College of Light Industry and Food Sciences, South China University of Technology, 510640 Guangzhou, China.
Int J Food Microbiol. 2010 Dec 15;144(2):310-6. doi: 10.1016/j.ijfoodmicro.2010.10.015. Epub 2010 Nov 11.
A total of 2177 food samples collected from nine cities in northern China during 2005 to 2007 were screened for the presence of Listeria monocytogenes. All L. monocytogenes isolates were subjected to serotyping, antimicrobial susceptibility, pulsed-field gel electrophoresis (PFGE), as well as PCR screening to identify genes responsible for tetracycline resistance [tet(L), tet(M), tet(K), tet(S) and tet(B)], transposon Tn916, and class 1 integron. Contamination with L. monocytogenes was detected in 4.13% (90/2177) of the total samples representing various food products. The pathogen was mainly isolated from frozen food made of wheat flour or rice products (26/252, 10.32%) and raw meat products (46/733, 6.28%). Besides, 3.31% (10/302) of cooked meat, 1.17% (4/343) of seafood, 0.98% (2/204) of non-fermented bean products and 0.62% (2/323) of vegetables samples were contaminated by this bacterium. The L. monocytogenes isolates belonged to five serotypes (1/2a, 1/2b, 1/2c, 4b, and 3a), with serotype 1/2a being dominant (48.88%). Antimicrobial resistance was most frequently observed for ciprofloxacin (17.8%), tetracycline (15.6%) and streptomycin (12.2%). Overall, resistance was observed against 14 out of 18 antimicrobials tested while multiple resistances occurred among 18.9% (17/90) isolates. Interestingly, two isolates were resistant to more than five antimicrobials. Among 14 tetracycline-resistant isolates, 13 carried tet(M) gene including nine possessing Tn916, and one harbored tet(S) gene. PFGE analysis revealed genetic heterogeneity among individual serotypes as well as scattered occurrence of some genotypes without any clear-cut correlation to source or food type. The widespread distribution of epidemiologically important serotypes (1/2a, 1/2b and 4b) of L. monocytogenes, and their resistance to commonly used antibiotics indicate a potential public health risk. Our data also indicate that L. monocytogenes could act as a reservoir of mobile tet genes along the food chain.
从中国北方九个城市于 2005 年至 2007 年采集的 2177 份食品样本中筛选出李斯特菌。所有李斯特菌分离株均进行血清分型、药敏试验、脉冲场凝胶电泳（PFGE）以及 PCR 筛选，以鉴定四环素耐药基因 [tet(L)、tet(M)、tet(K)、tet(S) 和 tet(B)]、转座子 Tn916 和 class 1 整合子。在代表各种食品的 2177 份总样本中，检测到李斯特菌污染的比例为 4.13%（90/2177）。该病原体主要从由小麦粉或大米产品制成的冷冻食品（26/252，10.32%）和生肉产品（46/733，6.28%）中分离出来。此外，熟食肉（3.31%，10/302）、海鲜（1.17%，4/343）、非发酵豆制品（0.98%，2/204）和蔬菜样本（0.62%，2/323）也受到该细菌的污染。李斯特菌分离株属于五个血清型（1/2a、1/2b、1/2c、4b 和 3a），其中血清型 1/2a 占优势（48.88%）。最常观察到的抗生素耐药性是环丙沙星（17.8%）、四环素（15.6%）和链霉素（12.2%）。总体而言，在所测试的 18 种抗生素中，有 14 种显示出耐药性，而 18.9%（17/90）的分离株则出现了多种耐药性。有趣的是，有两个分离株对超过五种抗生素具有耐药性。在 14 株四环素耐药株中，13 株携带 tet(M)基因，其中 9 株带有 Tn916，1 株携带 tet(S)基因。PFGE 分析显示，不同血清型之间存在遗传异质性，以及某些基因型的分散发生，与来源或食品类型没有任何明确的关联。具有重要流行病学意义的李斯特菌血清型（1/2a、1/2b 和 4b）的广泛分布及其对常用抗生素的耐药性表明存在潜在的公共卫生风险。我们的数据还表明，李斯特菌可能是食物链中移动 tet 基因的储存库。
