Distinct Transcriptional Profiles and Phenotypes Exhibited by Escherichia coli O157:H7 Isolates Related to the 2006 Spinach-Associated Outbreak

Abstract

In 2006, a large outbreak of Escherichia coli O157:H7 was linked to the consumption of ready-to-eat bagged baby spinach in the United States. The likely sources of preharvest spinach contamination were soil and water that became contaminated via cattle or feral pigs in the proximity of the spinach fields. In this study, we compared the transcriptional profiles of 12 E. coli O157:H7 isolates that possess the same two-enzyme pulsed-field gel electrophoresis (PFGE) profile and are related temporally or geographically to the above outbreak. These E. coli O157:H7 isolates included three clinical isolates, five isolates from separate bags of spinach, and single isolates from pasture soil, river water, cow feces, and a feral pig. The three clinical isolates and two spinach bag isolates grown in cultures to stationary phase showed decreased expression of many S -regulated genes, including gadA, osmE, osmY, and katE, compared with the soil, water, cow, feral pig, and the other three spinach bag isolates. The decreased expression of these S -regulated genes was correlated with the decreased resistance of the isolates to acid stress, osmotic stress, and oxidative stress but increases in scavenging ability. We also observed that intraisolate variability was much more pronounced among the clinical and spinach isolates than among the environmental isolates. Together, the transcriptional and phenotypic differences of the spinach outbreak isolates of E. coli O157:H7 support the hypothesis that some variants within the spinach bag retained characteristics of the preharvest isolates, whereas other variants with altered gene expression and phenotypes infected the human host.

Investigation of Routes of Salmonella Contamination Via Soils and the Use of Mulch for Contamination Control during Lettuce Cultivation

“…For instance, outbreaks of Salmonella Typhimurium and Escherichia coli O157:H7 in Europe and USA were linked to leafy vegetables such as lettuce and spinach (Horby et al, 2003;Heaton and Jones, 2008;Parker et al, 2012). Epidemic survey also showed a high possibility of leafy vegetables infected with E. coli O157:H7 at the farm (Parker et al, 2012;Cooley et al, 2007).…”

“…Epidemic survey also showed a high possibility of leafy vegetables infected with E. coli O157:H7 at the farm (Parker et al, 2012;Cooley et al, 2007). In particular, Parker et al (2012) reported that a large outbreak of E. coli O157:H7 in 2006 was linked to the consumption of ready-to-eat baby spinach, likely contaminated by soil and water. From those reports, it is considered that the cultivation period is a critical point in preventing contamination with pathogenic bacteria.…”

Escherichia coli Survival in, and Release from, White-Tailed Deer Feces

“…However, in fragmented agricultural and forest landscapes, wildlife can contribute a large portion of the fecal pollution (8)(9)(10)(11), also serving as a reservoir for pathogens. E. coli O157:H7 was found in feral swine in Sweden (12) and in California, USA (13)(14)(15); E. coli O157:H7 were also isolated from feces of white-tailed deer cograzing with cattle (16)(17)(18). Black-tailed deer were identified as a source of E. coli O157:H7 strawberry-transmitted infection in Oregon, which caused 15 illness cases, including two deaths (19).…”

RcsB Contributes to the Distinct Stress Fitness among Escherichia coli O157:H7 Curli Variants of the 1993 Hamburger-Associated Outbreak Strains

“…RNA extraction, cDNA labeling, and microarray hybridization were performed as described previously with slight modifications (37,50). Briefly, total RNA was extracted using the Promega SV total RNA kit, with additions of 3 mg ml Ϫ1 of lysozyme (Fisherbrand) to a bacterial cell suspension.…”