Transcriptional Responses of Escherichia coli K-12 and O157:H7 Associated with Lettuce Leaves

Abstract

An increasing number of outbreaks of gastroenteritis recently caused by Escherichia coli O157:H7 have been linked to the consumption of leafy green vegetables. Although it is known that E. coli survives and grows in the phyllosphere of lettuce plants, the molecular mechanisms by which this bacterium associates with plants are largely unknown. The goal of this study was to identify E. coli genes relevant to its interaction, survival, or attachment to lettuce leaf surfaces, comparing E. coli K-12, a model system, and E. coli O157:H7, a pathogen associated with a large number of outbreaks. Using microarrays, we found that upon interaction with intact leaves, 10.1% and 8.7% of the 3,798 shared genes were differentially expressed in K-12 and O157:H7, respectively, whereas 3.1% changed transcript levels in both. The largest group of genes downregulated consisted of those involved in energy metabolism, including tnaA (33-fold change), encoding a tryptophanase that converts tryptophan into indole. Genes involved in biofilm modulation (bhsA and ybiM) and curli production (csgA and csgB) were significantly upregulated in E. coli K-12 and O157:H7. Both csgA and bhsA (ycfR) mutants were impaired in the long-term colonization of the leaf surface, but only csgA mutants had diminished ability in short-term attachment experiments. Our data suggested that the interaction of E. coli K-12 and O157:H7 with undamaged lettuce leaves likely is initiated via attachment to the leaf surface using curli fibers, a downward shift in their metabolism, and the suppression of biofilm formation.

Microarray-Based Screening of Differentially Expressed Genes of E. coli O157:H7 Sakai during Preharvest Survival on Butterhead Lettuce

“…All the ribosomal subunit proteins were significantly repressed compared to their expression level 1 hpi (rpsUJT, rplCM at p < 0.05), as were other ribosomal subunit proteins (rpsFP at p < 0.01, rpsDIKT, rplKUXY at p < 0.05), and ftsN. This 2 dpi data agrees with the cell die-off after one day (see Figure 1) and with the data of Fink et al (2012) [4], who observed a decrease in the expression of the E. coli O157:H7 ribosomal-related genes 1 and 3 dpi onto detached lettuce leaves. Relative expression of E. coli O157:H7 Sakai ribosomal-related genes one hour and two days after inoculation on lettuce plants.…”

“…In parallel, the fate of the bacteria was determined with the conventional plate-counting technique. The results will be discussed and compared with the existing literature, in particular with two gene expression studies on lettuce and E. coli [3,4]. Since there are apparent similarities, a comparative overview between these and the current study has been compiled ( Table 1).…”

“…Escherichia coli O157:H7 (E. coli O157:H7) is one of the pathogens that is frequently involved and is of special interest due to the the culture was washed with sterile pretempered 10 mM MgSO 4 (230291, Sigma-Aldrich, S. Louis, MO, USA) at 18˝C (10 min, 5000ˆg, 4˝C), and re-suspended in sterile pretempered 10 mM MgSO 4 at 18˝C to an OD 600 of 0.5 which corresponded with 8.7˘0.1 log CFU/mL as determined by plate counting on the selective medium sorbitol MacConkey Agar (SMAC, Sigma-Aldrich, Sigma-Aldrich, St. Louis, MO, USA) (24 h, 37˝C). These MgSO 4 suspended cells were used as inoculum for the plants.…”

Transcriptomic Analysis of the Adaptation of Listeria monocytogenes to Growth on Vacuum-Packed Cold Smoked Salmon

“…A number of previous studies have analyzed the transcriptomes of foodborne pathogens under stress conditions commonly present on/in food matrices (including hyperosmotic stress, cold stress, hydrostatic pressure stress, antimicrobial stress, acid stress, and alkali stress), using laboratory media modified to simulate these conditions as a model (15)(16)(17)(18)(19)(20)(21)(22)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60)(61)(62)(63). These laboratory media include BHI broth (18,20,21,59), BHI agar (19), Luria-Bertani broth (60,61), tryptic soy broth (62), M9-glucose (63), and Listeria minimal medium (22) as reference conditions. The key differences between the reference condition that we used and CSS were that the CSS was vacuum packaged while the reference medium was not anaerobic (though MBHIB was incubated without shaking), L. monocytogenes was grown on the surface of CSS, while growth was planktonic in the liquid MBHIB, and CSS contains a number of unique components that cannot be easily added to BHIB at comparable concentrations (e.g., different phenolics, lipids, trace elements, etc.).…”

Genome-Based Comparison of Cyclic Di-GMP Signaling in Pathogenic and Commensal Escherichia coli Strains

“…Curli fibers are highly inflammatory (60,61) and, if expressed at 37°C, may therefore contribute to systemic absorption of Shiga toxin (30,62). Notably, curli fibers and cellulose also serve for attachment to surfaces of plants that are of importance for human nutrition and have repeatedly been implicated in EHEC transmission (63)(64)(65)(66).…”