Fate of Salmonella enterica and Enterohemorrhagic Escherichia coli Cells Artificially Internalized into Vegetable Seeds during Germination

ABSTRACTVegetable seeds contaminated with bacterial pathogens have been linked to fresh-produce-associated outbreaks of gastrointestinal infections. This study was undertaken to observe the physiological behavior ofSalmonella entericaand enterohemorrhagicEscherichia coli(EHEC) cells artificially internalized into vegetable seeds during the germination process. Surface-decontaminated seeds of alfalfa, fenugreek, lettuce, and tomato were vacuum-infiltrated with four individual strains ofSalmonellaor EHEC. Contaminated seeds were germinated at 25°C for 9 days, and different sprout/seedling tissues were microbiologically analyzed every other day. The internalization ofSalmonellaand EHEC cells into vegetable seeds was confirmed by the absence of pathogens in seed-rinsing water and the presence of pathogens in seed homogenates after postinternalization seed surface decontamination. Results show that 317 (62%) and 343 (67%) of the 512 collected sprout/seedling tissue samples were positive forSalmonellaand EHEC, respectively. The averageSalmonellapopulations were significantly larger (P< 0.05) than the EHEC populations. Significantly largerSalmonellapopulations were recovered from the cotyledon and seed coat tissues, followed by the root tissues, but the mean EHEC populations from all sampled tissue sections were statistically similar, except in pregerminated seeds. ThreeSalmonellaand two EHEC strains had significantly larger cell populations on sprout/seedling tissues than other strains used in the study.Salmonellaand EHEC populations from fenugreek and alfalfa tissues were significantly larger than those from tomato and lettuce tissues. The study showed the fate of internalized human pathogens on germinating vegetable seeds and sprout/seedling tissues and emphasized the importance of using pathogen-free seeds for sprout production.IMPORTANCEThe internalization of microorganisms into vegetable seeds could occur naturally and represents a possible pathway of vegetable seed contamination by human pathogens. The present study investigated the ability of two important bacterial pathogens,Salmonellaand enterohemorrhagicEscherichia coli(EHEC), when artificially internalized into vegetable seeds, to grow and disseminate along vegetable sprouts/seedlings during germination. The data from the study revealed that the pathogen cells artificially internalized into vegetable seeds caused the contamination of different tissues of sprouts/seedlings and that pathogen growth on germinating seeds is bacterial species and vegetable seed-type dependent. These results further stress the necessity of using pathogen-free vegetable seeds for edible sprout production.

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Influence of Bacterial Competitors on Salmonella enterica and Enterohemorrhagic Escherichia coli Growth in Microbiological Media and Attachment to Vegetable Seeds

Foods ◽

10.3390/foods10020285 ◽

2021 ◽

Vol 10 (2) ◽

pp. 285

Author(s):

Da Liu ◽

Ronald Walcott ◽

Kevin Mis Solval ◽

Jinru Chen

Keyword(s):

Escherichia Coli ◽

Foodborne Pathogens ◽

Salmonella Enterica ◽

Lactobacillus Rhamnosus ◽

Probiotic Bacterium ◽

Enterohemorrhagic Escherichia Coli ◽

Biocontrol Agents ◽

Human Pathogens ◽

Bacterial Strains ◽

Pathogen Populations

Interests in using biological agents for control of human pathogens on vegetable seeds are rising. This study evaluated whether probiotic bacterium Lactobacillus rhamnosus GG, bacterial strains previously used as biocontrol agents in plant science, as well as a selected plant pathogen could compete with foodborne human pathogens, such as Salmonella enterica and enterohemorrhagic Escherichia coli (EHEC), for growth in microbiological media and attachment to vegetable seeds; and to determine whether the metabolites in cell-free supernatants of competitive bacterial spent cultures could inhibit the growth of the two pathogens. The results suggest that the co-presence of competitive bacteria, especially L. rhamnosus GG, significantly (p < 0.05) inhibited the growth of Salmonella and EHEC. Cell-free supernatants of L. rhamnosus GG cultures significantly reduced the pathogen populations in microbiological media. Although not as effective as L. rhamnosus GG in inhibiting the growth of Salmonella and EHEC, the biocontrol agents were more effective in competing for attachment to vegetable seeds. The study observed the inhibition of human bacterial pathogens by competitive bacteria or their metabolites and the competitive attachment to sprout seeds among all bacteria involved. The results will help strategize interventions to produce vegetable seeds and seed sprouts free of foodborne pathogens.

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Colonization of Arabidopsis thaliana with Salmonella enterica and Enterohemorrhagic Escherichia coli O157:H7 and Competition by Enterobacter asburiae

Applied and Environmental Microbiology ◽

10.1128/aem.69.8.4915-4926.2003 ◽

2003 ◽

Vol 69 (8) ◽

pp. 4915-4926 ◽

Cited By ~ 205

Author(s):

Michael B. Cooley ◽

William G. Miller ◽

Robert E. Mandrell

Keyword(s):

Escherichia Coli ◽

Arabidopsis Thaliana ◽

Salmonella Enterica ◽

Fluorescent Protein ◽

Enterohemorrhagic Escherichia Coli ◽

Plant Responses ◽

Human Pathogens ◽

E Coli ◽

Green Fluorescent ◽

Enterobacter Asburiae

ABSTRACT Enteric pathogens, such as Salmonella enterica and Escherichia coli O157:H7, have been shown to contaminate fresh produce. Under appropriate conditions, these bacteria will grow on and invade the plant tissue. We have developed Arabidopsis thaliana (thale cress) as a model system with the intention of studying plant responses to human pathogens. Under sterile conditions and at 100% humidity, S. enterica serovar Newport and E. coli O157:H7 grew to 109 CFU g−1 on A. thaliana roots and to 2 × 107 CFU g−1 on shoots. Furthermore, root inoculation led to contamination of the entire plant, indicating that the pathogens are capable of moving on or within the plant in the absence of competition. Inoculation with green fluorescent protein-labeled S. enterica and E. coli O157:H7 showed invasion of the roots at lateral root junctions. Movement was eliminated and invasion decreased when nonmotile mutants of S. enterica were used. Survival of S. enterica serovar Newport and E. coli O157:H7 on soil-grown plants declined as the plants matured, but both pathogens were detectable for at least 21 days. Survival of the pathogen was reduced in unautoclaved soil and amended soil, suggesting competition from indigenous epiphytes from the soil. Enterobacter asburiae was isolated from soil-grown A. thaliana and shown to be effective at suppressing epiphytic growth of both pathogens under gnotobiotic conditions. Seed and chaff harvested from contaminated plants were occasionally contaminated. The rate of recovery of S. enterica and E. coli O157:H7 from seed varied from undetectable to 19% of the seed pools tested, depending on the method of inoculation. Seed contamination by these pathogens was undetectable in the presence of the competitor, Enterobacter asburiae. Sampling of 74 pools of chaff indicated a strong correlation between contamination of the chaff and seed (P = 0.025). This suggested that contamination of the seed occurred directly from contaminated chaff or by invasion of the flower or silique. However, contaminated seeds were not sanitized by extensive washing and chlorine treatment, indicating that some of the bacteria reside in a protected niche on the seed surface or under the seed coat.

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Evaluation of Aerated Steam Treatment of Alfalfa and Mung Bean Seeds To Eliminate High Levels of Escherichia coli O157:H7 and O178:H12, Salmonella enterica, and Listeria monocytogenes

Applied and Environmental Microbiology ◽

10.1128/aem.00443-13 ◽

2013 ◽

Vol 79 (15) ◽

pp. 4613-4619 ◽

Cited By ~ 14

Author(s):

Patrick Studer ◽

Werner E. Heller ◽

Jörg Hummerjohann ◽

David Drissner

Keyword(s):

Escherichia Coli ◽

Listeria Monocytogenes ◽

Salmonella Enterica ◽

Mung Bean ◽

Germination Rate ◽

Steam Treatment ◽

Heat Sensitivity ◽

Human Pathogens ◽

Content Type ◽

E Coli

ABSTRACTSprouts contaminated with human pathogens are able to cause food-borne diseases due to the favorable growth conditions for bacteria during germination and because of minimal processing steps prior to consumption. We have investigated the potential of hot humid air, i.e., aerated steam, to treat alfalfa and mung bean seeds which have been artificially contaminated withEscherichia coliO157:H7,Salmonella entericasubsp.entericaserovar Weltevreden, andListeria monocytogenesScott A. In addition, a recently collectedE. coliO178:H12 isolate, characterized by a reduced heat sensitivity, was exposed to the treatment described. Populations ofE. coliO157:H7 andS. entericaon alfalfa and mung bean seeds could be completely eliminated by a 300-s treatment with steam at 70 ± 1°C as revealed by enrichment studies.L. monocytogenesandE. coliO178:H12 could not be completely eliminated from artificially inoculated seeds. However, bacterial populations were reduced by more than 5 log CFU/g on alfalfa and by more than 4 log CFU/g on mung bean seeds. The germination rate of mung beans was not affected by the 300-s treatment compared to the germination rate of untreated seeds whereas that of alfalfa seeds was significantly lower by 11.9%. This chemical-free method is an effective alternative to the 20,000-ppm hypochlorite treatment presently recommended by the U.S. Food and Drug Administration (FDA).

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Surfing Motility: a Conserved yet Diverse Adaptation among Motile Bacteria

Journal of Bacteriology ◽

10.1128/jb.00394-18 ◽

2018 ◽

Vol 200 (23) ◽

Cited By ~ 6

Author(s):

Evelyn Sun ◽

Sijie Liu ◽

Robert E. W. Hancock

Keyword(s):

Escherichia Coli ◽

Pseudomonas Aeruginosa ◽

Quorum Sensing ◽

Broad Spectrum ◽

Proteus Mirabilis ◽

Salmonella Enterica ◽

Bacterial Species ◽

Content Type ◽

Adaptive Resistance ◽

Sensing Systems

ABSTRACTBacterial rapid surfing motility is a novel surface adaptation ofPseudomonas aeruginosain the presence of the glycoprotein mucin. Here, we show that other Gram-negative motile bacterial species, includingEscherichia coli,Salmonella enterica,Vibrio harveyi,Enterobacter cloacae, andProteus mirabilis, also exhibit the physical characteristics of surfing on the surface of agar plates containing 0.4% mucin, where surfing motility was generally more rapid and less dependent on medium viscosity than was swimming motility. As previously observed inPseudomonas aeruginosa, all surfing species exhibited some level of broad-spectrum adaptive resistance, although the antibiotics to which they demonstrated surfing-mediated resistance differed. Surfing motility inP. aeruginosawas found to be dependent on the quorum-sensing systems of this organism; however, this aspect was not conserved in other tested bacterial species, includingV. harveyiandS. enterica, as demonstrated by assaying specific quorum-sensing mutants. Thus, rapid surfing motility is a complex surface growth adaptation that is conserved in several motile bacteria, involves flagella, and leads to diverse broad-spectrum antibiotic resistance, but it is distinct in terms of dependence on quorum sensing.IMPORTANCEThis study showed for the first time that surfing motility, a novel form of surface motility first discovered inPseudomonas aeruginosaunder artificial cystic fibrosis conditions, including the presence of high mucin content, is conserved in other motile bacterial species known to be mucosa-associated, includingEscherichia coli,Salmonella enterica, andProteus mirabilis. Here, we demonstrated that key characteristics of surfing, including the ability to adapt to various viscous environments and multidrug adaptive resistance, are also conserved. Using mutagenesis assays, we also identified the importance of all three known quorum-sensing systems, Las, Rhl, and Pqs, inP. aeruginosain regulating surfing motility, and we also observed a conserved dependence of surfing on flagella in certain species.

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Retinoid Levels Influence Enterohemorrhagic Escherichia coli Infection and Shiga Toxin 2 Susceptibility in Mice

Infection and Immunity ◽

10.1128/iai.02191-14 ◽

2014 ◽

Vol 82 (9) ◽

pp. 3948-3957 ◽

Cited By ~ 6

Author(s):

Gabriel Cabrera ◽

Romina J. Fernández-Brando ◽

María Jimena Abrey-Recalde ◽

Ariela Baschkier ◽

Alipio Pinto ◽

...

Keyword(s):

Escherichia Coli ◽

Shiga Toxin ◽

Lethal Dose ◽

Absolute Number ◽

Enterohemorrhagic Escherichia Coli ◽

Polymorphonuclear Cells ◽

Intestinal Damage ◽

Gastrointestinal Infections ◽

Systemic Complications ◽

Content Type

ABSTRACTEnterohemorrhagicEscherichia coli(EHEC) is a food-borne pathogen that produces Shiga toxin (Stx) and causes hemorrhagic colitis. Under some circumstances, Stx produced within the intestinal tract enters the bloodstream, leading to systemic complications that may cause the potentially fatal hemolytic-uremic syndrome. Although retinoids like vitamin A (VA) and retinoic acid (RA) are beneficial to gut integrity and the immune system, the effect of VA supplementation on gastrointestinal infections of different etiologies has been controversial. Thus, the aim of this work was to study the influence of different VA status on the outcome of an EHEC intestinal infection in mice. We report that VA deficiency worsened the intestinal damage during EHEC infection but simultaneously improved survival. Since death is associated mainly with Stx toxicity, Stx was intravenously inoculated to analyze whether retinoid levels affect Stx susceptibility. Interestingly, while VA-deficient (VA-D) mice were resistant to a lethal dose of Stx2, RA-supplemented mice were more susceptible to it. Given that peripheral blood polymorphonuclear cells (PMNs) are known to potentiate Stx2 toxicity, we studied the influence of retinoid levels on the absolute number and function of PMNs. We found that VA-D mice had decreased PMN numbers and a diminished capacity to produce reactive oxygen species, while RA supplementation had the opposite effect. These results are in line with the well-known function of retinoids in maintaining the homeostasis of the gut but support the idea that they have a proinflammatory effect by acting, in part, on the PMN population.

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Impact of Acanthamoeba Cysts on Stress Resistance of Salmonella enterica Serovar Typhimurium, Yersinia enterocolitica 4/O:3, Listeria monocytogenes 1/2a, and Escherichia coli O:26

Applied and Environmental Microbiology ◽

10.1128/aem.00754-17 ◽

2017 ◽

Vol 83 (14) ◽

Cited By ~ 6

Author(s):

Ellen Lambrecht ◽

Julie Baré ◽

Koen Sabbe ◽

Kurt Houf

Keyword(s):

Escherichia Coli ◽

Listeria Monocytogenes ◽

Yersinia Enterocolitica ◽

Sodium Hypochlorite ◽

Salmonella Enterica ◽

Bacterial Pathogens ◽

Cross Tolerance ◽

Free Living ◽

Content Type ◽

Physical And Chemical

ABSTRACT The formation of robust resting cysts enables Acanthamoeba to resist harsh environmental conditions. This study investigated to what extent these cysts are resistant to physical and chemical stresses as applied in food industry cleaning and disinfection procedures. Moreover, it was assessed whether certain intracystic meat-borne bacterial pathogens are more stress resistant than free-living bacterial monocultures and if intracystic passage and subsequent association with trophozoites induces cross-tolerance toward other stressors. Several physical and chemical stressors (NaCl, H2O2, benzalkonium chloride, 55°C, heating until boiling, ethanol, dishwashing detergent, and sodium hypochlorite) frequently used in domestic and industrial food-related environments were tested against (i) Acanthamoeba castellanii cysts, (ii) single strains of bacterial monocultures, (iii) intracystic bacteria, and (iv) bacteria after intracystic passage (cyst-primed bacteria). Only heating until boiling and hypochlorite treatment were cysticidal. After boiling, no viable trophozoites could be recovered from the cysts, and hypochlorite treatment caused a 1.34- to 4.72-log10 cells/ml reduction in cyst viability. All treatments were effective in reducing or even eliminating the tested bacterial monocultures, whereas bacteria residing inside cysts were more tolerant toward these stressors. All cyst-primed bacteria exhibited an increased tolerance toward subsequent H2O2 (>92% decrease in median log10 CFU/ml reduction) and 70% ethanol (>99% decrease) treatments. Moreover, intracystic passage significantly increased the survival of Yersinia enterocolitica (74% decrease in median log10 reduction), Escherichia coli (58%), and Salmonella enterica (48%) after NaCl treatment and of E. coli (96%), S. enterica (99%), and Listeria monocytogenes (99%) after sodium hypochlorite treatment compared with that of nonprimed bacteria. IMPORTANCE The results from this study demonstrated that both viable and nonviable amoebal cysts can protect internalized bacteria against stressful conditions. Moreover, cyst passage can induce cross-tolerance in bacteria, increasing their survival when exposed to selected stressors. These findings underscore the potential importance of free-living amoebae in food-related environments and their impact on the persistence of meat-borne bacterial pathogens.

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Dissemination of IncI2 Plasmids That Harbor theblaCTX-MElement among Clinical Salmonella Isolates

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.00775-15 ◽

2015 ◽

Vol 59 (8) ◽

pp. 5026-5028 ◽

Cited By ~ 20

Author(s):

Marcus Ho-yin Wong ◽

Lizhang Liu ◽

Meiying Yan ◽

Edward Wai-chi Chan ◽

Sheng Chen

Keyword(s):

Escherichia Coli ◽

Salmonella Enterica ◽

Bacterial Pathogens ◽

Content Type ◽

E Coli ◽

Species Migration ◽

Typhimurium Strain ◽

Extended Spectrum ◽

Multiple Antibiotics

ABSTRACTThe extended-spectrum-β-lactamase (ESBL) determinant CTX-M-55 is increasingly prevalent inEscherichia colibut remains extremely rare inSalmonella. This study reports the isolation of a plasmid harboring theblaCTX-M-55element in a clinicalSalmonella entericaserotype Typhimurium strain resistant to multiple antibiotics. This plasmid is genetically identical to several known IncI2-type elements harbored byE. colistrains recovered from animals. This finding indicates that IncI2 plasmids harboring theblaCTX-Mgenes may undergo cross-species migration among potential bacterial pathogens, withE. colias the major source of such elements.

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Differential Attachment of Salmonella enterica and Enterohemorrhagic Escherichia coli to Alfalfa, Fenugreek, Lettuce, and Tomato Seeds

Applied and Environmental Microbiology ◽

10.1128/aem.03170-16 ◽

2017 ◽

Vol 83 (7) ◽

Cited By ~ 9

Author(s):

Yue Cui ◽

Ronald Walcott ◽

Jinru Chen

Keyword(s):

Escherichia Coli ◽

Bacterial Pathogens ◽

Surface Characteristics ◽

Enterohemorrhagic Escherichia Coli ◽

Unit Weight ◽

Plate Count ◽

Fenugreek Seeds ◽

Content Type ◽

Fungicide Treatment ◽

Tomato Seeds

ABSTRACT Vegetable seeds have the potential to disseminate and transmit foodborne bacterial pathogens. This study was undertaken to assess the abilities of selected Salmonella and enterohemorrhagic Escherichia coli (EHEC) strains to attach to fungicide-treated versus untreated, and intact versus mechanically damaged, seeds of alfalfa, fenugreek, lettuce, and tomato. Surface-sanitized seeds (2 g) were exposed to four individual strains of Salmonella or EHEC at 20°C for 5 h. Contaminated seeds were rinsed twice, each with 10 ml of sterilized water, before being soaked overnight in 5 ml of phosphate-buffered saline at 4°C. The seeds were then vortexed vigorously for 1 min, and pathogen populations in seed rinse water and soaking buffer were determined using a standard plate count assay. In general, the Salmonella cells had higher attachment ratios than the EHEC cells. Lettuce seeds by unit weight had the highest numbers of attached Salmonella or EHEC cells, followed by tomato, alfalfa, and fenugreek seeds. In contrast, individual fenugreek seeds had more attached pathogen cells, followed by lettuce, alfalfa, and tomato seeds. Significantly more Salmonella and EHEC cells attached to mechanically damaged seeds than to intact seeds (P < 0.05). Although, on average, significantly more Salmonella and EHEC cells were recovered from untreated than fungicide-treated seeds (P < 0.05), fungicide treatment did not significantly affect the attachment of individual bacterial strains to vegetable seeds (P > 0.05), with a few exceptions. This study fills gaps in the current body of literature and helps explain bacterial interactions with vegetable seeds with differing surface characteristics. IMPORTANCE Vegetable seeds, specifically sprout seeds, have the potential to disseminate and transmit foodborne bacterial pathogens. This study investigated the interaction between two important bacterial pathogens, i.e., Salmonella and EHEC, and vegetable seeds with differing surface characteristics. This research helps understand whether seed surface structure, integrity, and fungicide treatment affect the interaction between bacterial cells and vegetable seeds.

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Salmonella enterica Suppresses Pectobacterium carotovorum subsp. carotovorum Population and Soft Rot Progression by Acidifying the Microaerophilic Environment

mBio ◽

10.1128/mbio.00557-12 ◽

2013 ◽

Vol 4 (1) ◽

Cited By ~ 24

Author(s):

Grace Kwan ◽

Amy O. Charkowski ◽

Jeri D. Barak

Keyword(s):

Escherichia Coli ◽

Disease Progression ◽

Salmonella Enterica ◽

Soft Rot ◽

Pectobacterium Carotovorum ◽

Human Pathogens ◽

Bacterial Populations ◽

Content Type ◽

E Coli ◽

The Impact

ABSTRACTAlthough enteric human pathogens are usually studied in the context of their animal hosts, a significant portion of their life cycle occurs on plants. Plant disease alters the phyllosphere, leading to enhanced growth of human pathogens; however, the impact of human pathogens on phytopathogen biology and plant health is largely unknown. To characterize the interaction between human pathogens and phytobacterial pathogens in the phyllosphere, we examined the interactions betweenPectobacterium carotovorumsubsp.carotovorumandSalmonella entericaorEscherichia coliO157:H7 with regard to bacterial populations, soft rot progression, and changes in local pH. The presence ofP. carotovorumsubsp.carotovorumenhanced the growth of bothS. entericaandE. coliO157:H7 on leaves. However, in a microaerophilic environment,S. entericareducedP. carotovorumsubsp.carotovorumpopulations and soft rot progression by moderating local environmental pH. Reduced soft rot was not due toS. entericaproteolytic activity. Limitations onP. carotovorumsubsp.carotovorumgrowth, disease progression, and pH elevation were not observed on leaves coinoculated withE. coliO157:H7 or when leaves were coinoculated withS. entericain an aerobic environment.S. entericaalso severely undermined the relationship between the phytobacterial population and disease progression of aP. carotovorumsubsp.carotovorum budBmutant defective in the 2,3-butanediol pathway for acid neutralization. Our results show thatS. entericaandE. coliO157:H7 interact differently with the enteric phytobacterial pathogenP. carotovorumsubsp.carotovorum.S. entericainhibition of soft rot progression may conceal a rapidly growing human pathogen population. Whereas soft rotted produce can alert consumers to the possibility of food-borne pathogens, healthy-looking produce may entice consumption of contaminated vegetables.IMPORTANCESalmonella entericaandEscherichia coliO157:H7 may use plants to move between animal and human hosts. Their populations are higher on plants cocolonized with the common bacterial soft rot pathogenPectobacterium carotovorumsubsp.carotovorum, turning edible plants into a risk factor for human disease. We inoculated leaves withP. carotovorumsubsp.carotovorumandS. entericaorE. coliO157:H7 to study the interactions between these bacteria. WhileP. carotovorumsubsp.carotovorumenhanced the growth of bothS. entericaandE. coliO157:H7, these human pathogens affectedP. carotovorumsubsp.carotovorumfundamentally differently.S. entericareducedP. carotovorumsubsp.carotovorumgrowth and acidified the environment, leading to less soft rot on leaves;E. coliO157:H7 had no such effects. As soft rot signals a food safety risk, the reduction of soft rot symptoms in the presence ofS. entericamay lead consumers to eat healthy-looking butS. enterica-contaminated produce.

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Fate of Salmonella enterica and Enterohemorrhagic Escherichia coli on Vegetable Seeds Contaminated by Direct Contact with Artificially Inoculated Soil during Germination

Journal of Food Protection ◽

10.4315/jfp-20-021 ◽

2020 ◽

Vol 83 (7) ◽

pp. 1218-1226

Author(s):

YUE CUI ◽

DA LIU ◽

JINRU CHEN

Keyword(s):

Escherichia Coli ◽

Direct Contact ◽

Bacterial Pathogens ◽

Enterohemorrhagic Escherichia Coli ◽

Tissue Samples ◽

Tomato Seedlings ◽

Tissue Sections ◽

Germination Process ◽

The Mean ◽

Alfalfa Sprouts

ABSTRACT Contaminated vegetable seeds have been identified as a potential source of foodborne bacterial pathogens. This study was undertaken to observe the behavior of Salmonella and enterohemorrhagic Escherichia coli (EHEC) on vegetable seeds, contaminated by direct contact with artificially inoculated soil, during germination. Sterile sandy soil inoculated with lyophilized cells of four individual strains of Salmonella or EHEC (three O157:H7 strains and one O104:H4 strain) was mixed with sanitized seeds (2 g) of alfalfa, fenugreek, lettuce, and tomato at 20°C for 1 h. The contaminated seeds were germinated on 1% water agar at 25°C for 9 days in the dark. Populations of Salmonella and EHEC on various tissues (seed coat, root, cotyledon, and stem, etc.) of sprouts and seedlings were determined every other day over the germination period. Overall, 70.4 and 72.4% of collected tissue samples (n = 544) tested positive for Salmonella and EHEC, respectively. In general, the mean populations of Salmonella and EHEC on sprout and seedling tissues increased with the prolongation of germination time. Seed coats had the highest bacterial counts (4.00 to 4.06 log CFU/0.01 g), followed by the root (3.36 to 3.38 log CFU/0.01 g), cotyledon (3.13 to 3.38 log CFU/0.01 g), and stem tissues (2.67 to 2.84 log CFU/0.01 g). On average, tissue sections of fenugreek sprouts and lettuce seedlings had significantly higher (P < 0.05) numbers of Salmonella and EHEC cells than that of alfalfa sprouts and tomato seedlings. Data suggest that the growth and dissemination of Salmonella and EHEC cells on alfalfa, fenugreek, lettuce, and tomato sprout and seedling tissues are influenced by the type of vegetable seeds and sprout and seedling tissues involved. The study provides useful information on the fate of two important foodborne bacterial pathogens on selected vegetable seeds, contaminated by direct contact with inoculated soil, during the germination process. HIGHLIGHTS

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