Department of Food Science, University of Wisconsin, Madison 53706.
Department of Food Science, University of Wisconsin, Madison 53706.
J Dairy Sci. 2021 Apr;104(4):4561-4574. doi: 10.3168/jds.2020-18885. Epub 2021 Jan 28.
Listeria monocytogenes is an invasive foodborne pathogen that is ubiquitously present in the dairy farm environment. Although cattle are a reservoir of L. monocytogenes, most adult animals do not exhibit clinical symptoms, suggesting a homeostasis between this pathogen and the bovine gastrointestinal ecosystem. Nevertheless, substantial prevalence of L. monocytogenes fecal shedding by dairy cattle has been reported in many studies, posing threats of transmission within the herd and contamination of the human food supply. Accordingly, understanding the L. monocytogenes ecology within the bovine gastrointestinal tract is important to prevent clinical illness in the animal host, reduce transmission, and guide intervention strategies. In this study, we conducted a longitudinal sampling of fecal samples from 20 lactating dairy cows in one Wisconsin farm over a 29-d period and found a strikingly high incidence of L. monocytogenes shedding, in 90% of sampled animals. The L. monocytogenes isolates were genetically diverse, representing all common serotypes previously identified from cattle. Additionally, most tested isolates were resistant to ampicillin, and a few were also resistant to gentamicin or trimethoprim/sulfamethoxazole. Most isolates effectively infected human epithelial cells (Caco-2) and murine fibroblasts (L2), suggesting that they are all capable of causing systemic infection if the intestinal barrier is breached. Finally, we investigated the effects of L. monocytogenes colonization on the gastrointestinal tract microbiota by analyzing the fecal bacterial communities of some shedding and nonshedding cows. Whereas L. monocytogenes did not affect the α and β diversity of tested animals, a subset of shedding cows exhibited different abundances of certain operational taxonomic units within the Bacteroidetes and Firmicutes phyla compared with nonshedding cows. Overall, our findings highlight the threat of antibiotic resistance among some L. monocytogenes isolates, emphasize the need for a strain-specific approach in listeriosis treatment, and suggest the potential negative influence of subclinical L. monocytogenes carriage on animal gut health.
单核细胞增生李斯特菌是一种普遍存在于奶牛场环境中的侵袭性食源性病原体。尽管牛是李斯特菌的储存宿主，但大多数成年动物并不表现出临床症状，这表明该病原体与牛的胃肠道生态系统之间存在着一种平衡。然而，许多研究报告称，奶牛粪便中李斯特菌的大量排泄仍然存在，这对牛群内部的传播和人类食品供应的污染构成了威胁。因此，了解牛胃肠道内李斯特菌的生态对于预防动物宿主的临床疾病、减少传播和指导干预策略非常重要。在这项研究中，我们对威斯康星州一个奶牛场的 20 头哺乳期奶牛进行了为期 29 天的粪便样本纵向采样，发现 90%的采样动物都有明显的李斯特菌排泄现象。李斯特菌分离株具有遗传多样性，代表了以前从牛身上分离出的所有常见血清型。此外，大多数测试分离株对氨苄西林耐药，少数分离株对庆大霉素或复方新诺明耐药。大多数分离株能有效地感染人上皮细胞（Caco-2）和鼠成纤维细胞（L2），这表明如果肠道屏障被破坏，它们都有可能引起全身感染。最后，我们通过分析一些排泄和不排泄奶牛的粪便细菌群落，研究了李斯特菌定植对胃肠道微生物群的影响。虽然李斯特菌没有影响测试动物的α和β多样性，但与不排泄奶牛相比，一些排泄奶牛的厚壁菌门和Firmicutes 门内的某些操作分类单位的丰度存在差异。总的来说，我们的研究结果突出了一些李斯特菌分离株对抗生素耐药性的威胁，强调了在李斯特菌病治疗中需要采用特定菌株的方法，并提示了亚临床李斯特菌携带对动物肠道健康可能产生的负面影响。
