-dong, Seodaemun-gu, Seoul, Republic of Korea.
Antimicrob Agents Chemother. 2010 Dec;54(12):5057-61. doi: 10.1128/AAC.00768-10. Epub 2010 Sep 27.
The aim of this study was to investigate the mechanisms involved in the meropenem resistance of Serratia marcescens clinical isolates. Meropenem-resistant (MIC range, 16 to 32 μg/ml) S. marcescens isolates were recovered from nine patients in a tertiary hospital in Seoul, South Korea, from June to November 2005. All the isolates shared identical or similar (>85% similarity) SpeI macrorestriction patterns, indicating clonal spread. PCR experiments did not detect any carbapenemase in those isolates. They carried the bla(CTX-M-22) gene located on a 150-kbp plasmid of the incompatibility group L/M; however, the addition of clavulanic acid exhibited few effects on meropenem MICs. Although meropenem MICs were reduced 4- to 16-fold with the addition of boronic acid, no plasmid-borne AmpC β-lactamase gene was detected in PCR experiments. Real-time quantitative PCR experiments showed that expression levels of the chromosomal ampC gene in those isolates were 87.06 to 155.76 times higher than that of the reference strain ATCC 8100. SDS-PAGE showed a lack of the 42-kDa outer membrane protein (OmpF). In combination with the overproduction of the chromosomal AmpC enzyme, the loss of OmpF may have played a role in the acquisition of meropenem resistance in our isolates.
本研究旨在探讨粘质沙雷氏菌临床分离株对美罗培南耐药的机制。2005 年 6 月至 11 月，从韩国首尔一家三级医院的 9 名患者中分离出耐美罗培南（MIC 范围为 16 至 32μg/ml）的粘质沙雷氏菌。所有分离株的 SpeI 宏观限制图谱相同或相似（>85%相似），表明存在克隆传播。PCR 实验未在这些分离株中检测到任何碳青霉烯酶。它们携带 bla(CTX-M-22)基因，位于不相容群 L/M 的 150kbp 质粒上；然而，添加克拉维酸对美罗培南 MIC 的影响很小。虽然添加硼酸可使美罗培南 MIC 降低 4 至 16 倍，但 PCR 实验未检测到质粒携带的 AmpC β-内酰胺酶基因。实时定量 PCR 实验显示，这些分离株的染色体 ampC 基因表达水平比参考菌株 ATCC 8100 高 87.06 至 155.76 倍。SDS-PAGE 显示缺乏 42kDa 外膜蛋白（OmpF）。与染色体 AmpC 酶的过度表达相结合，OmpF 的缺失可能在我们的分离株获得美罗培南耐药性中发挥了作用。
