Survival of Enteric Pathogens During Butterhead Lettuce Growth: Crop Stage, Leaf Age, and Irrigation

Abstract

The survival of Salmonella enterica serovar Thompson and Escherichia coli O157 was investigated on growing butterhead lettuce plants in the plant-growth chamber and greenhouse. All inoculation tests were made under conditions that approximate the greenhouse conditions for butterhead lettuce cultivation in Flanders (Belgium). The survival and proliferation of the pathogens on the leaves was determined at days 0, 4, and 8 after inoculation using standard plating techniques on selective medium. In the growth chamber, the extent to which both pathogens were able to multiply on the lettuce leaves was influenced by crop stage and leaf age. On young plants, the older leaves supported pathogen survival better. On nearly mature plants, pathogen population sizes were significantly higher on the old and young leaves compared with middle-aged leaves ( p < 0.001). In the greenhouse, the environmental regimen with high fluctuations in temperature and relative humidity was less conducive to the survival of E. coli O157, though its survival on nearly mature lettuce was enhanced by overhead irrigation. The moist conditions between the folded inner leaves are likely contributing to the survival of enteric pathogens in the lettuce head. Butterhead lettuce grown in greenhouses with a sprinkle irrigation system may present a potential health hazard when contaminated near harvest. Experimental design (growth chamber versus greenhouse) largely influences enteric pathogen behavior on growing lettuce plants.

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

“…As the initial inoculum level was higher than the maximum carrying capacity of the lettuce leaves, which is around 6 log CFU/g [61,62], the pathogen load on the leaves indeed declined. It has, however, already been shown that E. coli O157 is able to grow in the lettuce phyllosphere under high humidity conditions [61,63].…”

“…As the initial inoculum level was higher than the maximum carrying capacity of the lettuce leaves, which is around 6 log CFU/g [61,62], the pathogen load on the leaves indeed declined. It has, however, already been shown that E. coli O157 is able to grow in the lettuce phyllosphere under high humidity conditions [61,63]. Furthermore, we remark that the high inoculum density could also bias other aspects of E. coli O157 fitness in the phyllosphere, among which are the transition to a viable but non-culturable state [52] or changes in capacity to attach [64,65].…”

Scientific Opinion on the risk posed by pathogens in food of non‐animal origin. Part 2 (Salmonella and Norovirus in leafy greens eaten raw as salads)

“…However, (Brandl and Amundson, 2008), reported higher population of Salmonella enterica on young leaves than on middle leaves harvested from mature romaine lettuce heads, suggesting that leaf age may affect pre-harvest as well as on farm post-harvest colonization. The moist conditions between the folded inner leaves may contribute to the survival of enteric pathogens in the lettuce head (Van der Linden et al, 2013a).…”

“…They found that higher numbers of endogenous microorganisms on lettuce leaves reduced S. Enteritidis adhesion. Some experimental studies have reported that survival of Salmonella in lettuce during growing is relatively short (4-8 days) (Van der Linden et al, 2013a). However, it also has been reported that Salmonella persisted for up to 63 days and 231 days on lettuce and parsley, respectively (Islam et al, 2004b).…”

Fecal contamination in irrigation water and microbial quality of vegetable primary production in urban farms of Metro Manila, Philippines

“…[1][2][3][4][5] Particularly, irrigation water was implicated in several reported outbreaks linked to consumption of contaminated vegetables. One such case was related with an outbreak of Escherichia coli O157:H7 in Central Valley, California, from the consumption of contaminated lettuce and with a Salmonella Saintpaul outbreak in Mexico likely associated with contaminated Serrano peppers.…”