Kim S-H, Wei C-I
Department of Nutrition and Food Science, University of Maryland, College Park, MD 20742, USA.
J Appl Microbiol. 2007 Aug;103(2):400-8. doi: 10.1111/j.1365-2672.2006.03255.x.
To better understand antibiotic resistance of Enterobacter cloacae isolates originated from food animals, the phenotypic and genotypic resistance of Ent. cloacae isolates from retail ground beef, cattle farm, processing facilities and clinical settings were investigated.
The ampC, ampD and ampR genes in the isolates were sequenced and analysed. beta-Lactamase activities and beta-lactamase profiles of the isolates were analysed by the enzymatic hydrolysis of nitrocefin and isoelectric focussing, respectively. The ampC gene of the Ent. cloacae isolate was cloned and transformed into Escherichia coli strains. The genomic DNA profiles of Ent. cloacae isolates were analysed by using pulse field gel electrophoresis (PFGE). Mutation at one residue (Val-54-->Ile) in the AmpR amino acid sequence was consistently found in Ent. cloacae isolates that were resistant to a broadspectrum of beta-lactam agents. The enzyme activity in the isolates was induced by cefoxitin. The pI (isoelectric point) of the enzymes produced by the test strains ranged from 8.4 to 8.9. Cloning of ampC gene of the Ent. cloacae isolate conferred the resistance to ampicillin, cephalothin and amoxicillin in recipient E. coli strains. One recipient of E. coli O157:H7 strain additionally acquired resistance to ceftiofur. The genomic analysis of Ent. cloacae isolates by PFGE showed that the isolates from various sources were genetically unrelated.
The spread of diverse clones of AmpC-producing Ent. cloacae occurred in the ecosystem and retail products.
Our findings suggested that AmpC-producing Ent. cloacae could be a contributor in spreading beta-lactamase genes in farm environments and food processing environments.
为了更好地了解源自食用动物的阴沟肠杆菌分离株的抗生素耐药性，对来自零售绞碎牛肉、养牛场、加工设施及临床环境的阴沟肠杆菌分离株进行了表型和基因型耐药性研究。
对分离株中的ampC、ampD和ampR基因进行测序和分析。分别通过硝基头孢菌素的酶促水解和等电聚焦分析分离株的β-内酰胺酶活性及β-内酰胺酶谱。克隆阴沟肠杆菌分离株的ampC基因并将其转化到大肠杆菌菌株中。使用脉冲场凝胶电泳（PFGE）分析阴沟肠杆菌分离株的基因组DNA图谱。在对多种β-内酰胺类药物耐药的阴沟肠杆菌分离株中始终发现AmpR氨基酸序列中的一个残基（Val-54→Ile）发生了突变。分离株中的酶活性由头孢西丁诱导。测试菌株产生的酶的pI（等电点）范围为8.4至8.9。阴沟肠杆菌分离株ampC基因的克隆使受体大肠杆菌菌株对氨苄西林、头孢噻吩和阿莫西林产生耐药性。一株大肠杆菌O157:H7受体菌株还额外获得了对头孢噻呋的耐药性。通过PFGE对阴沟肠杆菌分离株进行的基因组分析表明，来自不同来源的分离株在基因上不相关。
产AmpC阴沟肠杆菌的不同克隆在生态系统和零售产品中传播。
我们的研究结果表明，产AmpC阴沟肠杆菌可能是在农场环境和食品加工环境中传播β-内酰胺酶基因的一个因素。
