1 Research Group of Bacterial Genomics and Antimicrobial Resistance, National Food Institute, Technical University of Denmark , Lyngby, Denmark .
Foodborne Pathog Dis. 2014 Sep;11(9):740-6. doi: 10.1089/fpd.2014.1742. Epub 2014 Jun 27.
This study investigated the occurrence of extended spectrum cephalosporinase (ESC)-producing Escherichia coli in a broiler production with no cephalosporin use and a low use of antimicrobials in general. Furthermore, it investigated whether the current consumption of aminopenicillins selects for ESC-producing E. coli and whether certain clones or plasmids spread from imported parent flocks to the meat.
ESC-producing E. coli was isolated using MacConkey broth with 1 mg/L of ceftriaxone. ESC genes were identified using polymerase chain reaction and sequencing. Isolates with blaCMY-2 were subtyped by pulsed-field gel electrophoresis (PFGE), phylotyping, and antimicrobial susceptibility testing. Selected isolates were used as donors in filter-mating experiments, multilocus sequence typing (MLST), and plasmid replicons were typed. Aminopenicillin use at the farm (not flock) level was obtained from VetStat, a database for mandatory registration of veterinary prescriptions in Denmark.
ESC-producing E. coli occurred in 93% (27/29) of broiler parent farms in 2011, 27% (53/197) of broiler flocks in 2010, and 3.3% (4/121) of Danish retail broiler meat in 2009 and 8.6% (16/187) in 2010. The ESC producing E. coli contained blaCMY-2, blaSHV-2 or blaCTX-M-1. Isolates with blaCMY-2 represented 35 PFGE groups. One group dominated (39 isolates) and included isolates with indistinguishable PFGE patterns from parents, broilers, and meat. Most blaCMY-2 isolates were susceptible to non-β-lactams, and blaCMY-2 was mostly present on horizontally transferable incI1 or incK plasmids. Phylogroup D was most common and E. coli MLST types previously found in humans were observed. Broiler farms with registered aminopenicillin use had significantly higher occurrence of ESC E. coli.
ESC-producing E. coli from flocks of imported broiler parents spread clonally and horizontally to broiler meat (including potentially human pathogenic types) even in a country with no cephalosporin use. Use of aminopenicillins may influence the persistence of ESC-producing E. coli in the broiler production, but other factors should be investigated.
本研究调查了在未使用头孢菌素且普遍较少使用抗生素的肉鸡生产中，产超广谱头孢菌素酶（ESC）的大肠杆菌的发生情况。此外，本研究还调查了目前使用氨苄西林是否会选择产 ESC 的大肠杆菌，以及某些克隆或质粒是否会从进口的亲代鸡群传播到鸡肉中。
使用含有 1mg/L 头孢曲松的麦康凯肉汤分离产 ESC 的大肠杆菌。使用聚合酶链反应和测序鉴定 ESC 基因。对携带 blaCMY-2 的分离株进行脉冲场凝胶电泳（PFGE）、系统发育分型和药敏试验分型。选择的分离株用作过滤交配实验、多位点序列分型（MLST）和质粒复制子的供体。农场（而非鸡群）水平的氨苄西林使用情况从 VetStat 获得，这是丹麦强制性兽医处方登记数据库。
2011 年，27/29 个肉鸡亲代农场、2010 年 197 个肉鸡鸡群、2009 年 121 个丹麦零售肉鸡肉和 2010 年 187 个肉鸡肉中出现产 ESC 的大肠杆菌分别占 93%（27/29）、27%（53/197）、3.3%（4/121）和 8.6%（16/187）。产 ESC 的大肠杆菌含有 blaCMY-2、blaSHV-2 或 blaCTX-M-1。携带 blaCMY-2 的分离株代表了 35 个 PFGE 群。其中一个群占主导地位（39 个分离株），包括与亲本、肉鸡和肉中分离出的不可区分的 PFGE 模式的分离株。大多数 blaCMY-2 分离株对非β-内酰胺类药物敏感，blaCMY-2 主要存在于可水平转移的 incI1 或 incK 质粒上。D 群最常见，观察到与人相关的大肠杆菌 MLST 类型。有登记氨苄西林使用的肉鸡养殖场产 ESC 的大肠杆菌发生率显著更高。
即使在没有头孢菌素使用的国家，来自进口肉鸡亲代鸡群的产 ESC 的大肠杆菌也通过克隆和水平传播到肉鸡肉（包括潜在的人病原类型）。氨苄西林的使用可能会影响 ESC 产生的大肠杆菌在肉鸡生产中的持续存在，但还需要调查其他因素。
