Persistence o Escherichia coli O157:H12 and Escherichia coli K12 as non-pathogenic surrogates for O157 on lettuce cultivars irrigated with alternative waters in the field

Authors: YIN, HSIN-BAI - University Of Maryland; GUPTA, NIDHI - University Of Maryland; CHEN, CHI-HUNG - University Of Maryland; PRADHAN, ABANI - University Of Maryland; Patel, Jitu; Boomer, Ashley

Submitted to: Frontiers in Sustainable Food Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2020
Publication Date: 11/24/2020
Citation: Yin, H., Gupta, N., Chen, C., Pradhan, A., Patel, J.R., Boomer, A.M. 2020. Persistence o Escherichia coli O157:H12 and Escherichia coli K12 as non-pathogenic surrogates for O157 on lettuce cultivars irrigated with alternative waters in the field. Frontiers in Sustainable Food Systems. https://doi.org/10.3389/fsufs.2020.555459.
DOI: https://doi.org/10.3389/fsufs.2020.555459

Interpretive Summary: Water scarcity has become an alarming issue due to increased food requirements for growing world population and other adverse environmental conditions. The use of non-traditional irrigation waters such as waste water and rain water can be used to overcome water scarcity. Further, farming certain cultivars of leafy greens which discourage enteric pathogen attachment on leaf surface will help in minimizing foodborne illnesses associated with consumption of leafy greens. We investigated the effect of treated wastewater (TW) and roof-collected rain water (RW) on the persistence of Escherichia coli surrogates on different lettuce cultivars (Annapolis, Celinet, and Coastline) on the field. The E. coli O157:H12 surrogate persisted at a significantly higher level than E. coli K12 on lettuce regardless of the water sources and lettuce cultivars. Lower number of bacteria were recovered from lettuce irrigated with TW than with RW immediately after irrigation. The difference in leaf characteristics of lettuce cultivars significantly influenced the persistence of these surrogates on lettuce leaves. Populations of E. coli O157:H12 recovered from RW-irrigated “Annapolis” lettuce were significantly lower than these bacteria recovered from “Celinet” and “Coastline” lettuce plants. Overall, survival of E. coli surrogates on lettuce was affected by the irrigation water sources and the plant cultivars. The research helps produce growers in selection of lettuce cultivars with lower bacterial attachment to minimize foodborne illnesses. It also helps growers to evaluate the risk assessments of TW and RW irrigation on lettuce in Mid-Atlantic area.

Technical Abstract: Treated wastewater (TW) and roof-collected rain water (RW) may serve as alternative irrigation water sources to decrease the pressure on the current water scarcity. The effect of TW and RW irrigation on the persistence of Escherichia coli surrogates on different lettuce cultivars grown at the farm was investigated. Field grown lettuce plants “Annapolis”, “Celinet”, and “Coastline” cultivars were spray-irrigated with groundwater (GW), TW, or RW containing 6 log CFU/ml of a mixture of antibiotic-resistant E. coli surrogates (E. coli O157:H12 and E. coli K12) in fecal slurry. On 0, 1, 3, 7 and 10 days-post-irrigation, four replicate lettuce samples (30 g/sample) from each group were collected and pummeled in 120 ml of buffered peptone water for 2 min, followed by plating on MacConkey agars with antibiotics. Results of the current study showed that E. coli O157:H12 persisted at a significantly higher level than E. coli K12 on lettuce regardless of the water sources and lettuce cultivars. TW irrigation resulted in the lowest bacterial recovery on the irrigated lettuce plants as compared to RW- and GW-irrigation on day 0. The difference in leaf characteristics of lettuce cultivars significantly? influenced the persistence of these surrogates on leaves. Populations of E. coli O157:H12 recovered from RW-irrigated “Annapolis” lettuce were significantly lower than these bacteria recovered from “Celinet” and “Coastline” lettuce plants (P<0.05). Overall, survival of E. coli surrogates on lettuce was affected by the irrigation water sources and the plant cultivars. Findings of this study can be used to evaluate the risk assessments of TW and RW irrigation on lettuce in Mid-Atlantic area.