Survival of Salmonella enterica and Escherichia coli O157:H7 Sprayed onto the Foliage of Field-Grown Cabbage Plants

Abstract

To reduce the number of cabbage pathogen outbreaks, it is essential to understand the fate of enteric pathogens that contaminate plants in the field. To assist in that effort, two independent trials were conducted with a red cultivar (cv. Red Dynasty) and a green cultivar (cv. Bravo F1) of field-grown cabbage (Brassica oleracea var. capitata). In the first trial, plants with small heads were sprayed with an inoculum containing both attenuated Salmonella enterica Typhimurium and Escherichia coli O157:H7 (5.0 log CFU/mL). Initial pathogen levels (ca. 3.9 log CFU per head), determined through plate count enumeration (limit of detection was 1.3 log CFU/g), dropped precipitously such that 2 days later, they could not be detected by enrichment culture in 22 to 35% of the heads. However, subsequent declines were at a slower rate; no differences were observed between red and green cabbage heads (P > 0.05), and heads were still positive for the pathogens 22 days after being sprayed with the inoculum. As a result, the logistic model revealed that for every 2 days contaminated cabbage heads remained in the field, the probability of finding a positive sample decreased by a factor of 1.1 (95% confidence interval from 1.0 to 1.2, P = 0.0022) and 1.2 (95% confidence interval from 1.0 to 1.4, P ≤ 0.0001) for Salmonella and E. coli O157:H7, respectively. In the second trial occurring 2 weeks later, plants with medium red or green cabbage heads were sprayed with an inoculum at a dose of 3.5 log CFU/mL. A similar decay in prevalence over time occurred for green cabbage as in trial 1; however, pathogen decline in red cabbage was less in trial 2 than in trial 1. The extended persistence of pathogens in cabbage heads exhibited in both trials infers that harvest of contaminated cabbage destined for raw consumption is risky. Additional field studies are necessary to determine whether similar pathogen fates occur in other regions or climates and to clarify the effect of the maturity of red cabbage on pathogen inactivation.

Survival of Escherichia coli and Listeria innocua on Lettuce after Irrigation with Contaminated Water in a Temperate Climate

“…L. monocytogenes has been reported to survive in green herbs produced in a glasshouse environment for up to 28 days after inoculation via overhead spray irrigation [ 40 ]. Extended survival periods of different strains of E. coli and Listeria have been demonstrated for other production conditions, such as trials conducted in growth chambers [ 33 , 35 ] or field production conditions [ 37 , 38 , 41 , 42 , 61 ].…”

“…Moreover, due to the morphological characteristics of lettuce plants, there is the potential for retention of irrigation water when delivered via overhead spray. This will facilitate the accumulation of water and potentially pathogenic bacteria in the inner parts of the plant, favouring bacterial survival [ 32 , 61 ]. Another possible scenario that could explain the observed die-off dynamics could be a potential heterogeneity within the inoculated bacteria (specifically heterogeneous bacterial populations in stationary phase) and/or the adaptation of the surviving fraction of the initial inoculum to the plant environment [ 63 ].…”

Frontiers in Plant Breeding: Perspectives for the Selection of Vegetables Less Susceptible to Enteric Pathogens

“…The study showed that surface survival of both Salmonella and Escherichia coli O157:H7 on small cabbage plants over nine days was significantly affected by cultivars: pathogens survived the most on the cultivar "Farao" (Erickson et al, 2019b). In a field study which compared medium-sized cabbage heads, 'Red Dinasty' was more likely to be positive for Salmonella and E. coli O157:H7 (3.0 and 11.5 times, respectively) on day 5 post-inoculation when compared with the cultivar 'Bravo F1' (Erickson et al, 2019a).…”

“…Response of cabbage cultivars to internalization or surface survival of Salmonella and Escherichia coli O157:H7 was studied by Erickson et al (2019a;2019b). In a growth chamber study, internalized Salmonella was detected in cabbage within 24 h with prevalence ranging from 62% plants for the cultivar 'Super Red 80' to 92% for 'Red Dynasty.'…”