Host-specific patterns of genetic diversity among IncI1 and IncK plasmids encoding CMY-2 β-lactamase in Escherichia coli isolates from humans, poultry meat, poultry and dogs in Denmark. IncI1 and IncK plasmids encoding CMY-2 β-lactamase

Objective: To elucidate the epidemiological pathways of CMY-2 β-lactamase transmission between animals and humans. Methods: Plasmid and strain relatedness was studied in 93 CMY-2-producing clinical and commensal Escherichia coli isolates collected in Denmark in 2006-2012 from humans, retail poultry meat, broilers and dogs. MLST, antimicrobial susceptibility testing and conjugation were performed in conjunction with plasmid replicon typing, pMLST, restriction fragment length polymorphism, and sequencing of selected plasmids harbouring blaCMY-2. Results: blaCMY-2 was detected on plasmids in 83 (89%) isolates. Most (75%) of these plasmids were conjugative and did not (96%) co-transfer resistance genes other than blaCMY-2. The main replicon types identified were IncI1 (55%) and IncK (39%). Isolates from different host species generally carried distinct plasmid subtypes with limited overlaps between species. Seven of the 18 human isolates harboured IncI1/ST2, IncI1/ST12 or IncK plasmids highly similar to those found among animal isolates, even though highly related human and animal plasmids differed by non-synonymous SNPs or insertion sequence elements and human isolates were more frequently resistant to non-β-lactams. MLST revealed high strain diversity except for E. coli ST38, which was identified in both Danish broiler chickens and broiler meat. Conclusion: This study clearly demonstrates that blaCMY-2 epidemiology can be understood only by thorough plasmid characterisation and provides useful baseline data to assess the consequences of the increasing human exposure to blaCMY-2 via contaminated meat. To date the spread of this β-lactam resistance determinant in Denmark is mainly associated to IncK and IncI1 plasmids that are generally distributed according to host-specific patterns.

研究目的：阐明CMY-2 β-内酰胺酶（CMY-2 β-lactamase）在动物与人类之间的传播流行病学路径。
研究方法：针对2006-2012年于丹麦采集的93株产CMY-2 β-内酰胺酶的临床及共生大肠埃希菌（Escherichia coli）分离株开展质粒与菌株亲缘性分析。上述分离株来源于人类、零售禽肉、肉鸡及犬只。本研究开展了多位点序列分型（MLST）、抗菌药物敏感性试验（antimicrobial susceptibility testing）、接合试验，联合质粒复制型分型、质粒多位点序列分型（pMLST）、限制性片段长度多态性分析，以及对携带blaCMY-2的部分质粒进行测序。
研究结果：83株（89%）分离株的质粒上检出blaCMY-2基因。其中75%的此类质粒可发生接合转移，且96%的质粒仅携带blaCMY-2这一种耐药基因。本研究鉴定到的主要质粒复制型为IncI1（55%）与IncK（39%）。不同宿主来源的分离株通常携带不同的质粒亚型，物种间重叠范围有限。18株人类来源分离株中有7株携带的IncI1/ST2、IncI1/ST12或IncK质粒与动物来源分离株中的质粒高度相似，尽管高度同源的人类与动物质粒存在非同义单核苷酸多态性（non-synonymous SNPs）或插入序列元件差异，且人类来源分离株对非β-内酰胺类抗菌药物的耐药率更高。多位点序列分型（MLST）结果显示菌株具有高度多样性，唯有大肠埃希菌ST38型同时在丹麦肉鸡及零售禽肉样本中被检出。
研究结论：本研究明确证实，唯有通过全面的质粒特征分析，才能阐明blaCMY-2的流行病学特征，并为评估人类通过受污染肉类持续暴露于blaCMY-2所带来的潜在风险提供了实用的基线数据。截至目前，丹麦境内该β-内酰胺类耐药决定因子的传播主要与IncK及IncI1型质粒相关，此类质粒通常呈现宿主特异性分布模式。