Bacterial and plant factors that influence adhesion of enterohaemorrhagic E. coli and Salmonella enterica to salad leaves
Lead Research Organisation:
Harper Adams University
Department Name: Agriculture and Environment
Abstract
Until now, research into transmission of food-borne pathogens has largely focused on farm animal reservoirs. Although transmission of enteric pathogens via salad leaves is on the rise, only a few studies have addressed the molecular mechanisms used by human enteric bacterial pathogens to attach to plants. Likewise there have been few studies investigating variation between plant genotypes on bacterial adhesion and/or survival and those that have not addressed the genetic basis of any differences. In this project we aim to investigate how human bacterial pathogens attach to salad leaves (in particular lettuce). We will determine the effect of bacterial growth condition on the ability of the organism to attach to leaves. Similarly, we will determine the effect of plant growth conditions on susceptibility to bacterial attachment. Using genetic approaches, we will determine which bacterial genes are involved in leaf attachment and we will utilise a lettuce mapping population of recombinant inbred lines to initiate studies aimed at gaining an understanding of the genetic basis of a plant's susceptibility to bacterial adhesion. We will also determine survival and replication rates of Salmonella and E. coli on the different lettuce lines. The ultimate goal of our studies is to provide the underpinning knowledge of the interaction between the plant and enteric bacteria in the phyllosphere to allow the development of strategies to reduce the risk of crop contamination and to increase food safety.
Technical Summary
Traditionally, research into food borne pathogens in the UK has focused on zoonosis. However, recent surveys have shown that while there is a reduction in transmission of non-typhoidal serovars of Salmonella enterica via contaminated poultry products, there is a steep rise in transmission via salad leaves, particularly, but not exclusively, lettuce. Similarly, although Infections with enterohaemorrhagic E. coli (EHEC) are usually linked to consumption of contaminated beef products, sever outbreaks in Sakai city in 1996 and the US in 2006 were traced to consumption of contaminated radish sprouts and pre-packed lettuce, respectively. Only a few studies have addressed the molecular mechanisms used by human enteric bacterial pathogens to attach to plants. Likewise there have been few studies investigating variation between plant genotypes on bacterial adhesion and survival and those that have been carried out do not address the genetic basis of any differences. In this project we will determine the mechanisms used by S. enterica & EHEC (O157 and non-O157) to attach to salad leaves. We will determine the effect of bacterial growth conditions on leaf attachment potential. We will use immunofluoresence microscopy, scanning electron microscopy and viable counts to determine the level and pattern of adhesion and to visualize potential adhesion factors. We will determine survival and replication rates in planta. Combining with site directed mutagenesis, this will reveal common and species-specific leaf adhesion and survival strategies. We will also investigate host factors that contribute to leaf susceptibility to colonisation. We will determine the effect of plant growth conditions and age on colonisation by S. enterica & EHEC. Using genetic and genomic approaches we will initiate studies to determine the genetic basis of lettuce to susceptibility to colonisation. These studies will underpin development of new risk assessments and improvements in food safety.
Organisations
People |
ORCID iD |
Paul Hand (Principal Investigator) | |
David Pink (Co-Investigator) |
Publications
Hunter PJ
(2010)
Both leaf properties and microbe-microbe interactions influence within-species variation in bacterial population diversity and structure in the lettuce (Lactuca Species) phyllosphere.
in Applied and environmental microbiology
Berger CN
(2010)
Fresh fruit and vegetables as vehicles for the transmission of human pathogens.
in Environmental microbiology
Description | There were 3 significant discoveries arising from this grant as follows: 1. The identification of plant traits which affect pathogen attachment, especially specific compounds such as phenolics which are involved in plant defence responses. 2. The significant levels of internal (endophytic) colonisation of lettuce leaves by pathogens which has implications for post-harvest processing in the salads industry. 3. The discovery of bacteria in the natural leaf microbial community which are antagonistic to human pathogens raises the possibility of natural control methods. |
Exploitation Route | Our discovery that specific physical and biochemical components of lettuce leaves affect pathogen attachment and the fact that there is a genetic component to this could be taken forward by further research to further define the underlying genetics and understand the mechanism(s) involved. The information could be used in plant breeding to develop cultivars which are less susceptible to colonisation by human pathogens. The significant degree of internal colonisation of leaves by pathogenic bacteria should be of interest to the salad processing and retail industry as it could reduce the effectiveness of current washing protocols for bagged salads. Washing and monitoring procedures should be reviewed and modified if neccessary. We discovered that some bacteria found in the leaf microbial community were able to inhibit or prevent the growth of human pathogens in vitro. Further research would be needed to confirm this and to determine the nature of the interaction, but it raises the possibility of natural control methods to reduce or prevent contamination of leaves. |
Sectors | Agriculture Food and Drink Education Healthcare Retail |
Description | DACP member of BBC Rural Affairs Connittee |
Geographic Reach | Multiple continents/international |
Policy Influence Type | Participation in a guidance/advisory committee |
Description | DACP member of Food Ethics Council |
Geographic Reach | National |
Policy Influence Type | Participation in a guidance/advisory committee |
Description | DACP parliamentary discussion on global food crisis |
Geographic Reach | National |
Policy Influence Type | Participation in a guidance/advisory committee |
Title | Bacterial 16S rRNA sequences |
Description | A total of 215 equences from 16S rRNA genes of bacteria isolated from salad leaves have been submitted to GenBank (http://www.ncbi.nlm.nih.gov/ ) and are publically available under accession numbers JQ727437 - JQ727652 |
Type Of Material | Improvements to research infrastructure |
Year Produced | 2012 |
Provided To Others? | Yes |
Impact | Improved coverage of 16S rRNA database for better understanding of bacterial population community structure in the crop environment |
URL | http://www.ncbi.nlm.nih.gov/ |
Title | Lettuce phyllosphere bacterial culture collection |
Description | A culture collection of bacteria (approx. 300 isolates) associated with epiphytic and endophytic colonisation of salad leaves was produced and is stored at Harper Adams University College. A number of these have been identified and further characterised by 16S rRNA sequence analysis, 215 sequences submitted to Genbank & publicly available |
Type Of Material | Database/Collection of data |
Year Produced | 2012 |
Provided To Others? | Yes |
Impact | Clearer understanding of the microbial community structure on (and within) leaves. |
Description | DACP BBC Countryfile interview |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Public/other audiences |
Results and Impact | not known |
Year(s) Of Engagement Activity | 2009 |
Description | DACP BBC Radio 4 interview |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Public/other audiences |
Results and Impact | invitation to attend RHS conference on Horticulture careers not known |
Year(s) Of Engagement Activity | 2012 |
Description | DACP attended RHS Conference on Horticulture Careers |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Public/other audiences |
Results and Impact | stimulated discussion of ways to encourage young people to consider careers in horticulture not known |
Year(s) Of Engagement Activity | 2012 |
Description | P Hand University Open Days |
Form Of Engagement Activity | Participation in an open day or visit at my research institution |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Schools |
Results and Impact | lively Q&A about careers in Agriculture and research Increase in student applications to Harper Adams University |
Year(s) Of Engagement Activity | 2013,2014 |
Description | P Hunter University Open Days |
Form Of Engagement Activity | Participation in an open day or visit at my research institution |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Schools |
Results and Impact | discussions with school pupils about degree choices and careers in Agriculture & land-based studies increase in student applications to Harper Adams |
Year(s) Of Engagement Activity | 2011 |