云南省牛乳中单核细胞增生李斯特氏菌的分布特征、耐药性及毒力研究

Distribution characteristics, drug resistance and virulence of Listeria monocytogenes in milk in Yunnan province

中文关键词:  牛乳  单核细胞增生李斯特氏菌  耐药性  毒力基因

英文关键词:milk  Listeria monocytogenes  drug resistance  virulence genes

中文摘要:

      目的 分析云南省牛乳中单核细胞增生李斯特氏菌(Listeria monocytogenes)的分布特征、耐药性及毒力现状。方法 采集云南省主要奶产区牛乳样本, 按照GB 4789.30—2016方法分离单核细胞增生李斯特氏菌疑似菌株, 采用飞行时间质谱技术结合16S rDNA测序对疑似菌株进行鉴定; 采用微量肉汤稀释法对分离菌株进行抗生素药敏实验; 通过聚合酶链式反应(polymerase chain reaction, PCR)技术检测单核细胞增生李斯特氏菌中7种毒力基因的存在状况。结果 158份样品共有4份检出单核细胞增生李斯特氏菌, 检出率为2.53%; 共分离获得8株菌。其中, 生鲜乳中检出率为3.36%, 巴氏杀菌乳中未检出。在生鲜乳中, 荷斯坦牛乳、水牛乳、牦牛乳检出率分别为2.13%、0.00%和20.00%; 标准化牛场、奶牛合作社和个体户的检出率分别为2.50%、1.51%和15.38%; 手工挤奶和机械挤奶检出率为11.76%和1.96%。药敏实验结果显示8株菌均对青霉素耐药, 对四环素、复方新诺明、红霉素耐药率分别为87.50%、75.00%和50.00%; 多重耐药率为75.00%; 但所有菌株对氨苄西林均敏感。8株菌对7种毒力基因的携带程度从12.50%~75.00%不等。结论 云南省牛乳尤其生鲜乳中存在一定程度的单核细胞增生李斯特氏菌污染, 且该菌具有普遍耐药性并携带一定程度的毒力基因, 对消费者的安全具有潜在风险, 应加强卫生监督管理。

英文摘要:

      Objective To analyze the distribution characteristics, drug resistance and virulence of Listeria monocytogenes in the milk of Yunnan province. Methods Collected milk samples from major milk producing areas in Yunnan province, and isolated suspected Listeria monocytogenes strains according to GB 4789.30—2016 method, and time-of-flight mass spectrometry technology combined with 16S rDNA sequencing was used to identify the suspected strains. Antibiotic susceptibility test was performed by micro broth dilution method on the isolated strains, and polymerase chain reaction (PCR) technology was used to detect the existence of 7 virulence genes in Listeria monocytogenes. Results Listeria monocytogenes were detected in four of the 158 samples. The detection rate was 2.53%; eight strains were isolated. Among them, the detection rate in raw milk was 3.36%, and it was not detected in pasteurized milk. In raw milk, the detection rates of Holstein milk, buffalo milk, and yak milk were 2.13%, 0.00% and 20.00%, respectively; the detection rates of standardized cattle farms, dairy cooperatives, and self-employed were 2.50%, 1.51% and 15.38%, the detection rates of manual milking and mechanical milking were 11.76% and 1.96%. The drug sensitivity results showed that eight strains were resistant to penicillin. Their resistance rates to tetracycline, compound trimethoprim and erythromycin were 87.50%, 75.00%, and 50.00%, respectively, and their multi-drug resistance rate was 75.00%. But all strains were sensitive to ampicillin. The seven virulence genes were distributed in different degrees in eight strains, ranging from 12.50% to 75.00%. Conclusion There is a certain degree of L. monocytogenes contamination in milk in Yunnan province, especially raw milk. Moreover, these L. monocytogenes strains from milk have universal drug resistance and carry a certain degree of virulence genes, which have potential risks to the safety of consumers. Therefore, the health supervision and management of milk should be strengthened.