Department of Veterinary Preventive Medicine, College of Veterinary Medicine, Ohio State University, Columbus, Ohio, USA.
J Clin Microbiol. 2012 Nov;50(11):3687-93. doi: 10.1128/JCM.01971-12. Epub 2012 Sep 12.
The main goal of this study was to determine the prevalence of methicillin-resistant Staphylococcus aureus (MRSA), particularly livestock-associated MRSA (LA-MRSA) in pigs and pork. The genotypic relatedness of isolates on the farm, at slaughter, and at the retail level was assessed. Paired nasal and perianal swab samples were collected from 10 cohorts of market-age pigs (24 pigs per cohort) and carcasses at slaughterhouse, and pork samples were collected at retail. Staphylococci were isolated using selective enrichment method. Isolates were tested for antimicrobial resistance by broth microdilution. Duplex PCR was used to confirm MRSA using species-specific (nuc) and methicillin resistance (mecA) genes. The clonal relatedness of isolates was determined using pulsed-field gel electrophoresis (PFGE), Staphylococcus protein A (spa) typing, multilocus sequence typing (MLST), and staphylococcal cassette chromosome mec element (SCCmec) typing. MRSA was detected in 5 of the 10 cohorts (50%), with the prevalence ranging from 0% to 12.5% per cohort. Of all the pigs sampled on the farm before they went to market, 3% (7/240) were MRSA positive. A higher prevalence of MRSA was detected at holding pens at the slaughterhouse (11% [27/240]). MRSA was also detected in 2% (4/235) of the carcasses and 4% (5/135) of the retail pork. While the isolates appear predominantly to be highly clonal, PFGE had a relatively higher discriminatory power (discriminatory index [DI] = 0.624). Four genotypic clusters were identified by PFGE; of the four clusters, clonal type B was predominant across the farm-to-retail continuum. MLST findings revealed that sequence type 5 (ST5) was the most predominant subtype (32/50). The livestock-associated MRSA (clonal complex 398 [CC398] or sequence type 398 [ST398]) was the second common type (12/50) and was detected at all stages from farm to retail. Nine of the 50 (18%) MRSA isolates belonged to spa type 539/t034 that were of ST398 based on MLST. The results of this study confirm that MRSA, including LA-MRSA, is common in herds of swine in Ohio and hereby shown to persist in the farm to processing and retail continuum.
本研究的主要目的是确定耐甲氧西林金黄色葡萄球菌（MRSA），特别是与牲畜相关的耐甲氧西林金黄色葡萄球菌（LA-MRSA）在猪和猪肉中的流行情况。评估了农场、屠宰场和零售层面分离株的基因型相关性。从 10 组市场年龄猪（每组 24 头猪）和屠宰场的屠宰猪以及零售的猪肉中采集鼻和肛周配对拭子样本。使用选择性富集方法分离葡萄球菌。使用肉汤微量稀释法测试分离物的抗微生物药物耐药性。使用种特异性（nuc）和甲氧西林耐药（mecA）基因的双重 PCR 确认 MRSA。使用脉冲场凝胶电泳（PFGE）、葡萄球菌蛋白 A（spa）分型、多位点序列分型（MLST）和葡萄球菌盒式染色体 mec 元件（SCCmec）分型确定分离株的克隆相关性。在 10 组中的 5 组（50%）中检测到 MRSA，每个组的流行率为 0%至 12.5%。在上市前进入市场的所有猪中，有 3%（7/240）为 MRSA 阳性。在屠宰场的畜栏中检测到更高的 MRSA 患病率（11%[27/240]）。在 2%（4/235）的胴体和 4%（5/135）的零售猪肉中也检测到了 MRSA。虽然分离株主要表现出高度的克隆性，但 PFGE 的分辨力相对较高（分辨指数[DI] = 0.624）。通过 PFGE 鉴定了 4 个基因簇；在这 4 个簇中，B 型克隆在从农场到零售的连续体中占主导地位。MLST 结果表明，序列类型 5（ST5）是最主要的亚型（32/50）。与牲畜相关的 MRSA（克隆复合体 398 [CC398]或序列类型 398 [ST398]）是第二种常见类型（12/50），并在从农场到零售的各个阶段都有检测到。50 株 MRSA 分离株中的 9 株（18%）属于 spa 型 539/t034，根据 MLST 属于 ST398。本研究结果证实，耐甲氧西林金黄色葡萄球菌，包括与牲畜相关的耐甲氧西林金黄色葡萄球菌，在俄亥俄州的猪群中很常见，并证明其在从农场到加工和零售的连续体中持续存在。
