Sun Jisun, Yang My, Sreevatsan Srinand, Davies Peter R
Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, St. Paul, Minnesota, United States of America.
PLoS One. 2015 Nov 24;10(11):e0143670. doi: 10.1371/journal.pone.0143670. eCollection 2015.
A decade of research of methicillin-resistant S. aureus (MRSA) in pigs shows that the prevalence and predominant genotypes (i.e., ST398, ST9, ST5) of MRSA vary widely geographically, yet knowledge of the epidemiology of S. aureus generally in swine remains rudimentary. To characterize S. aureus, including MRSA, in the US swine industry, we sampled 38 swine herds in 11 states in major swine producing regions. The herds sampled included pigs sourced from 9 different breeding stock companies, and the sample was likely biased towards larger herds that use regular veterinary services. Twenty nasal swabs were collected from 36 groups of growing pigs by 36 swine veterinarians, 2 more herds were sampled opportunistically, and a historically MRSA-positive herd was included as a positive control. S. aureus was detected on 37 of the 38 herds, and in 77% of pigs sampled. Other than the positive control herd, no MRSA were detected in the study sample, yielding a 95% upper confidence limit of 9.3% for MRSA herd prevalence. All but two (ST1-t127; ST2007-t8314) of 1200 isolates belonged to three MLST lineages (ST9, ST398, and ST5) that have been prominent in studies of MRSA in pigs globally. A total of 35 spa types were detected, with the most prevalent being t337 (ST9), t034 (ST398), and t002 (ST5). A purposively diverse subset of 128 isolates was uniformly negative on PCR testing for major enterotoxin genes. The findings support previous studies suggesting a relatively low herd prevalence of MRSA in the US swine industry, but confirm that methicillin susceptible variants of the most common MRSA genotypes found in swine globally are endemic in the US. The absence of enterotoxin genes suggests that the source of toxigenic S. aureus capable of causing foodborne enterotoxicosis from pork products is most likely post-harvest contamination.
对猪体内耐甲氧西林金黄色葡萄球菌（MRSA）长达十年的研究表明，MRSA的流行率和主要基因型（即ST398、ST9、ST5）在地理上差异很大，但总体而言，猪体内金黄色葡萄球菌的流行病学知识仍很基础。为了描述美国养猪业中包括MRSA在内的金黄色葡萄球菌特征，我们在主要生猪产区的11个州对38个猪群进行了采样。所采样的猪群包括来自9家不同种猪公司的猪，且样本可能偏向于使用常规兽医服务的大型猪群。36名猪兽医从36组生长猪中采集了20份鼻拭子，另外对2个猪群进行了机会性采样，并将一个历史上MRSA呈阳性的猪群作为阳性对照。在38个猪群中的37个检测到了金黄色葡萄球菌，且在77%的采样猪中检测到该菌。除阳性对照猪群外，研究样本中未检测到MRSA，MRSA猪群流行率的95%置信上限为9.3%。1200株分离株中，除两株（ST1-t127；ST2007-t8314）外，其余均属于三个多位点序列分型谱系（ST9、ST398和ST5），这些谱系在全球猪MRSA研究中很突出。共检测到35种spa型，最常见的是t337（ST9）、t034（ST398）和t002（ST5）。对128株分离株进行的一个有目的的多样化子集在主要肠毒素基因的PCR检测中均为阴性。这些发现支持了先前的研究，表明美国养猪业中MRSA的猪群流行率相对较低，但证实了全球猪中最常见的MRSA基因型的甲氧西林敏感变体在美国是地方性流行的。肠毒素基因的缺失表明，能够导致猪肉制品食源性肠毒素中毒的产毒素金黄色葡萄球菌的来源很可能是收获后的污染。
