Research articles

By Ms. Vaishnavi M Ansingkar , Dr. Nikhilesh S Kulkarni
Corresponding Author Ms. Vaishnavi M Ansingkar
Microbiology Research Lab R. A. College , Civil lines Washim - India
Submitting Author Ms. Vaishnavi M Ansingkar
Other Authors Dr. Nikhilesh S Kulkarni
R.A.College, Washim, Microbiology research Laboratory - India 444505


Salmonella typhimurium, Xanthomonas campestris, Spinach, Tomato, Cucumber, Cabbage, Cauliflower

Ansingkar VM, Kulkarni NS. Studies on Survival of Salmonella Typhimurium in Phytopathogen Damaged and Healthy Fresh Produce. WebmedCentral MICROBIOLOGY 2013;4(2):WMC003988
doi: 10.9754/journal.wmc.2013.003988

This is an open-access article distributed under the terms of the Creative Commons Attribution License(CC-BY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Submitted on: 02 Feb 2013 12:12:45 AM GMT
Published on: 02 Feb 2013 07:10:44 AM GMT


The ecology of vegetable surface is important to the survival of enteric pathogens. Understanding changes in ecological parameters during the preharvest stages of production can lead to the development of approaches to minimize the hazard of contamination of vegetables with foodborne pathogens. In the present study, survival of Salmonella typhimurium at the time of harvest were compared among the phytopathogen damaged and healthy vegetables. The population density of Salmonella typhimurium decreased over time in the fresh produce regardless the treatment. The salmonella typhimurium count was found to be higher in phytopathogen damaged produce than the healthy produce. The present investigation revealed that, maintaining healthy plants and minimizing biological damage around the time of harvest might improve the safety of fresh produce.

Key wordsSalmonella typhimurium, Xanthomonas campestris, spinach, tomato, cucumber, cabbage, Cauliflower.


Epidemiology of food borne diseases is rapidly changing (1). Raw produce is regularly identified as a source of human gastrointestinal tract infection. Although the phyllosphere of plant is harsh environment for enteric human pathogens to survive, leafy green vegetables have been implicated as a source in several food borne infections (1). Phyllosphere location is subject to rapid and large fluctuation in temperature, humidity and osmotic pressure that resist bacterial proliferation on fresh produce (2). In addition, competition for limited water and nutrients makes it difficult for transient microorganisms to survive on leaf surface (3). However, damage of leafy vegetables may alter the phyllosphere microenvironment aiding in both the attachment and survival of enteric pathogens, such as Salmonella typhimurium. Infection of plants and subsequent lesion formation can also alter the microenvironment of leaf surface and favors the attachment and survival of foodborne pathogens (4). Despite of these advances in knowledge, there is scarcity of information regarding the extent to which phytopathogenic bacteria enhance the survivability of enteropathogens on fresh produce. Hence, the present investigation was carried out, with an objective to determine the extent to which phytopathogenically damaged fresh produce supports the survival of Salmonella typhimurium in edible portion of the plant and their comparative evaluation among healthy plants.

Materials And Methods

The fresh produce namely spinach, tomato, cucumber, cabbage and cauliflower were selected as a test plants for present study. The phytopathogen Xanthomonas campestris was isolated from respective diseased plants and used for induction of plant infection. The plants without Xanthomonas campestris infection were maintained as control. Treatments were applied after the plants were 7 weeks old. The test plants were spray inoculated with Xanthomonas campestris (app.108 CFU/mL) until runoff. The misting was carried out with deionised water for 36 sec, 2 times per hour (4). Misting was discontinues once the necrotic lesions were observed. The test and control plants were swabbed with cotton applicator that was dipped in Xanthomonas campestris broth having density app. 107 CFU/mL. A new applicator was used for each plant (4).

The edible portion of the all fresh produces was collected at the time of harvest i.e. on 57, 58, 59 and 60 days after sowing (DAS). All the samples were collected in sterilized polybags and transported to laboratory and stored at 40C until processing. Tissue homogenate of all the surface sterilized samples were obtained and enriched in tryptone broth @10% at 370C for 24 hours. The enriched samples were serially diluted and used for the enumeration of Salmonella typhimurium adopting standard plate count method on Bismuth sulphite agar.

Results and Discussion

The Salmonella typhimurium was inoculated to each fresh produce in similar manner and the initial count were found to be higher in all the test crops and over the time the population density was also decreased.

In case of Xanthomonas campestris infected tomato and spinach the maximum number of Salmonella typhimurium was found as log 5.5390 and 5.4800 respectively at 57 DAS, while lowest count was log 4.8147 and 4.1903respectively at 60 DAS. These results are in accoerance with Aruscavage et al (4). Similar trend of population densityof Salmonella typhimurium was also observed in cucumber, cabbage and cauliflower.

In all the test fresh produce, population density of Salmonella typhimurium was ranged between log 5.5309 to 1.2304 in Xanthomonas campestris infected samples. While in control it was log 4.4183 to 1.0043. This indicates that, the higher density of Salmonella typhimurium was exists in phytopathogen damaged plants as compared to healthy plants.

Similarly in other study, mechanically damaged wounds of apples supported 1to 3 log increase in growth of Escherichia coli O157:H7 compared to nondamaged apple tissues(5). Likewise, Seo and Frank, (6) demonstrated that Escherichia coli O157:H7 was more likely  to attached at cut sites on lettuce leaves than at intact sites. Additionally, Salmonella spp. and Shigella sonnei grew more rapidly and to larger population size on chopped leaves of cilantro and parsley respectively than on whole leaves.

The damaged leaves released more nutrients onto the leaf surface. However, these nutrients are not homogeneously distributed to the leaf surface, and thus, motility of microorganisms is important for survival (7). The enteric pathogens considered in the present investigation is either motile, which enables it to survive on the fresh produce surface.

The present investigation revealed that, Salmonella typhimurium population declined quickly and greatly in case of control but, the survival was enhanced in Xanthomonas campestris infected plants. This is probably because of the availability of nutrients on fresh produce, which become available as a result of lesion formation due to phytopathogen damaged.

Jablasone et al., (8), demonstrated the Escherichia coli O157:H7 population decrease on the surface of alfalfa seedlings, because as the plant becomes mature, nutrient availability decreased on healthy plant. However, the larger amount of nutrients expelled on damaged leaves might contribute to the observed increased in survival of enteric human pathogens.

In contrast with the present study, infection of biotrophic phytopathogen Glomerulla cingulata did not increase the number of enteropathogens. (3), however, that study was related to apple contamination. In other study, the role of mechanical and biological damage in the survival of Escherichia coli O157:H7 showed increase in proliferation on apples (5).

The damaged tissue or lesions could provide protection from the environmental stress. Escherichia coli O157:H7 attaches preferentially to cut or injured surface and could penetrate into the cuts, protecting the pathogens from the environment (6). Our results are in accordance with this study. Once the pathogen gets located in internalized tissues of fresh produce, they get protected from the biocidal washing treatment after harvest, which ultimately reduces the efficacy of postharvest washing treatment.

Overall, the studies described herein, revealed that phytopathogen damage of fresh produce can greatly enhance its colonization with enteric human pathogens viz., Escherichia coli O157:H7 and Salmonella spp.  Hence, in order to reduce disease outbreaks associated with fresh produce, it is important to protect the fresh produce from attack of phytopathogen; this might be helpful to improve food safety.


1. Tauxe, R.V. 1997: Emerging foodborne diseases: an evolving public health challenges. Emerg. Infect. Dis. 3:425-434
2. Wilson, M. S., S. Hirano, and S. E. Lindow. 1999:  Location and survival of leaf associated bacteria in relation to pathogenicity and potential for growth within the leaf. Appl. Environ. Microbiol.65:1435-1443.
3. Riordan, D.C.R.,G.M.Sapers and B.A.Annous. 2000: The survival of Escherichia coli O157:H7 in presence of Penicillium expansum and Glomerula cingulata in wounds on apple surfaces. J.Food Prot. 63:1637-1642
4. Aruscavage D.,S.A.Miller,M.L.Lewisivey, K.Lee and J.F.LeJeune 2008: Survival and dissemination of Escherichia coli O157:H7 on physically and biologically damaged lettuce plants.J. Foof Prot. 71(12):2384-2388.
5. Janisiewski, W.J.,W.S.Conway, M. W. Brown, G.M.Sapers, P. Fratamico and L.R.Buchanan 1999: Fate of Escherichia coli O157:H7 on fresh –cut apple tissues and its potential for transmission by fruit flies Appl. Environ. Microbiol. 65:1-5.
6. Seo K.H. and J.F. Frank 1999: Attachment of Escherichia coli O157:H7to lettuce leaf surface and bacterial viability in response to chlorine treatment as demonstrated by using confocal scanning laser microscopy. J. Food Prot. 62:3-9
7. Liao, C. and W.F.Fett 2001: Analysis of native microflora and selection of strains antagonistic to human pathogens on fresh produce J. Food Prot64:1110-1115.
8. Jablasone, J., K.Warriner and M.Griffiths 2005: Interactions of Escherichia coli O157:H7, Salmonella typhimurium and Listeria monocytigens in a genobiotic system. Int.J.Food Microbiol. 99:7-18.

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