Ravva Subbarao V, Sarreal Chester Z, Mandrell Robert E
Produce Safety and Microbiology Research Unit, U.S. Department of Agriculture, Agriculture Research Service, Western Regional Research Center, Albany, California, United States of America.
PLoS One. 2014 Jul 14;9(7):e102412. doi: 10.1371/journal.pone.0102412. eCollection 2014.
Escherichia coli O157:H7 (EcO157) associated with the 2006 spinach outbreak appears to have persisted as the organism was isolated, three months after the outbreak, from environmental samples in the produce production areas of the central coast of California. Survival in harsh environments may be linked to the inherent fitness characteristics of EcO157. This study evaluated the comparative fitness of outbreak-related clinical and environmental strains to resist protozoan predation and survive in soil from a spinach field in the general vicinity of isolation of strains genetically indistinguishable from the 2006 outbreak strains. Environmental strains from soil and feral pig feces survived longer (11 to 35 days for 90% decreases, D-value) with Vorticella microstoma and Colpoda aspera, isolated previously from dairy wastewater; these D-values correlated (P<0.05) negatively with protozoan growth. Similarly, strains from cow feces, feral pig feces, and bagged spinach survived significantly longer in soil compared to clinical isolates indistinguishable by 11-loci multi-locus variable-number tandem-repeat analysis. The curli-positive (C+) phenotype, a fitness trait linked with attachment in ruminant and human gut, decreased after exposure to protozoa, and in soils only C- cells remained after 7 days. The C+ phenotype correlated negatively with D-values of EcO157 exposed to soil (rs = -0.683; P = 0.036), Vorticella (rs = -0.465; P = 0.05) or Colpoda (rs = -0.750; P = 0.0001). In contrast, protozoan growth correlated positively with C+ phenotype (Vorticella, rs = 0.730, P = 0.0004; Colpoda, rs = 0.625, P = 0.006) suggesting a preference for consumption of C+ cells, although they grew on C- strains also. We speculate that the C- phenotype is a selective trait for survival and possibly transport of the pathogen in soil and water environments.
与2006年菠菜疫情相关的大肠杆菌O157:H7（EcO157）似乎一直存在，因为在疫情爆发三个月后，从加利福尼亚州中部海岸农产品生产区的环境样本中分离出了这种微生物。在恶劣环境中的存活可能与EcO157的固有适应性特征有关。本研究评估了与疫情相关的临床菌株和环境菌株在抵抗原生动物捕食以及在与2006年疫情菌株基因无法区分的菌株分离地附近的菠菜田土壤中存活的相对适应性。从土壤和野猪粪便中分离出的环境菌株在与先前从乳品废水中分离出的小口钟虫和粗颈肾形虫共同培养时存活时间更长（90%数量减少时的D值为11至35天）；这些D值与原生动物生长呈负相关（P<0.05）。同样，通过11个位点的多位点可变数目串联重复分析无法区分的情况下，来自牛粪、野猪粪便和袋装菠菜的菌株在土壤中的存活时间明显长于临床分离株。卷曲蛋白阳性（C+）表型是一种与在反刍动物和人类肠道中附着有关的适应性特征，在接触原生动物后会减少，并且在土壤中7天后仅剩下C-细胞。C+表型与暴露于土壤（rs = -0.683；P = 0.036）、钟虫（rs = -0.465；P = 0.05）或肾形虫（rs = -0.750；P = 0.0001）的EcO157的D值呈负相关。相反，原生动物生长与C+表型呈正相关（钟虫，rs = 0.730，P = 0.0004；肾形虫，rs = 0.625，P = 0.006），这表明原生动物更倾向于消耗C+细胞，尽管它们也能在C-菌株上生长。我们推测C-表型是病原体在土壤和水环境中存活以及可能传播的一个选择性特征。
