Produce Safety and Microbiology Research Unit, U.S. Department of Agriculture, Agriculture Research Service, Western Regional Research Center, Albany, California, USA.
PLoS One. 2013;8(1):e54782. doi: 10.1371/journal.pone.0054782. Epub 2013 Jan 22.
Surviving predation is a fitness trait of Escherichia coli O157:H7 (EcO157) that provides ample time for the pathogen to be transported from reservoirs (e.g. dairies and feedlots) to farm produce grown in proximity. Ionophore dietary supplements that inhibit rumen protozoa may provide such a selective advantage for EcO157 to proliferate in lagoons as the pathogen is released along with the undigested supplement as manure washings. This study evaluated the fate of an outbreak strain of EcO157, protozoan and bacterial communities in wastewater treated with monensin. Although total protozoa and native bacteria were unaffected by monensin, the time for 90% decrease in EcO157 increased from 0.8 to 5.1 days. 18S and 16S rRNA gene sequencing of wastewater samples revealed that monensin eliminated almost all colpodean and oligohymenophorean ciliates, probably facilitating the extended survival of EcO157. Total protozoan numbers remained high in treated wastewater as monensin enriched 94% of protozoan sequences undetected with untreated wastewater. Monensin stimulated 30-fold increases in Cyrtohymena citrina, a spirotrichean ciliate, and also biflagellate bicosoecids and cercozoans. Sequences of gram-negative Proteobacteria increased from 1% to 46% with monensin, but gram-positive Firmicutes decreased from 93% to 46%. It is noteworthy that EcO157 numbers increased significantly (P<0.01) in Sonneborn medium containing monensin, probably due to monensin-inhibited growth of Vorticella microstoma (P<0.05), a ciliate isolated from wastewater. We conclude that dietary monensin inhibits ciliate protozoa that feed on EcO157. Feed supplements or other methods that enrich these protozoa in cattle manure could be a novel strategy to control the environmental dissemination of EcO157 from dairies to produce production environments.
抗捕食是大肠杆菌 O157:H7（EcO157）的一个适应特征，它为病原体从水库（如奶牛场和饲料场）传播到附近种植的农产品提供了充足的时间。抑制瘤胃原虫的离子载体饲料添加剂可能为 EcO157 在泻湖中大量繁殖提供了这样的选择性优势，因为病原体随着未消化的补充剂作为粪肥冲洗物一起释放。本研究评估了单诺菌素处理废水时爆发菌株 EcO157、原生动物和细菌群落的命运。尽管总原生动物和本地细菌不受单诺菌素影响，但 EcO157 减少 90%的时间从 0.8 天增加到 5.1 天。废水样品的 18S 和 16S rRNA 基因测序显示，单诺菌素几乎消除了所有的胶膜纤毛虫和寡膜纤毛虫，可能促进了 EcO157 的延长存活。由于单诺菌素富集了未经处理的废水中未检测到的 94%的原生动物序列，处理后的废水中总原生动物数量仍然很高。单诺菌素刺激了 Cyrtohymena citrina（一种旋口纤毛虫）以及双鞭毛的 bicosoecids 和 cercozoans 的 30 倍增长。革兰氏阴性变形菌的序列从 1%增加到 46%，而革兰氏阳性厚壁菌从 93%减少到 46%。值得注意的是，含有单诺菌素的 Sonneborn 培养基中 EcO157 的数量显著增加（P<0.01），这可能是由于单诺菌素抑制了从废水中分离出的喇叭虫（Vorticella microstoma）（P<0.05）的生长。我们得出的结论是，饮食中单诺菌素抑制了以 EcO157 为食的纤毛虫原生动物。在牛粪便中富集这些原生动物的饲料补充剂或其他方法可能是控制大肠杆菌 O157 从奶牛场向农产品生产环境传播的一种新策略。
