Extracts from genetically engineered plants could fight food-borne E. coli

Engineering plants to produce antibacterial proteins could offer a new way to control disease-causing E. coli in fresh food, according to a study in PNAS. Researchers genetically engineered plants to produce colicins – proteins which kill or inhibit the growth of E. coli – and found that when extracted, the colicins significantly reduced bacterial populations in meat spiked with a dangerous strain of E. coli. The authors note there are around 100, 000 E. coli-related illnesses a year in the US, many of which are linked to animal products and more recently organic vegetables, and that plant-produced colicins could be an effective food treatment.

 

Dr. Tsafrir Mor, Professor, The Biodesign Institute and the School of Life Sciences, Arizona State University (webpage):

Expertise: Molecular biology, biochemistry. Using plants to produce useful and therapeutic polypeptides, proteins and enzymes.

“The paper by the research groups from Nomad Bioscience and Icon Genetics brings another beautiful example of the power of plant-based system to produce huge quantities of proteins that can find utility in human and veterinary medicine, agriculture, the food industry and as the case presented here, in all three.

“Using Nomad/Icon’s constantly improving and evolving plant-virus based expression systems (systems that use the genetic machinery of two compatible plant viruses, tobacco mosaic virus and potato-virus X), their scientists demonstrate fantastically high levels of expression of a group of diverse bacterial proteins with strong and broad bactericidal activities in several plant species: tobacco, beet, and spinach. The recombinant proteins, colicins in this case, accumulate over about a week, when leaves are harvested and the proteins are purified.

“Colicins are naturally produced by various strains of Escherichia coli to limit the growth of competing bacterial communities. The strong anti-bacterial activities of colicins prompted the idea to use them in-lieu of traditional small molecule antibiotics, either in humans or animals, or to treat food products, like raw meat. It is this latter potential use that is explored in the Schulz et al paper.  The authors demonstrate the bactericidal activities of plant-produced colicins against the seven most common human pathogenic E. coli strains (“Big 7”). These food-borne pathogens are all too commonly found to adulterate meat products as well as fruits and vegetables, primarily organically produced.

“The article is straightforward in its approach, immaculate in its execution and convincing in its conclusion. The next move would be transfer of this technology to another company that would take plant-produced colicins through the regulatory approval process and bring them to the market.”

 

Dr. Francisco Diez-Gonzalez, Professor of Food Safety Microbiology, University of Minnesota (webpage):

Expertise: Pre-harvest ecology of foodborne pathogens; Safety of organic foods; Safety of dairy foods.

“The recent report by Schulz et al presents a unique approach to specifically control Escherichia coli in beef carcasses. It proposes the mass production of an antimicrobial set of substances, that have been known about for almost a century, using transgenic tobacco plants. In the early days of microbiology, colicins were extensively characterized and the E. coli strains that produced them were even marketed to treat some conditions such as infantile diarrhea.

“The emergence of enterohemorrhagic E. coli as serious foodborne pathogens prompted renewed interest in these type of bacteriocins. Within the last 20 years, several studies have used either colicinogenic strains or colicin-containing culture extracts with promising and sometimes limited results.

“This relevance of this report stems from several factors:

  1. using multiple colicins to anticipate the possible natural resistance of some strains to individual colicins;
  2. employing an ingenious biotechnology approach to mass produce colicins in tobacco plants; and
  3. preliminary data that the combination of two of those colicins obtained from plants could reduce the count of a single E. coli strain in meat samples.

“These findings are intriguing enough to warrant further investigation, but it is premature to claim that it could be a feasible and effective approach. Before this alternative solution can be seriously considered for commercialization, extensive studies demonstrating the wide-spectrum activity of this combination of colicins against a larger collection of E. coli strains should be conducted. In addition, the economic feasibility studies should include comparisons against other type of interventions that the meat industry has been using with relatively good success for sometime. 

“Despite the claim that colicins could be considered ‘natural’, the organic standards would not allow this kind of ingredient in organically labeled foods because they would be considered genetically modified. It is also important to clarify that despite the claim in the paper’s abstract that only thermal processing effectively controls bacteria, it is good to remember that there are at least a couple of non-thermal technologies that are quite effective: high pressure processing (HPP) and irradiation.”

 

Declared interests (see GENeS register of interests policy):

No interests declared

 

Reference

Broad and efficient control of major foodborne pathogenic strains of Escherichia coli by mixtures of plant-produced colicins‘ by Steve Schulz et al., published in PNAS on Monday 7 September, 2015. 

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