Division of Microbiology, National Center for Toxicological Research, US Food and Drug Administration, Jefferson, Arkansas 72079, USA.
Antimicrob Agents Chemother. 2011 Dec;55(12):5666-75. doi: 10.1128/AAC.00656-11. Epub 2011 Sep 26.
Resistance to extended-spectrum cephalosporins (ESC) among members of the family Enterobacteriaceae occurs worldwide; however, little is known about ESC resistance in Escherichia coli strains from companion animals. Clinical isolates of E. coli were collected from veterinary diagnostic laboratories throughout the United States from 2008 to 2009. E. coli isolates (n = 54) with reduced susceptibility to ceftazidime or cefotaxime (MIC ≥ 16 μg/ml) and extended-spectrum-β-lactamase (ESBL) phenotypes were analyzed. PCR and sequencing were used to detect mutations in ESBL-encoding genes and the regulatory region of the chromosomal gene ampC. Conjugation experiments and plasmid identification were conducted to examine the transferability of resistance to ESCs. All isolates carried the bla(CTX-M-1)-group β-lactamase genes in addition to one or more of the following β-lactamase genes: bla(TEM), bla(SHV-3), bla(CMY-2), bla(CTX-M-14-like), and bla(OXA-1.) Different bla(TEM) sequence variants were detected in some isolates (n = 40). Three isolates harbored a bla(TEM-181) gene with a novel mutation resulting in an Ala184Val substitution. Approximately 78% of the isolates had mutations in promoter/attenuator regions of the chromosomal gene ampC, one of which was a novel insertion of adenine between bases -28 and -29. Plasmids ranging in size from 11 to 233 kbp were detected in the isolates, with a common plasmid size of 93 kbp identified in 60% of isolates. Plasmid-mediated transfer of β-lactamase genes increased the MICs (≥ 16-fold) of ESCs for transconjugants. Replicon typing among isolates revealed the predominance of IncI and IncFIA plasmids, followed by IncFIB plasmids. This study shows the emergence of conjugative plasmid-borne ESBLs among E. coli strains from companion animals in the United States, which may compromise the effective therapeutic use of ESCs in veterinary medicine.
肠杆菌科家族成员对扩展谱头孢菌素（ESC）的耐药性在全球范围内普遍存在；然而，关于伴侣动物来源的大肠杆菌菌株对 ESC 的耐药性知之甚少。2008 年至 2009 年，从美国各地的兽医诊断实验室收集了临床分离的大肠杆菌。分析了对头孢他啶或头孢噻肟（MIC≥16μg/ml）和超广谱β-内酰胺酶（ESBL）表型具有较低敏感性的大肠杆菌分离株（n=54）。使用 PCR 和测序检测 ESBL 编码基因和染色体基因 ampC 的调节区的突变。进行了接合实验和质粒鉴定，以检查对 ESC 耐药性的可转移性。所有分离株均携带 bla(CTX-M-1)-组β-内酰胺酶基因，此外还携带一种或多种以下β-内酰胺酶基因：bla(TEM)、bla(SHV-3)、bla(CMY-2)、bla(CTX-M-14-like)和 bla(OXA-1)。在一些分离株中检测到不同的 bla(TEM)序列变体（n=40）。三种分离株携带 bla(TEM-181)基因，该基因具有导致 Ala184Val 取代的新突变。大约 78%的分离株在染色体基因 ampC 的启动子/衰减子区域有突变，其中一个突变是在碱基-28 和-29 之间插入腺嘌呤。在分离株中检测到大小为 11 至 233 kbp 的质粒，其中 60%的分离株中鉴定出一种常见的 93 kbp 大小的质粒。β-内酰胺酶基因的质粒介导转移使转导子对 ESC 的 MIC（≥16 倍）增加。分离株中的复制子分型显示 IncI 和 IncFIA 质粒占主导地位，其次是 IncFIB 质粒。这项研究表明，美国伴侣动物来源的大肠杆菌菌株中出现了可转移的质粒介导的 ESBL，这可能会影响 ESC 在兽医医学中的有效治疗用途。
