ARS | Publication request: Effect of spinach cultivar and strain variation on survival of Escherichia coli O157:H7 on spinach leaves

Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: March 6, 2012
Publication Date: July 25, 2012
Citation: Patel, J.R., Macarisin, D., Bauchan, G.R. 2012. Effect of spinach cultivar and strain variation on survival of Escherichia coli O157:H7 on spinach leaves. International Association for Food Protection. Paper No. T4-09.

Technical Abstract: Introduction: Escherichia coli O157:H7 outbreaks of infections associated with the consumption of fresh produce have increased in recent years. Bacterial cell surface appendages such as curli and the spinach leaf structure topography influence pathogen attachment and subsequent survival on spinach plant. 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 loom 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 (EDL933'csgA), cellulose (EDL933'bcsA), or both (EDL933'csgA/'bcsA). Four replicates of each plant shoot were analyzed for 14 days for E. coli O157: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.