Institute of Clinical Microbiology, Faculty of Medicine, Albert Szent-Györgyi Clinical Centre, University of Szeged, Szeged, Hungary.
J Antimicrob Chemother. 2011 Nov;66(11):2492-500. doi: 10.1093/jac/dkr339. Epub 2011 Aug 25.
The characterization of Bacteroides strains with regard to the cfxA gene, the MTn4555 mobilizable transposon, the role of penicillin-binding proteins (PBPs) and heterogeneous cefoxitin resistance.
Eighty-four randomly selected and 11 heterogeneously or highly cefoxitin-resistant Bacteroides isolates were included. Agar dilution and Etest methods were used for the determination of cefoxitin MICs. PCR experiments and nucleotide sequencing were used to detect the cfxA gene and the molecular features of MTn4555. Cefoxitin-binding experiments to determine its affinity (IC(50)) for PBPs and cefoxitinase assays were also applied. Southern blotting was used to determine the copy number of the cfxA genes.
Sixteen strains from the random collection proved to be positive for cfxA, and the MIC distribution for the cfxA-negative and -positive strains did not display a clear separation. The majority of the cfxA-positive strains in this collection harboured a 1.2 kb common region at the 3' end of MTn4555. This region encoded an open reading frame that exhibited homology to abortive phage infection proteins (AbiD). The cfxA genes were transferable only at low frequencies in conjugation experiments. In PBP affinity studies, the PBP-A and PBP3 species were largely insensitive to cefoxitin, whereas the other PBP species were affected at very low concentrations. Seven of the heterogeneously resistant strains were positive for cfxA and most of them had mutations in the regulatory regions of cfxA.
Major and minor roles for Bacteroides fragilis PBPs and the CfxA cefoxitinase, respectively, were inferred. The role of the newly recognized abiD may be to control the copy number of cfxA.
对 cfxA 基因、MTn4555 可移动转座子、青霉素结合蛋白（PBPs）和异质性头孢西丁耐药的拟杆菌菌株进行特征描述。
随机选取 84 株和 11 株异质性或高度头孢西丁耐药的拟杆菌分离株进行研究。琼脂稀释法和 Etest 法用于测定头孢西丁 MIC。PCR 实验和核苷酸测序用于检测 cfxA 基因和 MTn4555 的分子特征。还应用头孢西丁结合实验来确定其与 PBPs 的亲和力（IC50）和头孢西丁酶测定。Southern 印迹法用于确定 cfxA 基因的拷贝数。
随机采集的 16 株菌株被证明为 cfxA 阳性，cfxA 阴性和阳性菌株的 MIC 分布没有明显分离。该采集物中大多数 cfxA 阳性菌株在 MTn4555 的 3'末端具有 1.2kb 的共同区域。该区域编码一个开放阅读框，与流产噬菌体感染蛋白（AbiD）具有同源性。cfxA 基因在接合实验中仅以低频率可转移。在 PBP 亲和力研究中，PBP-A 和 PBP3 种属对头孢西丁基本不敏感，而其他 PBP 种属则在非常低的浓度下受到影响。7 株异质性耐药菌株为 cfxA 阳性，其中大多数在 cfxA 的调节区有突变。
推断出脆弱拟杆菌 PBPs 的主要和次要作用以及 CfxA 头孢西丁酶的作用。新发现的 abiD 的作用可能是控制 cfxA 的拷贝数。
