Ryser E T, Arimi S M, Bunduki M M, Donnelly C W
Department of Animal and Food Sciences, University of Vermont, Burlington 05405, USA.
Appl Environ Microbiol. 1996 May;62(5):1781-7. doi: 10.1128/aem.62.5.1781-1787.1996.
Isolation rates for Listeria monocytogenes and the other Listeria spp. typically improve when samples are enriched in more than one primary enrichment medium. This study evaluated the abilities of two primary enrichment media, University of Vermont-modified Listeria enrichment broth (UVM) and Listeria repair broth (LRB), to recover different ribotypes of Listeria spp. from raw meat and poultry samples. Forty-five paired 25-g retail samples of ground beef, pork sausage, ground turkey, and chicken (160 samples) underwent primary enrichment in UVM and LRB (30 degrees C for 24 h) followed by secondary enrichment in Fraser broth (35 degrees C for 24 and 40 h) and plating on modified Oxford agar. After 24 h of incubation of 35 degrees C, 608 Listeria colonies from selected positive samples were biochemically confirmed as L. monocytogenes (245 isolates), L innocua (276 isolates), and L. welshimeri (89 isolates) and then ribotyped with the automated Riboprinter microbial characterization system (E. I. du Pont de Nemours & Co., Inc.). Thirty-six different Listeria strains comprising 16 L. monocytogenes (including four known clinical ribotypes), 12 L. innocua, and 8 L. welshimeri ribotypes were identified from selected positive samples (15 samples of each product type; two UVM and two LRB isolates per sample). Twenty-six of 36(13 L. monocytogenes) ribotypes were detected with both UVM and LRB, whereas 3 of 36 (1 L. monocytogenes) and 7 of 36 (3 L. monocytogenes) Listeria ribotypes were observed with only UVM or LRB, respectively. Ground beef, pork sausage, ground turkey, and chicken yielded 22 (8 L. monocytogenes), 21 (12 L. monocytogenes), 20 (9 L. monocytogenes), and 19 (11 L. monocytogenes) different Listeria ribotypes, respectively, with some Listeria ribotypes confined to a particular product. More importantly, major differences in both the number and distribution of Listeria ribotypes, including previously recognized clinical and nonclinical ribotypes of L. monocytogenes, were observed when 10 UVM and 10 LRB isolates from five samples of each product were ribotyped. When a third set of six samples per product type was examined from which two Listeria isolates were obtained by using only one of the two primary enrichment media, UVM and LRB failed to detect L. monocytogenes (both clinical and nonclinical ribotypes) in two and four samples, respectively. These findings stress the importance of using more than one primary enrichment medium and picking a sufficient number of colonies per sample when attempting to isolate specific L. monocytogenes strains during investigations of food-borne listeriosis.
当样本在不止一种初级富集培养基中进行富集时，单核细胞增生李斯特菌和其他李斯特菌属的分离率通常会提高。本研究评估了两种初级富集培养基，即佛蒙特大学改良李斯特菌富集肉汤（UVM）和李斯特菌修复肉汤（LRB），从生肉和禽肉样本中回收不同核糖型李斯特菌属的能力。45对25克的碎牛肉、猪肉香肠、碎火鸡肉和鸡肉零售样本（共160个样本）先在UVM和LRB中进行初级富集（30℃培养24小时），然后在弗雷泽肉汤中进行二级富集（35℃培养24小时和40小时），并接种于改良牛津琼脂平板上。在35℃培养24小时后，从选定的阳性样本中获得的608个李斯特菌菌落经生化鉴定为单核细胞增生李斯特菌（245株分离株）、无害李斯特菌（276株分离株）和威氏李斯特菌（89株分离株），然后使用自动核糖分型微生物鉴定系统（E.I.杜邦公司）进行核糖分型。从选定的阳性样本（每种产品类型15个样本；每个样本2株UVM和2株LRB分离株）中鉴定出36种不同的李斯特菌菌株，包括16种单核细胞增生李斯特菌（包括4种已知的临床核糖型）、12种无害李斯特菌和8种威氏李斯特菌核糖型。36种核糖型中的26种（13种单核细胞增生李斯特菌）在UVM和LRB中均被检测到，但36种中的3种（1种单核细胞增生李斯特菌）和36种中的7种（3种单核细胞增生李斯特菌）核糖型分别仅在UVM或LRB中被观察到。碎牛肉、猪肉香肠、碎火鸡肉和鸡肉分别产生了22种（8种单核细胞增生李斯特菌）、21种（12种单核细胞增生李斯特菌）、20种（9种单核细胞增生李斯特菌）和19种（11种单核细胞增生李斯特菌）不同的李斯特菌核糖型，一些李斯特菌核糖型局限于特定产品类型。更重要的是，当对每种产品的5个样本中的10株UVM和10株LRB分离株进行核糖分型时，观察到李斯特菌核糖型在数量和分布上的主要差异，包括先前确认的单核细胞增生李斯特菌的临床和非临床核糖型。当对每种产品类型的第三组6个样本进行检测时，通过仅使用两种初级富集培养基之一（UVM和LRB）从每个样本中获得2株李斯特菌分离株，UVM和LRB分别在2个和4个样本中未能检测到单核细胞增生李斯特菌（临床和非临床核糖型）。这些发现强调了在食源性李斯特菌病调查中，使用不止一种初级富集培养基并从每个样本中挑选足够数量菌落以分离特定单核细胞增生李斯特菌菌株的重要性。
