进口水产品中单增李斯特菌的分子流行病学特点

摘要：目的] 探明进口水产品中单增李斯特菌的污染状况、致病性和分子特征。方法] 针对2007年7月至2008年11月间从29个国家进口的1275批水产品，进行单增李斯特菌鉴定、谱系与血清型分析、小鼠毒力试验与多位点序列分析。结果] 检出单增李斯特菌33批次（2.6%），其中以4b型为主（65.2%），而1/2a型、1/2b型与1/2c型仅分别占13.0%、17.4%与4.4%。这些分离株对小鼠均具有与强毒参考株相当的毒力。基于actA-hisJ-ribC-sigB的多位点序列分析可将32个菌株分为23个序列型，分辨力达0.97。其中3个序列型包含3个以上分离株，其中序列型9属于流行性克隆I。结论] 进口水产品中单增李斯特菌污染率与国内水产品相近，但血清型分布以4b型为主，且有流行性克隆I检出，因此要加强对进口水产品中单增李斯特菌的监测。

Molecular epidemiology of Listeria monocytogenes isolates from imported fishery products to China

Abstract: Objective] We examined the prevalence, molecular characteristics and virulence potential of Listeria monocytogenes isolates from imported fishery products to gain further insights on the public health risk caused by this important food borne pathogen. Methods] L. monocytogenes isolates, screened from 1275 batches of fishery products imported from July 2007 to November 2008, were studied by lineage classification, serotyping, in vivo virulence assessment in ICR mouse model and multilocus sequence typing (MLST). Results] Thirty-three batches were contaminated by L. monocytogenes (33/1275, 2.6%), in which serovar 4b dominated (65.2%), followed by serovars 1/2b (17.4%), 1/2a (13.0%) and 1/2c (4.4%). These isolates were all as virulent as L. monocytogenes reference strains. Of 23 selected L. monocytogenes isolates and 9 reference strains, 23 sequence types (STs) were recognized with discrimination index (D.I.) of 0.97, based on the concatenated gene cluster covering one virulent gene actA, two housekeeping genes hisJ and ribC, and one stress-response gene sigB. Remarkably, 3 isolates from American salmon, Argentina squid and Peru squid respectively belonged to ST9 which represented epidemic clone I (ECI). The isolation rate of L. monocytogenes in imported fishery products (2.6%) was similar to that in domestic fishery products (2.7%). Serovar 4b, which was more virulent than other serovars in humans, was dominant in imported fishery products, and even ECI was recognized. Conclusion] All of these isolates were as virulent as L. monocytogenes reference strains, suggesting inspection and quarantine strategies of imported fishery products should be strengthened effectively.