3 Detection of Human Pathogens on Plants

Transcript

Hello!! Welcome to the third talk of the week that is Detection of Human Pathogens on Plants. We have seen that recently lot of human diseases are causing because of the contaminated raw foods that people consume and certain human pathogens that are being associated with this leafy root vegetables particularly, and because of consumption of such human pathogen associated plant product is casing certain ailments in human and that is why diagnosis of such human pathogens on plants is highly essential. What is the significance human pathogen? We always know that unlike most plant pathogens human pathogens that associate with plants often fail to multiply in plant host and usually occur in low numbers. But, nevertheless, they are able to cause disease in human beings despite their low population in the plant host. National and International disease outbreaks associated in human pathogens on plant products, such as lettuce, peanuts, green onions, seeds. sprouts, peppers, spices, tomatoes and cantaloupes, have occurred frequently. Current standardized assays for the detection of major pathogens on plants rely largely on microbiological, biochemical, and immunological analyses that are laborious and time consuming.

So, newer molecular- based methods, such as PCR, loop mediated isothermal amplification or (LAMP), and metagenomics approaches offer enhanced speed and sensitivity, and some of these have already incorporated into the standard assays. So these are the tools that are used for the detection of human pathogens in plants. Certain human pathogens, especially enteric microbes such as pathogenic Escherichia coli and Salmonella species., also contaminate, colonize and even invade plants. Human diseases caused by such plant contaminants are becoming more common, widespread, and consequential, and national food safety agencies across the globe are seeking greater understanding of the mechanisms and interactions of human pathogens on plants (HPOPs). Increasing opportunities for interactions, collaborations and cooperation among plant pathologists and food microbiologists, a cross-disciplinary synergy has developed from which novel, robust and sustainable solutions to human pathogen on plants (HPOP) challenges have emerged. Fresh produce has been associated repeatedly, and with increasing frequency, with outbreaks of food borne illnesses. Particularly, green leafy vegetable, melons, sprouts, berries, tomatoes and green onions, often eaten with little or no processing steps to eliminate pathogens, are among the most common produce implicated. Shiga toxin-producing Escherichia coli O157: H7 has been found on leafy greens, then Salmonella spp. on tomatoes, peppers and cantaloupes, hepatitis A virus on green onions, Shiga toxin-producing E. coli strain O104 on fenugreek seeds, sprouts and Listeria monocytogenes on cantaloupe. These are some of the reported human pathogens strains that are found associated with such green leafy vegetables.

In many cases contamination occurs either in the field or in the processing phase. Many human pathogen on plants (HPOPs) exist in environments where plants are grown and that can be the danger of the particular phenomenon of human pathogens can be analyse through that in a single year that is (2011–2012) the Food and Drought Administration (FDA) in USA issued recalls of 56 produce items including fresh-cut fruit and vegetables and bagged vegetables that contained Listeria spp., pathogenic E. coli or Salmonella. So this is not a small problem so this is becoming a huge problem as many of the human pathogens they are present in the environments where plants are grown or may be at the time of processing these contamination takes place.

So, opportunities for human pathogen on plants (HPOP) contamination of fresh produce begin on the farm and continue through all nodes of the food production and distribution chain, not ending till the food is consumed. So that is why so it originates in the field and it comes to the plate of the human who is consuming the food. So the chain continues till the last moment till the patient or the human is suffered from such pathogenic strains of microbes. How pathogens move, directly or indirectly, from vertebrate sources into plant foods can be a complex and multi-faceted phenomenon. Therefore, understanding these sources and pathways is critical for the development of prevention and mitigation strategies. Interestingly, the Gram negative bacterial family Enterobacteriaceae, which includes many of the human pathogens associated with plant foods (e.g., Escherichia, Salmonella, Shigella), also contains several plant pathogens (Enterobacter, Erwinia, Pantoea, Pectobacterium, etc.). So, it is very interesting that how this bacteria compete with each other because these human pathogens has to come in a competition with the plant pathogens.

The taxonomic relatedness of these plant and human pathogens raises interesting questions about the possibilities of niche competition or synergism, horizontal gene exchange in protected plant niches, or even host range expansion. So, co-existence of the human pathogen along with plant pathogen has the additional trick of horizontal gene transfer. Suppse, for example toxin producing gene from Escherichia coli, Salmonella if it is horizontally transferred to a plant pathogen like Erwinia and Pantoea. Then the plant pathogen can also release certain toxins to the plants it is infecting and thereby causing more damage to the consumer.

A few cross-kingdom pathogens such as Pseudomonas aeruginosa, Burkholderia cepacia, Dickeya spp., Enterococcus faecalis and Serratia marcescens actually cause disease on both plants and humans. So this is another concern that some of the microbes that causes human diseases are also able to cause plant diseases. So, this is again a grave concern for all of us.

Challenges

What are the challenges because identification of human pathogens on plants is highly essential but their identification is not a easy task, so there are certain challenges. So one of those if High Background Microflora, that is – Low Numbers of Target Human Pathogens. So in a plant community as we have mentioned earlier the population of the human pathogen is normally low because the environment is not exactly suitable for their multiplication unlike the plant associated microbes. So, in a high background of different Microflora identification or detection of human pathogen has remained to be a challenge.

Perishable Nature of Plant is another problem. Some of the plant samples they get perished very quickly. So detecting human pathogens in those plants samples is therefore very very difficult.

Nonhomogeneous Distribution of Target Pathogens in Plant Samples – So that is another issue where the entire plant sample lot may not carry the human pathogen but may be a part of plant sample is carrying the human pathogen but still it causes enough danger to the consumers. Moving Target – Then it’s always on move and that is why it’s always a difficult task. Then, Detection and Predicting Infectivity is not also very easy. So, these are certain challenges for which it is difficult to identify and detect human pathogens on plants.

Detection of Human Pathogens on Plants – detection of human pathogens and plants are basically done through – Standard Assays like Culture-Based methods. The microbes that can be cultures easily, can be easily identified. Then Molecular methods are also used for detection of human pathogens on plants such as PCR-Based methods, DNA Microarrays and Next[1]Generation Sequencing (NGS). Further, Biosensor-Based Techniques are also being deployed for detection of human pathogens on plants.

Microbes withdrawn from agricultural use – So, there are certain interesting phenomenon that was already prevailed and this has to be now modified or changed for example :- Pseudomonas aeruginosa is a case which is basically a Gram-negative environmental species and it is also an opportunistic microorganism. So, it establishes itself in vulnerable patients, such as those with cystic fibrosis or hospitalized in intensive care units (ICU). It has been a major cause for nosocomial infections worldwide and a serious threat to Public Health. But the same Pseudomonas aeruginosa is a very good plant good promoter and it has been used widely some years ago in agricultural crop production. So, there was every possibility that this particular microbe Pseudomonas aeruginosa will enter into the food chain and can cause disease to those people who are suffering from cystic fibrosis or if someone is admitted in the ICU. So realizing the threat of this kind of microorganism regulatory measures has been adopted and these microbes are now not recommended for use in agricultural crop production. But this is just a few examples but we have to screen other microbes also for being a potential human pathogen and only after that we can stop using those or we can deploy more sensitive methods for detection of such pathogens on the food that we consume and that is why it is important to take appropriate measures so that we can have supply of healthy and nutritious food to the consumers. So with this we have to an end of today’s talk that is Detection of Human Pathogens of Plants and we have seen the significance, what is the necessity of this kind of technology, why it is important to diagnose human pathogens on plants as we have seen that certain strains of pathogen is causing severe illness to the consumers.

So with this we come to an end and in the next talk we will be talking about Plant and microbial forensics and till then have a good time.

Thank you very much.