Tag Archives: internalization

Internalization and fate of Escherichia coli O157:H7 in leafy green phyllosphere tissue using various spray conditions

Posted on by
Reply

In the past decade, leafy greens have been implicated in several outbreaks of foodborne illness, and research has focused on contamination during preharvest operations. Concerns have been raised that internalization of pathogens into the edible tissue occurs where postharvest chemical interventions would be ineffective. This study was initiated to measure the lettucedegree and fate of Escherichia coli O157:H7 internalized in the phyllosphere tissue of leafy greens when spray conditions, inoculum level, and type of leafy green were varied. Two spraying treatments were applied: (i) spraying individual spinach or lettuce leaves on plants once with a high dose (7 to 8 log CFU/ml) of E. coli O157:H7 and (ii) spraying spinach, lettuce, or parsley plants repeatedly (once per minute) with a low dose (2.7 to 4.2 log CFU/ml) of E. coli O157:H7 over a 10- to 20-min period. With the high-dose spray protocol, no significant differences in the prevalence of internalization occurred between Shiga toxin–negative E. coli O157:H7 isolates and virulent isolates (P > 0.05), implying that the Shiga toxin virulence factors did not influence internalization or the subsequent fate of those populations under these test conditions. Significantly greater internalization of E. coli O157:H7 occurred in spinach leaves compared with lettuce leaves when leaves were sprayed once with the high-dose inoculum (P < 0.05), whereas internalization was not observed in lettuce leaves but continued to be observed in spinach and parsley leaves following repeated spraying of the low-dose inoculum. Based on these results, it is surmised that a moisture film was generated when spraying was repeated and this film assisted in the mobilization of pathogen cells to plant apertures, such as stomata. E. coli O157:H7 cells that were internalized into spinach tissue using a low-dose repeat-spray protocol were temporary residents because they were not detected 2 days later, suggesting that plant-microbe interactions may be responsible.

Journal of Food Protection®, Number 5, May 2014, pp. 696-863 , pp. 713-721(9)

Erickson, Marilyn C.1; Webb, Cathy C.2; Davey, Lindsey E.2; Payton, Alison S.2; Flitcroft, Ian D.3; Doyle, Michael P.2

Effects of post-harvest handling conditions on internalization and growth of Salmonella Enterica in tomatoes

Posted on by
Reply

Journal of Food Protection®, Number 3, March 2014, pp. 352-521 , pp. 365-370(6)

Zhou, Bin; Luo, Yaguang; Nou, Xiangwu; Yang, Yang; Wu, Yunpeng; Wang, Qin

http://www.ingentaconnect.com/content/iafp/jfp/2014/00000077/00000003/art00003

Salmonella internalization in tomatoes during postharvest handling is a major food safety concern. This study was conducted to determine the effect of immersion time, immersion depth, and temperature differential between bacterial suspension and tomato pulp on the internalization of Salmonella enterica in tomato fruits. The effect of storage temperature and tomato.dump.tankduration on the survival and growth of internalized Salmonella cells was also evaluated. Overall, immersion time significantly affected the incidence and extent of S. enterica internalization (P < 0.0001), with a linear correlation between immersion time and Salmonella internalization. The depth of Salmonella internalization in tomato tissues also increased with increasing immersion time. Immersion time also significantly influenced the degree to which the temperature differential affected Salmonella internalization. With an immersion time of 2 min, the temperature differential had no significant effect on Salmonella internalization (P = 0.2536). However, with an immersion time of 15 min, a significantly larger Salmonella population became internalized in tomatoes immersed in solutions with a –30°F (–16.7°C) temperature differential. Internalized S. enterica cells persisted in the core tissues during 14 days of storage. Strain type and storage duration significantly affected (P < 0.05) both the frequency detected and the population of internalized Salmonella recovered, but storage temperatures of 55 to 70°F (12.8 to 21.1°C) did not (P > 0.05). These findings indicate the importance of preventing pathogen internalization during postharvest handling.

 

Pathogen internalization by root uptake into food crops

Posted on by
Reply

Can pathogens like E. coli or Salmonella be internalized by growing fresh produce like lettuce, spinach and tomatoes?

Depends.

Researchers from the University of Delaware and the U.S. Department of Agriculture report in Foodborne Pathogens and Disease that enteric pathogens localized at subsurface sites on leafy green plant tissue prevent their removal during washing and inactivation by sanitizers. Root uptake of enteric pathogens and subsequent internalization has been a large area of research with results varying due to differences in experimental design, systems tested, and pathogens and crops used.

The potential for uptake of foodborne pathogen, both bacterial and viral, through roots into food crops is reviewed. Various factors shown to affect the ability of human pathogens to internalize include growth substrate (soil vs. hydroponic solution), plant developmental stage, pathogen genus and/or strain, inoculum level, and plant species and cultivar. Several mechanisms of internalization (“active” vs. “passive”) of bacteria to plant roots have also been hypothesized.

The authors do conclude:

• uptake through internalization is a plant–pathogen specific interaction;
• the plant growth substrate used plays a large role in the uptake of both
bacterial and viral pathogens in plants;
• intact, healthy, non-injured roots seem to discourage the uptake of bacteria cells and viruses into plants; and,
• generally, the presence of internalized pathogens in roots of plants does not directly correlate with internalized pathogens in the edible or foliar tissues of crops.

The authors also note that contaminated soil, for the most part, resulted in little to no observed internalization as compared to contaminated hydroponic solution.

Pathogen internalization by root uptake into food crops

Posted on by
Reply

Can pathogens like E. coli or Salmonella be internalized by growing fresh produce like lettuce, spinach and tomatoes?

Depends.

Researchers from the University of Delaware and the U.S. Department of Agriculture report in Foodborne Pathogens and Disease that enteric pathogens localized at subsurface sites on leafy green plant tissue prevent their removal during washing and inactivation by sanitizers. Root uptake of enteric pathogens and subsequent internalization has been a large area of research with results varying due to differences in experimental design, systems tested, and pathogens and crops used.

The potential for uptake of foodborne pathogen, both bacterial and viral, through roots into food crops is reviewed. Various factors shown to affect the ability of human pathogens to internalize include growth substrate (soil vs. hydroponic solution), plant developmental stage, pathogen genus and/or strain, inoculum level, and plant species and cultivar. Several mechanisms of internalization (“active” vs. “passive”) of bacteria to plant roots have also been hypothesized.

The authors do conclude:

• uptake through internalization is a plant–pathogen specific interaction;
• the plant growth substrate used plays a large role in the uptake of both
bacterial and viral pathogens in plants;
• intact, healthy, non-injured roots seem to discourage the uptake of bacteria cells and viruses into plants; and,
• generally, the presence of internalized pathogens in roots of plants does not directly correlate with internalized pathogens in the edible or foliar tissues of crops.

The authors also note that contaminated soil, for the most part, resulted in little to no observed internalization as compared to contaminated hydroponic solution.

Can E. coli get inside plant vascular system? 2009 research says unlikely

Posted on by
Reply

The paper was published in July 2009 but the U.S. Department of Agriculture put out a press release today saying that Escherichia coli is not likely to contaminate the internal vascular structure of field-grown leafy greens and thus increase the incidence of foodborne illness.

The timing was probably coupled with pretty pictures of the research, appearing in the April 2011 issue of USDA’s Agricultural Research magazine.

Agricultural Research Service (ARS) microbiologist Manan Sharma wanted to find out if plant roots could draw in E. coli pathogens from the soil when taking in nutrients and water. He and colleagues modified several types of E. coli—including some highly pathogenic strains that cause foodborne illness—by adding a gene for fluorescence. This allowed them to track the pathogen’s journey from the field to the produce.

The team, which is located at the ARS Environmental Microbial and Food Safety Laboratory in Beltsville, Md., confirmed that the pathogenic E. coli could survive in the soil for up to 28 days. They also observed that the fluorescent E. coli cells were capable of migrating into the roots of spinach plants.

The researchers also examined baby spinach plants over the course of 28 days after germination to see if any of the E. coli strains were taken up past the roots and into the plant’s interior structures. For this part of the study, they grew baby spinach in pasteurized soil and hydroponic media.

At day 28, there was no evidence that the E. coli had become "internalized" in leaves or shoots of baby spinach plants grown in the pasteurized soil. E. coli could be detected in hydroponically-grown spinach samples, but its survival in shoot tissue was sporadic 28 days after the plants had germinated.

These findings strongly suggest that although E. coli can survive in soils, it’s highly unlikely that foodborne illness would result from the bacterium becoming "internalized" through roots in leafy produce.

Chapman reviewed the idea of internalization of human pathogens by plants for barfblog in 2008 and it’s available at
http://barfblog.foodsafety.ksu.edu/blog/139669/08/05/28/pathogens-produce-brief-review

The original abstract is below:
A novel approach to investigate the uptake and internalization of Escherichia coli O157:H7 in spinach cultivated in soil and hydroponic medium.
Sharma M, Ingram DT, Patel JR, Millner PD, Wang X, Hull AE, Donnenberg MS.
J Food Prot. 2009 Jul;72(7):1513-20.

Internalization of Escherichia coli O157:H7 into spinach plants through root uptake is a potential route of contamination. A Tn7-based plasmid vector was used to insert a green fluorescent protein gene into the attTn7 site in the E. coli chromosome. Three green fluorescent protein-labeled E. coli inocula were used: produce outbreak O157:H7 strains RM4407 and RM5279 (inoculum 1), ground beef outbreak O157:H7 strain 86-24h11 (inoculum 2), and commensal strain HS (inoculum 3). These strains were cultivated in fecal slurries and applied at ca. 10(3) or 10(7) CFU/g to pasteurized soils in which baby spinach seedlings were planted. No E. coli was recovered by spiral plating from surface-sanitized internal tissues of spinach plants on days 0, 7, 14, 21, and 28. Inoculum 1 survived at significantly higher populations (P < 0.05) in the soil than did inoculum 3 after 14, 21, and 28 days, indicating that produce outbreak strains of E. coli O157:H7 may be less physiologically stressed in soils than are nonpathogenic E. coli isolates. Inoculum 2 applied at ca. 10(7) CFU/ml to hydroponic medium was consistently recovered by spiral plating from the shoot tissues of spinach plants after 14 days (3.73 log CFU per shoot) and 21 days (4.35 log CFU per shoot). Fluorescent E. coli cells were microscopically observed in root tissues in 23 (21%) of 108 spinach plants grown in inoculated soils. No internalized E. coli was microscopically observed in shoot tissue of plants grown in inoculated soil. These studies do not provide evidence for efficient uptake of E. coli O157:H7 from soil to internal plant tissue.