Fate of 43 Salmonella Strains on Lettuce and Tomato Seedlings

Abstract

Multiple outbreaks of foodborne illness caused by Salmonella sp. have been linked to fresh produce. Understanding variability in colonization potential is critical for the selection of experimental strains suitable for research on the ecology of the species in growing food plants. The fate of 43 Salmonella strains from 29 serovars was examined on seedlings from two cultivars of lettuce (‘Winter Density’ and ‘Parris Island Cos’) and tomato (‘Amish Paste’ and ‘Manitoba’). Salmonella populations were measured on xylose lysine deoxycholate agar immediately after inoculation and after 5 days of incubation at 21°C. Laser scanning confocal microscopy was also performed to examine the distribution of cells on seedling leaf surfaces. Laser scanning confocal microscopy showed that cells or cellular aggregates were located within stomata, in surface depressions adjacent to stomata, or on random surface locations on seedlings that were successfully colonized. Populations of 26 strains (60.5%) increased on seedlings from all plant species and cultivars, although there were significant differences (P < 0.05) in the extent of population increase achieved by different strains on the same plant species–cultivar combinations. The remaining strains displayed differential ability to colonize seedlings depending on plant species or cultivar. The results of the present study indicate that the colonization potential of Salmonella is highly variable and should be carefully considered in the selection of experimental strains. HIGHLIGHTS

Inactivation of Salmonella enterica on post-harvest cantaloupe and lettuce by a lytic bacteriophage cocktail

“…The S. enterica strains selected for the experiments ( Table 2 ) were previously shown to colonize lettuce seedlings ( Wong et al., 2019 ). All were obtained from the Syst-OMICS Database (SALFOS, Université Laval, QC, Canada, https://salfos.ibis.ulaval.ca/ ).…”

A Simple Assay to Assess Salmonella enterica Persistence in Lettuce Leaves After Low Inoculation Dose

“…Although S. enterica induces plant defense responses ( Meng et al, 2013 ; Garcia and Hirt, 2014 ; Melotto et al, 2014 ; Oblessuc et al, 2020 ), it can still persist for long periods in the leaf apoplast depending on the bacterial strain and the plant genotype ( Wong et al, 2019 ; Jacob and Melotto, 2020 ). Furthermore, recent studies have shown that variations in the S. enterica culturing conditions, such as temperature and nutrients in the medium ( Kroupitski et al, 2019 ), and environmental conditions for the plant cultivation, such as temperature and humidity ( Deblais et al, 2019 ; Jechalke et al, 2019 ; Roy and Melotto, 2019 ), can interfere mainly with the ability of S. enterica to internalize plant tissues.…”

Human Pathogen Colonization of Lettuce Dependent Upon Plant Genotype and Defense Response Activation

“…In tomato, the level of S. enterica persistence in the phyllosphere after dip-inoculation with an eight-serovar cocktail (serovars Baildon, Cubana, Enteritidis, Havana, Mbandaka, Newport, Poona, and Schwarzengrund) also seems to be influenced by plant genotype (Barak et al, 2011). Furthermore, S. enterica seedling colonization of lettuce and tomato has been reported not only to be influenced by the plant species and cultivar, but also by the bacterial serovar and strain (Wong et al, 2019).…”