Produce Safety and Microbiology Research Unit, United States Department of Agriculture, Agriculture Research Service, Western Regional Research Center, Albany, CA 94710, USA.
Pathogens. 2014 Jun 30;3(3):528-48. doi: 10.3390/pathogens3030528.
Airborne dust from feedlots is a potential mechanism of contamination of nearby vegetable crops with Escherichia coli O157:H7 (EcO157). We compared the fitness of clinical and environmental strains of EcO157 in <45 µm soil from a spinach farm. Differences in survival were observed among the 35 strains with D-values (days for 90% decreases) ranging from 1-12 days. Strains that survived longer, generally, were from environmental sources and lacked expression of curli, a protein associated with attachment and virulence. Furthermore, the proportion of curli-positive (C+) variants of EcO157 strains decreased with repeated soil exposure and the strains that were curli-negative (C-) remained C- post-soil exposure. Soil exposure altered expression of stress-response genes linked to fitness of EcO157, but significant clonal variation in expression was measured. Mutations were detected in the stress-related sigma factor, rpoS, with a greater percentage occurring in parental strains of clinical origin prior to soil exposure. We speculate that these mutations in rpoS may confer a differential expression of genes, associated with mechanisms of survival and/or virulence, and thus may influence the fitness of EcO157.
来自饲养场的空气传播尘埃是附近种植的蔬菜作物被大肠杆菌 O157:H7（EcO157）污染的潜在机制。我们比较了来自菠菜农场的 <45 µm 土壤中临床和环境 EcO157 菌株的适应性。在 35 株菌株中观察到存活差异，D 值（降低 90%所需的天数）范围为 1-12 天。通常，存活时间较长的菌株来自环境来源，且缺乏卷曲蛋白（一种与附着和毒力相关的蛋白）的表达。此外，EcO157 菌株中卷曲阳性（C+）变体的比例随着土壤暴露的重复而降低，而卷曲阴性（C-）的菌株在土壤暴露后仍保持 C-。土壤暴露改变了与 EcO157 适应性相关的应激反应基因的表达，但在表达水平上存在显著的克隆变异。应激相关 sigma 因子 rpoS 中检测到突变，在土壤暴露前，来自临床来源的亲本菌株中发生的突变百分比更高。我们推测，rpoS 中的这些突变可能赋予与生存和/或毒力相关的基因的差异表达，从而可能影响 EcO157 的适应性。
