Purpose: Role of curli and cellulose in E. coli O157:H7 attachment and persistence to different spinach cultivars was evaluated.
Methods: Four organic spinach cultivars—Emilia, Lazio, Space, and Waitiki—were grown in sandy loam soil (3% organic matter). Leaves of four weeks old spinach plants were spot inoculated (100 µl in 5µl droplets, 5 log CFU/leaf) with E. coli O157:H7 strain EDL 933 and its isogenic mutants deficient in curli (EDL933DcsgA), cellulose (EDL933DbcsA), or both (EDL933DcsgA/DbcsA). Four replicates of each plant shoot were analyzed for 14 days for E. coliO157:H7 by spiral plating and MPN enrichment procedure. Leaf structure of spinach cultivars were observed under Low Temperature Scanning Electron (LT-SEM) and Variable Pressure Electron microscopy (VP-SEM).
Results: Curli expressing E. coli O157:H7 strains persisted at significantly higher level for 14 days on each spinach cultivar whereas curli deficient strains were undetectable after 7 days. Lack of cellulose expression did not affect its ability to persist on spinach leaves. The effect of spinach cultivar on E. coli O157:H7 persistence was not evident on days 0 and 1; however, significantly higher populations of E. coli O157:H7 were recovered from Waitiki cultivar during subsequent sampling on 7 and 14 days. Observation of the leave surface under LT-SEM did not found major differences in leaf structure among cultivars. However, quantitative topography analysis of the leave surface under VP-SEM revealed significantly greater surface roughness in Waitiki cultivar leaves.
Significance: Selection of spinach cultivars that restrict pathogen attachment to its surface can be useful intervention strategy in good agricultural practices to reduce potential produce-borne outbreaks.