Meloni Domenico, Galluzzo Pietro, Mureddu Anna, Piras Francesca, Griffiths Mansel, Mazzette Rina
Department of Animal Biology, Faculty of Veterinary Medicine, University of Sassari, Via Vienna 2, 07100, Sassari, Italy.
Int J Food Microbiol. 2009 Feb 15;129(2):166-73. doi: 10.1016/j.ijfoodmicro.2008.11.014. Epub 2008 Nov 18.
The aims of the present study were: (a) to investigate the prevalence and the enumeration of Listeria monocytogenes in 200 samples of ready to eat (RTE) foods of animal and vegetal origin collected from different outlets and processing plants in Sardinia; (b) to characterize the isolates by phenotypical and molecular methods; (c) to analyze a subset of 42 L. monocytogenes by automated EcoRI ribotyping in order to predict the strain's potential virulence for humans. The strains were isolated from: smoked fish products, cooked marinated products, meat products and pre-packaged mixed vegetable salads. Of the samples tested, 22% were positive for Listeria spp. The prevalence of L. monocytogenes was 9.5%, while the level of L. monocytogenes in the positive samples was <10 cfu/g in 94.7% of cases. EcoRI ribotyping differentiated the isolates into 16 distinct ribotypes (similarity>93%), belonging to 17 different DuPont Identification Library Codes (DUP-IDs) clones. The Simpson's numerical index of discrimination was 0.911. Cluster analysis pointed out a high similarity among strains isolated from meat, fish, and vegetables of different origin. These results confirmed the existence of a widespread population of L. monocytogenes, characterized by highly related strains existing in different geographical areas. 65% of these strains belonged to lineage II (serotypes 1/2a and 1/2c), subtypes known to be associated with sporadic human listeriosis outbreaks. The remaining 35% of the isolates (serotypes 1/2b, 3b and 4b) were allocated to lineage I and belong to distinct clonal groups (DUP-ID 1038 and 1042), which again have been associated with several outbreaks of human listeriosis. Neither atypical profiles nor lineage III strains were found. EcoRI ribotyping was confirmed as a rapid and reliable method for L. monocytogenes typing, providing useful data for epidemiologic and clonality surveys of L. monocytogenes strains isolated from RTE foods.
(a)调查从撒丁岛不同销售点和加工厂采集的200份动植物源性即食(RTE)食品样本中单核细胞增生李斯特菌的流行情况和计数；(b)通过表型和分子方法对分离株进行特征分析；(c)通过自动EcoRI核糖分型分析42株单核细胞增生李斯特菌的一个子集，以预测菌株对人类的潜在毒力。这些菌株分离自：烟熏鱼制品、熟腌制品、肉制品和预包装混合蔬菜沙拉。在检测的样本中，22%的样本李斯特菌属呈阳性。单核细胞增生李斯特菌的流行率为9.5%，而在阳性样本中，94.7%的情况下单核细胞增生李斯特菌的水平<10 cfu/g。EcoRI核糖分型将分离株分为16种不同的核糖型(相似度>93%)，属于17种不同的杜邦鉴定文库编码(DUP-IDs)克隆。辛普森数值鉴别指数为0.911。聚类分析指出，从不同来源的肉类、鱼类和蔬菜中分离出的菌株之间具有高度相似性。这些结果证实了广泛存在的单核细胞增生李斯特菌群体的存在，其特征是不同地理区域存在高度相关的菌株。这些菌株中有65%属于II系(血清型1/2a和1/2c)，已知这些亚型与散发性人类李斯特菌病暴发有关。其余35%的分离株(血清型1/2b、3b和4b)被归入I系，属于不同的克隆群(DUP-ID 1038和1042)，这些克隆群也与几起人类李斯特菌病暴发有关。未发现非典型图谱或III系菌株。EcoRI核糖分型被确认为一种快速可靠的单核细胞增生李斯特菌分型方法，为从即食食品中分离的单核细胞增生李斯特菌菌株的流行病学和克隆性调查提供了有用的数据。
