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Postharvest transfer and survival of Salmonella enterica serotype enteritidis on living lettuce

Waitt, J.A., Kuhn, D.D., Welbaum, G.E., Ponder, M.A.
Letters in applied microbiology 2014 v.58 no.2 pp. 95-101
Salmonella enterica, hands, humans, hydroponics, leaves, lettuce, markets, plastics, postharvest treatment, purchasing, risk, roots, serotypes, shelf life, storage temperature
The potential for postharvest transfer of Salmonella to ‘living lettuce’ is not well understood. In this study, the transfer of Salmonella enterica Enteritidis (6 log CFU g⁻¹) from worker hands or contaminated roots to leaves of living lettuce was quantified. Transfer rates of Salmonella from contaminated gloves to sequentially handled lettuce heads ranged from 94% to head 1, 82% to head 2 and 69% to head 3. On average, 2·9 ± 0·1 log CFU g⁻¹(64%) Salmonella was transferred from inoculated roots to leaves resulting from typical postharvest handling activities for living lettuce. Salmonella persisted on leaves stored at recommended storage temperatures (4°C) and increased 0·5 log CFU g⁻¹when stored at temperature abuse conditions (12°C). Salmonella increased 1·6 log CFU g⁻¹on roots after 18‐day storage at 12°C, emphasizing the need to maintain temperature control to reduce the risk of human illness. SIGNIFICANCE AND IMPACT OF THE STUDY: Hydroponically grown lettuce packaged in plastic clamshells with intact roots, marketed as ‘living lettuce’, is increasing in popularity due to its extended shelf life. This study demonstrates the transfer of Salmonella from contaminated worker hands and contaminated roots to leaves where it persisted at 4°C for 18 day. Temperature abuse (12°C) increased Salmonella on roots and leaves. These findings suggest that failure to maintain temperatures below 12°C can pose a risk for consumers purchasing living lettuce at markets where recommended storage temperatures are not maintained.