McGettigan Shannon E, Hu Baofeng, Andreacchio Kathleen, Nachamkin Irving, Edelstein Paul H
Department of Pathology and Laboratory Medicine, Hospital of the University of Pennsylvania, 3400 Spruce St., Philadelphia, PA 19104-4283, USA.
J Clin Microbiol. 2009 Sep;47(9):2970-4. doi: 10.1128/JCM.00319-09. Epub 2009 Jul 8.
CTX-M beta-lactamases were thought to be rare in the United States, but a recent study in Texas showed that up to 70% of extended-spectrum beta-lactamase (ESBL)-containing members of the Enterobacteriaceae family were CTX-M positive (J. S. Lewis, M. Herrera, B. Wickes, J. E. Patterson, and J. H. Jorgensen, Antimicrob. Agents Chemother. 51:4015-4021, 2007). We used PCR to detect CTX-M in all 291 extended-spectrum cephalosporin-resistant gram-negative bacteria isolated in our laboratory during 2007. Thirty (48%) Escherichia coli isolates, 6 (3%) Klebsiella sp. isolates, and 7 (100%) Proteus mirabilis isolates tested were CTX-M positive, with 15% of all Enterobacteriaceae tested being positive. The E. coli CTX-M groups were I (57%), IV (37%), II (3%), and not groupable (3%); three of the group IV isolates were positive for CTX-M-18, and three of the group I isolates were positive for CTX-M-15. One of seven positive P. mirabilis isolates was in group II, with the remainder being positive for a CTX-M-25-like beta-lactamase; and 33% of the Klebsiella sp. isolates were in group I or IV, with the remainder not being in groups I to IV. CTX-M-producing bacteria were isolated from urine (n = 13), blood (n = 13), wounds (n = 12), and the respiratory tract (n = 4). All 31 CTX-M-positive isolates tested for the presence of ESBL were confirmed to produce ESBLs by the use of tests recommended by the CLSI. Pulsed-field gel electrophoresis of the CTX-M-positive isolates showed that six P. mirabilis isolates were clonal and that there were seven different E. coli clusters. Five of seven P. mirabilis isolates were from blood cultures. The CLSI tests for the confirmation of ESBL production reliably detect these isolates if both cefotaxime and ceftazidime are tested, but only about half would be classified as a possible CTX-M producers on the basis of the antibiogram alone. A new panprimer set increases the ability to detect CTX-M-producing strains. CTX-M-positive bacteria are common in our geographic region, are often invasive, and, with the exception of P. mirabilis, are multiclonal.
CTX-Mβ-内酰胺酶在美国曾被认为较为罕见，但德克萨斯州最近的一项研究表明，肠杆菌科中含有超广谱β-内酰胺酶（ESBL）的菌株中，高达70%的菌株CTX-M呈阳性（J.S.刘易斯、M.埃雷拉、B.威克斯、J.E.帕特森和J.H.乔根森，《抗菌药物与化疗》51:4015 - 4021，2007年）。我们运用聚合酶链反应（PCR）检测了2007年在我们实验室分离出的所有291株对超广谱头孢菌素耐药的革兰氏阴性菌中的CTX-M。检测的30株（48%）大肠杆菌分离株、6株（3%）克雷伯菌属分离株和7株（100%）奇异变形杆菌分离株CTX-M呈阳性，所有检测的肠杆菌科菌株中有15%呈阳性。大肠杆菌的CTX-M组为I组（57%）、IV组（37%）、II组（3%）以及无法分组（3%）；IV组的3株分离株CTX-M - 18呈阳性，I组的3株分离株CTX-M - 15呈阳性。7株阳性奇异变形杆菌分离株中有1株属于II组，其余对一种类似CTX-M - 25的β-内酰胺酶呈阳性；33%的克雷伯菌属分离株属于I组或IV组，其余不属于I至IV组。产CTX-M的细菌分离自尿液（n = 13）、血液（n = 13）、伤口（n = 12）和呼吸道（n = 4）。对所有31株CTX-M阳性分离株进行ESBL检测，按照临床和实验室标准协会（CLSI）推荐的试验，证实均产ESBL。对CTX-M阳性分离株进行脉冲场凝胶电泳显示，6株奇异变形杆菌分离株为克隆株，大肠杆菌有7个不同的聚类。7株奇异变形杆菌分离株中有5株来自血培养。如果同时检测头孢噻肟和头孢他啶，CLSI用于确认ESBL产生的试验能够可靠地检测出这些分离株，但仅根据抗菌谱，只有约一半可能被归类为CTX-M产菌。一套新的通用引物提高了检测产CTX-M菌株的能力。产CTX-M的细菌在我们所在地区很常见，常具有侵袭性，除奇异变形杆菌外，多为多克隆菌。
