Laboratoire MBA, Département de Biologie, Faculté de Sciences de Tunis, Campus Universitaire, 2092 Tunis, Tunisia.
Int J Food Microbiol. 2010 Feb 28;137(2-3):281-6. doi: 10.1016/j.ijfoodmicro.2009.12.003. Epub 2009 Dec 6.
The presence of broad-spectrum-cephalosporin-resistant Escherichia coli isolates and the implicated mechanisms of resistance were investigated in 79 food samples of animal origin obtained in different supermarkets and local butcheries in Tunisia. Ten of these samples (12.6%) harbored extended-spectrum beta-lactamase (ESBL) producing E. coli isolates and 13 ESBL-positive isolates were recovered (one or two/sample), which exhibited nine different Pulsed-Field-Gel-Electrophoresis (PFGE) patterns. ESBLs detected were the following: CTX-M-1 (10 strains), CTX-M-1+TEM-1b (2 strains) and CTX-M-1+TEM-20 (1 strain). The orf477 sequence was identified downstream of bla(CTX-M-1) gene in all 13 strains and ISEcp1 upstream in 9 strains. All ESBL-positive strains were included into phylogenetic group A or B1 (4 and 9 strains, respectively). Three of the 79 food samples (3.8%) contained broad-spectrum-cephalosporin-resistant and ESBL-negative E. coli isolates with AmpC phenotype. One isolate per sample was studied, and they showed unrelated PFGE patterns. The CMY-2 type beta-lactamase was identified in one of these 3 strains and specific point mutations in the promoter/attenuator region of ampC gene (at positions -42, -18, -1 and +58) were detected in the remaining two strains. Twelve ESBL-positive and one ESBL-negative E. coli strains contained class 1 integrons with the following gene cassette arrangements: dfrA1+aadA (6 strains) and dfrA17+aadA5 (7 strains). E. coli strains from food samples could represent a reservoir of ESBL-encoding genes and integrons that could be transmitted to humans through the food chain.
在突尼斯的不同超市和当地肉店采集的 79 份动物源食品样本中，研究了广谱头孢菌素耐药大肠杆菌分离株的存在及其耐药机制。这些样本中有 10 个（12.6%）含有产超广谱β-内酰胺酶（ESBL）的大肠杆菌分离株，共回收了 13 株 ESBL 阳性分离株（每个样本一个或两个），它们表现出 9 种不同的脉冲场凝胶电泳（PFGE）模式。检测到的 ESBL 如下：CTX-M-1（10 株）、CTX-M-1+TEM-1b（2 株）和 CTX-M-1+TEM-20（1 株）。在所有 13 株菌中，bla(CTX-M-1)基因下游均鉴定出 orf477 序列，9 株菌上游存在 ISEcp1。所有 ESBL 阳性株均归入 A 或 B1 组（分别为 4 株和 9 株）。79 份食品样本中有 3 份（3.8%）含有广谱头孢菌素耐药和 ESBL 阴性的大肠杆菌分离株，表现出 AmpC 表型。对每份样本中的一株菌进行了研究，发现它们的 PFGE 模式不相关。在这 3 株菌中的 1 株菌中鉴定出 CMY-2 型β-内酰胺酶，而在其余 2 株菌中检测到 ampC 基因启动子/衰减子区域的特定点突变（在-42、-18、-1 和+58 位置）。12 株 ESBL 阳性和 1 株 ESBL 阴性大肠杆菌菌株含有 1 类整合子，其基因盒排列如下：dfrA1+aadA（6 株）和 dfrA17+aadA5（7 株）。食品样本中的大肠杆菌菌株可能是 ESBL 编码基因和整合子的储存库，这些基因和整合子可能通过食物链传播给人类。
