Tofteland Ståle, Dahl Kristin H, Aasnæs Bettina, Sundsfjord Arnfinn, Naseer Umaer
Department of Clinical Microbiology, Sørlandet Hospital HF, Kristiansand, Norway.
Scand J Infect Dis. 2012 Dec;44(12):927-33. doi: 10.3109/00365548.2012.707330. Epub 2012 Sep 19.
Enterobacteriaceae exerting a high level of extended-spectrum cephalosporin (ESC) resistance have increased significantly in Norway in the last decade. Various mechanisms acting alone or in concert mediate variable levels of ESC resistance and pose great challenges in the implementation of screening strategies and treatment. This study was undertaken to document the prevalence of underlying mechanisms conferring resistance to ESCs in a nationwide collection of clinical isolates of Escherichia coli, Klebsiella pneumoniae, and Klebsiella oxytoca, before the increase in extended-spectrum β-lactamase (ESBL)-producing strains.
Consecutive E. coli (n = 2213), K. pneumoniae (n = 303), and K. oxytoca (n = 66) isolates from 23 Norwegian diagnostic laboratories were collected and examined for reduced susceptibility to ESCs. Isolates displaying minimum inhibitory concentrations (MICs) of > 2 mg/l by Etest to cefpodoxime and/or MICs > 1 mg/l to any other ESCs were included (n = 54; 35 E. coli, 11 K. pneumoniae, and 8 K. oxytoca). Isoelectric focusing for the detection of β-lactamases, and polymerase chain reactions (PCRs) with subsequent sequencing for detection of ESBLs CTX-M, TEM, and SHV, plasmid-mediated AmpC, OXA subtypes, and alterations of porin genes ompC and ompF, and quantitative reverse transcriptase (RT)-PCR for investigation of enhanced expression of chromosomal ampC were performed.
Eight E. coli isolates (0.4%) were ESBL producers and 20 (1.0%) were hyperproducers of the chromosomal ampC. Three K. pneumoniae isolates (1.1%) were ESBL producers, and all K. oxytoca isolates (n = 8; 13.6%) were OXY-hyperproducers. No definite mechanisms for reduced susceptibility to ESCs could be inferred for 7 E. coli (0.4%) and 8 K. pneumoniae (3.0%) isolates.
This study identified chromosomal AmpC-hyperproducing E. coli and OXY-hyperproducing K. oxytoca in addition to ESBLs in Enterobacteriaceae as major mechanisms of resistance to ESC, and documented their rates of prevalence for the first time in Norway.
在过去十年中，挪威产超广谱头孢菌素（ESC）高水平耐药的肠杆菌科细菌显著增加。多种单独或协同作用的机制介导了不同水平的ESC耐药性，给筛查策略的实施和治疗带来了巨大挑战。本研究旨在记录在产超广谱β-内酰胺酶（ESBL）菌株增加之前，挪威全国范围内收集的大肠埃希菌、肺炎克雷伯菌和产酸克雷伯菌临床分离株中赋予ESC耐药性的潜在机制的流行情况。
收集来自23家挪威诊断实验室的连续大肠埃希菌（n = 2213）、肺炎克雷伯菌（n = 303）和产酸克雷伯菌（n = 66）分离株，检测其对ESC的敏感性降低情况。纳入通过Etest法对头孢泊肟的最低抑菌浓度（MIC）> 2 mg/l和/或对任何其他ESC的MIC > 1 mg/l的分离株（n = 54；35株大肠埃希菌、11株肺炎克雷伯菌和8株产酸克雷伯菌）。进行等电聚焦检测β-内酰胺酶，以及聚合酶链反应（PCR）并随后测序检测ESBLs CTX-M、TEM和SHV、质粒介导的AmpC、OXA亚型，以及孔蛋白基因ompC和ompF的改变，并用定量逆转录（RT）-PCR研究染色体ampC的表达增强情况。
8株大肠埃希菌分离株（0.4%）产ESBL，20株（1.0%）为染色体ampC的高产株。3株肺炎克雷伯菌分离株（1.1%）产ESBL，所有产酸克雷伯菌分离株（n = 8；13.6%）为OXY高产株。7株大肠埃希菌（0.4%）和8株肺炎克雷伯菌（3.0%）分离株无法推断出对ESC敏感性降低的确切机制。
本研究确定除了肠杆菌科细菌中的ESBL外，染色体AmpC高产的大肠埃希菌和OXY高产的产酸克雷伯菌是对ESC耐药的主要机制，并首次在挪威记录了它们的流行率。
